Copyright 2004 Psychonomic Society Inc 446

Perception amp Psychophysics2004 66 (3) 446-453

Change detection has been a useful tool with which tostudy visual attention and short-term memory in visualperception (Rensink 2002 for a nice collection of stud-ies see Visual Cognition 7 2000) It creates surprisingbut convincing demonstrations of how visual representa-tions are impoverished (Simons amp Levin 1997) and alsohow such representations can be enhanced by focal at-tention (Rensink ORegan amp Clark 1997) It has be-come a standard paradigm for studying properties of vi-sual short-term memory (VSTM Luck amp Vogel 1997Pashler 1988 Phillips 1974) Most studies have focusedon change detection of a collection of individual itemswith an interest in how each item is represented and howits change is detected

Change detection can also be used to probe the natureof relational encoding among items how items are per-ceptually grouped and how such grouping is carried fromperception to short-term memory One approach is to cueattention to an element within a perceptual group definedby proximity or connectedness and then test the successwith which changes of items in the same or a differentgroup are detected (Woodman Vecera amp Luck 2003)Same-group items are detected better than different-

group items are suggesting that perceptual grouping ispreserved in transferring information to short-termmemory Another approach relies on the principle of en-coding specificity (Tulving 1974) and varies the retrievalcontext so that across frames of changes the contextsurrounding the critical change either matches or mis-matches the context during encoding (Jiang Olson ampChun 2000) Using the latter approach we found that thedetection of location changes is unaffected by changes inthe color or shape of the contextual items but is disruptedby changes in the locations of the surrounding itemsThis suggests that the spatial relation formed by adjacentitems is encoded and represented in VSTM but surfacefeatures are not

In this study we further pursued the representation ofperceptual grouping in change detection tasks What roledoes perceptual grouping play in the detection of changesin item locations Our own research in the past has sug-gested that perceptual grouping plays a significant role ifit is relevant to the task but can be largely ignored if it isirrelevant to the task If for example subjects are askedto remember the locations of chromatic items and to ig-nore the locations of achromatic items then change de-tection is completely determined by changes of the chro-matic items and is unaffected by changes of the achromaticitems (Jiang et al 2000) In this case color grouping isrelevant and hence the target group (chromatic items) isattended and transferred into VSTM If however colorgrouping is irrelevant it is largely ignored For instanceconsider a set of red and green items forming two colorgroupsmdashred items and green items The perceptual orga-

We thank Mike Mangini Lawrence E Marks Robert Melara RonRensink and Rebecca Saxe for valuable comments and criticisms Thisresearch is supported in part by a Helen Hay Whitney research fellow-ship to YJ Correspondence should be sent to Y Jiang who is now atthe Department of Psychology Harvard University 33 Kirkland StreetRoom 820 Cambridge MA 02138 (e-mail yuhongwjhharvardedu)

Perceptual grouping in change detection

YUHONG JIANGMassachusetts Institute of Technology Cambridge Massachusetts

MARVIN M CHUNYale University New Haven Connecticut

and

INGRID R OLSONUniversity of Pennsylvania Philadelphia Pennsylvania

Detection of an itemrsquos changing of its location from one instance to another is typically unaffectedby changes in the shape or color of contextual items However we demonstrate here that such loca-tion change detection is severely impaired if the elongated axes of contextual items change orientationeven though individual locations remain constant and even though the orientation was irrelevant to thetask Changing the orientations of the elongated stimuli altered the perceptual organization of the dis-play which had an important influence on change detection In detecting location changes subjectswere unable to ignore changes in orientation unless additional invariant grouping cues were providedor unless the items changing orientation could be actively ignored using feature-based attention (colorcues) Our results suggest that some relational grouping cues are represented in change detection evenwhen they are task irrelevant

PERCEPTUAL GROUPING AND CHANGE DETECTION 447

nization (grouping) is preserved when these items main-tain their colors across frames but is changed if some ofthe red items swap colors with some of the green itemsNonetheless if subjects are asked to remember the loca-tions of all the items then location change detection isunaffected by such color swapping (Jiang et al 2000)Thus it appears that if color grouping is relevant to thetask then the target group is effectively selected andstored in VSTM but if it is irrelevant to the task thenchange detection of locations can proceed independentlyof changes in the perceptual organization of the display

The purpose of our present study was to demonstratethat some types of perceptual grouping cues that are ir-relevant to the task cannot be effectively ignored in changedetection We presented subjects with two dot arrays sep-arated by a brief interstimulus interval of 1 sec and thesubjects were required to remember the locations ofthese dots and to judge whether the two arrays occupiedidentical locations or whether there was a change in onelocation Using these displays we have previously shownthat change detection of dot locations was unaffected bythe color change of these items (Jiang et al 2000) Inthe present study we added a short line segment inter-posing each dot From the memory to the probe displaythese line segments either maintained their orientationor changed orientation A schematic sample of an orien-tation change is illustrated in Figure 1

Note that in this design the locations of the dots wererelevant whereas the orientations of the line segmentswere not Nonetheless elongated lines tend to group byspatial proximity The change in their orientations pro-duced a change in the proximity relations and hence in-

duced changes in perceptual grouping Can irrelevantperceptual grouping always be ignored in change detec-tion of item locations

EXPERIMENT 1

MethodSubjects Ten observers were tested in Experiment 1 The sub-

jects were recruited from Yale University Vanderbilt Universityand Harvard University Their ages ranged from 18 to 30 years Allthe subjects signed an informed consent form before the test andwere fully debriefed after the experiment They had normal orcorrected-to-normal visual acuity and normal color vision

Procedure Each trial started with a 500-msec white fixation point(03ordm 03ordm) which was followed by an initial display containingeight elements in randomly selected cells in an invisible 8 8 ma-trix that subtended 175ordm 175ordm Each item was positioned at thecenter of a cell The initial display was presented for 400 msec fol-lowed by a blank display of 1000 msec Next the probe display con-taining eight elements was presented Each element was a black dot(04ordm 04ordm) with a white line segment (12ordm 02ordm) interposed at itscenter On 50 of the trials all of the dots maintained their locationsfrom the memory to the probe display On the other 50 of the trialsone dot was randomly selected from the eight and was relocated to apreviously unoccupied cell The observers were required to press oneof two keys to report whether they detected a location change Theywere instructed that the location of an item was indicated by the blackdot and they should ignore the white line elements

In addition to location changes each line segment either main-tained its initial randomly chosen orientation or changed its orien-tation by 45ordmndash90ordm (with 50 probability) Each subject was testedin 12 practice and 80 experimental trials (80 2 location [changevs nonchange] 2 orientation [change vs nonchange] 20 cases)

Equipment The experiment was programmed using MacProbe188 (Hunt 1994) The observers were tested individually in a roomwith normal interior lighting They sat at an unrestricted distance

Time

Probe displayuntil response

Interstimulusinterval 1000 msec

Memory display400 msec

Figure 1 A schematic example of the displays used in Experiment 1 This ex-ample shows a trial in which a dot changed its location and the line segmentsall changed orientations Not shown are control trials in which the line seg-ments maintained their orientations

448 JIANG CHUN AND OLSON

from the computer screen of about 57 cm at which distance 1 cmcorresponded to 1ordm of visual angle

Data analysis In this study we calculated A as a measure of thesubjects sensitivity (Grier 1971) We also measured percent cor-rect and d The overall pattern of results were the same whether Apercent correct or d was used A was preferred as a measure ofmemory accuracy (Donaldson 1993)

ResultsMean A for change detection of dot location was 91

when the orientations of the interposing lines did notchange and was 76 when they did change This differ-ence was statistically significant [t(9) 348 p 007]Thus change detection of locations was significantly im-paired by orientation change of irrelevant line segments

DiscussionIn change detection of dot locations the subjects were

unable to ignore orientation change of interposing linesegments This suggests that at least some contextualmismatch between encoding and retrieval irrelevant tothe critical dimension of the task could not be ignored

We performed further experiments (Experiments 1Bndash1J) in order to clarify the conditions under which irrele-vant orientation changes could and could not be ignoredTable 1 summarizes the results These data ruled outsome explanations of the disruption effect observed inExperiment 1 For example (1) item rotation in generaldid not produce disruption in location change detectionas long as the item was not elongated (eg gratings andcross patterns) and (2) the amount of transient changeswas not critical because the rotation of cross patterns ledto as much (or more) transient change but did not disrupt

performance The fact that disruption was significantwhen the retention interval was only 50 msec also sug-gests that the effect is tied to the perception of the stim-uli and is not just a property of VSTM retention In sumit appears that orientation changes in the long axis ofelongated objects were critical for the disruption of lo-cation change detection

Such disruption can be accounted for by the mismatchin perceptual grouping between the memory and theprobe displays Items in an array are not represented in-dividually but relationally Orientation change in elon-gated objects altered the global organization of the itemsFigure 2 illustrates how the global organization of elon-gated items is affected by their orientations Whereas thelines on the left panel tend to be grouped horizontallyowing to spatial proximity (Palmer 1999) after a 90ordm ro-tation the lines on the right panel tend to be grouped ver-tically even though the center locations of each item didnot change

If subjects are provided with an additional explicitframe of reference that is constant across changes in ori-entation then grouping by proximity should play a smallerrole The next experiment tests this hypothesis

EXPERIMENT 2

Experiment 2 tested whether an added constant refer-ence frame would reduce the disruption effect observedin Experiment 1 This additional reference frame wasprovided in two ways Line stimuli were presented withina regularly spaced visible grid (Experiment 2A) or thecenters of line stimuli were connected by chromatic links

Table 1Location Change Detection (A) Using Various Stimuli

Type of Item Change From A With A WithoutExperiment Stimuli Memory to Probe Displays Change Change N p Level

1B Rotation 73 87 7 006ISI 1000 msec

1C Rotation 83 98 7 002ISI 50 msec

1D Addition or deletion 81 88 8 005of line segments

1E Length change 88 95 6 007Same subjects Rotation 73 94 001

1F Rotation 88 88 11 50

1G Rotation 86 88 10 35

1H Color change 88 89 7 50

1I Shape change 91 90 7 50

1J Size change 81 84 7 25

NotemdashRanges of A from 5 to 10where 5 corresponds to chance performance and 10 correspondsto perfect performance With comparable amount of end point changes rotation produced a largerdisruption effect than length change did

PERCEPTUAL GROUPING AND CHANGE DETECTION 449

(Experiment 2B) Rotations of line stimuli orientationdid not affect the location of each item within the gridand the rotations did not change the shape of the chro-matic links Thus the regular grid or the links providedconstant information that was unaffected by line orien-tation change

The constancy provided by the reference frames mighthelp subjects ignore orientation changes However it isnot obvious whether such constant invariant cues aresufficient to reduce or remove the disruption effect Infact Experiment 1 showed that the presence of invariantinformation was not always sufficient When dots werepresented at the center of each line rotating the line seg-ments did not change the position of these salient dots(see Figure 1) yet the subjects could not ignore the ori-entation change In fact the invariant central dots failedto reduce the disruption Moreover unpublished datafrom our lab have revealed the same amount of disrup-tion whether the line centers were marked or not It istherefore of interest to find out whether other types ofcues such as the presence of a regular grid might pro-vide a constant reference frame that can reduce or elim-inate the disruption effect

MethodExperiment 2A Sixteen observers were tested Each observer

performed 12 practice and 256 experimental trials Two types ofstimuli were tested line arrays without an external background gridand line arrays appearing within a regularly spaced grid As in Ex-periment 1 we varied line orientation constancy from memory toprobe displays and also varied the presence or absence of one loca-tion change Ten observers were tested in a blocked design in whichthe presence or absence of the grid were tested in separate blocksand six were tested in a mixed design The results were pooledacross these two groups because the pattern of performance wasunaffected by this design Each display contained 12 items in het-erogeneous orientations

Experiment 2B Eight observers performed 12 practice and 256experimental trials The design of this experiment was identical tothat of Experiment 2A except that we replaced the regularly spacedgrid with a connect-the-dot chromatic grid that linked the centersof all the lines The two types of displays (lines with or withoutchromatic links) were tested in separate blocks The order of theblocks (ABBA or BAAB) was counterbalanced across observersEach display contained eight items in homogeneous orientations

ResultsFigure 3 plots A of location change detection as a

function of item rotation and grouping cues For Exper-iment 2A a repeated measures analysis of variance(ANOVA) showed a significant main effect of line ori-entation change [F(115) 1211 p 003] and a sig-nificant interaction between orientation change and thepresence or absence of background grid [F(115) 720p 017] The main effect of background grid was not sig-nificant [F(115) 166 p 20] Specifically orienta-tion change produced a significant disruption on changedetection when the lines were presented without the back-ground grid [t (15) 445 p 001] In contrast orien-tation change had no effect on performance when thelines were presented on a regularly spaced backgroundgrid [t (15) 139 p 15] Thus the presence of abackground grid eliminated the disruption effect pro-duced by line orientation change

Figure 2 Change in the orientation of the long axis of an itemleads to a change in perceptual grouping

Figure 3 The results from Experiment 2 Error bars indicate standard error ofbetween-subjects variation

450 JIANG CHUN AND OLSON

For Experiment 2B an ANOVA revealed a significantmain effect of line orientation change [F(17) 3520p 001] a significant main effect of the presence orabsence of chromatic links [F(17) 3060 p 001]and a significant interaction between orientation changeand chromatic links [F(17) 1649 p 005] Pairwiset tests showed that orientation change was disruptiveboth when the chromatic links were absent (p 001)and when they were present (p 002) However thesignificant interaction indicated that the presence of aconstant chromatic link attenuated the disruption effectof orientation change

EXPERIMENT 3

In Experiment 1 (and also Experiments 1Bndash1E seeTable 1) we demonstrated that selective attention to onedimension of a stimulus (location) fails to filter outchanges in another dimension (orientation) if there aremultiple elongated items This raises the question aboutwhether the influence of orientation change is completelystimulus driven or whether it can be modulated by top-down attention Studies directly addressing the relationbetween selective attention and perceptual grouping haveshown that on the one hand the spread of attention is af-fected by perceptual grouping (Egly Driver amp Rafal1994 Lavie amp Driver 1996 Vecera amp Farah 1994)whereas on the other hand top-down attention influencesperceptual grouping (Peterson amp Gibson 1994a 1994b)Because perceptual grouping by line proximity appearsto occur obligatorily it is unclear whether it can be influ-enced by selective attention In this experiment we tested

the effect of selectively attending to one group of objectsover another group and measured the disruption of loca-tion change detection produced by orientation change ofthe attended versus the ignored group Figure 4 (inset)shows an example of a display

Each display contained two sets of itemsmdashred dotswith an interposing red line segment and green dots withan interposing green line segmentmdashrandomly intermixedon a 10 10 invisible matrix The subjects were in-structed in different blocks to attend either to the reditems or to the green items and to perform location changedetection of the attended group of items To test the ef-fect of selective attention we independently varied theprobability of orientation change for the attended and theignored sets If subjects can effectively attend to the in-structed group of items and if selective attention modu-lates which items enter perceptual grouping then orien-tation changes of the attended group should have a largereffect than do orientation changes of the ignored groupHowever if the influence of orientation changes is com-pletely stimulus driven we may not observe an effect ofselective attention

MethodSubjects Seventeen observers participated in this experimentMaterials Each display contained eight red items and eight

green items randomly intermixed on a 10 10 invisible matrix(19ordm 19deg) Each item was a filled dot (04ordm 04ordm) interposed witha line segment (12ordm 12ordm) that had one of four possible orienta-tions (0ordm 45ordm 90ordm or 135ordm)

Procedure The subjects were tested in 10 practice trials and 4blocks of experimental trials containing 48 trials each Before eachblock they were instructed to attend either to the green or to the red

Figure 4 The results from Experiment 3 A sample display is shown in theinset of the figure Red (shown as black items on this figure) and green (shownas white items on this figure) items were randomly intermixed on the displayError bars indicate standard error of between-subjects variation

Neither set Distractor set Target set Both setsOrientation change

1

95

9

85

8

75

7

PERCEPTUAL GROUPING AND CHANGE DETECTION 451

items and to perform a location change detection on the filled dotsEach trial started with a 400-msec fixation point followed by amemory display (eight red items and eight green items) The mem-ory display was presented for 400 msec and then was erased Aftera blank interval of 1 sec a probe display was presented until a re-sponse was made The probe display also contained eight red andeight green items Half of the time one of the attended items changedits location to a previously blank location and half of the time theattended items maintained their locations The ignored items neverchanged locations The subjects were asked to press a right key ifthey detected a location change and a left key otherwise They weretold to ignore the oriented lines and their orientation changes Theattended items changed their orientations on 50 of the trials Fur-thermore the ignored items also changed their orientations on 50of the trials

All the factors tested in this experiment were independently ma-nipulated Thus the subjects were tested in a total of 192 experi-mental trials which can be broken down as follows 2 attended col-ors (red vs green) 2 location changes (change vs no change) 2 attended itemsrsquo orientations (change vs no change) 2 ignoreditemsrsquo orientations (change vs no change) 12 cases

ResultsWe pooled data across blocks of attending to red and

blocks of attending to green and measured A separatelyfor four conditions both attended and ignored groupsmaintained their orientations (both same) ignored groupchanged orientations (ignored different) attended groupchanged orientations (attended different) and both groupschanged orientations (both different) Figure 4 shows theresults

An ANOVA on attended group and ignored group re-vealed a signif icant main effect of attended group[F(116) 578 p 029] showing lowered A for lo-cation change detection when the attended group of itemschanged orientations The main effect of ignored groupwas not significant [F(116) 110 p 30] suggest-ing that performance was not disrupted by orientationchanges in the ignored group The interaction betweenattended group and ignored group was not significant[F(116) 241 p 14] Planned contrasts showed thatorientation change in the attended group alone was suf-ficient to disrupt performance [t (16) 247 p 05]Nonetheless orientation change in the ignored groupalone produced a marginally significant reduction in per-formance [t (16) 222 p 081] This could be causedby attention leaking to the ignored items or by a stimulus-driven effect of obligatory grouping of every item on thedisplay Thus even though this experiment did not allowus to completely rule out bottom-up effects of orientationchange on location change detection it provided clear ev-idence that such effects were significantly modulated byselective attention

EXPERIMENT 4

Two factors jointly contribute to the effect of orienta-tion change on location change detection First the spa-tial relationship among items is obligatorily encoded inthe representation of multiple locations (Jiang et al2000) Second when constructing the global configura-tion subjects are unable to extract just the pattern formed

by the dots Instead the imaginary contour formed bythe elongated objects becomes part of the global patternwhich changes when the objects rotate In Experiment 2we tried to disrupt the representation of the global pat-tern by connecting the center of the dots or by present-ing a regular grid that served as an external frame of ref-erence to represent individual dots This largely reducedthe orientation change effect

In this experiment we further eliminated the need toencode the global configuration by informing the sub-jects about which single item might change location1The informative cue serves to narrow the focus of spatialattention to a single location removing the necessity torepresent all the items and their configuration If globalshape processing is partly responsible for the disruptioneffect then no disruption from orientation is expectedwhen subjects focus on a single item

MethodSubjects Six observers were testedMaterials Each display contained eight dots that were inter-

posed by a short line segment (see Experiment 1 and Figure 1) Thefirst display was presented for 150 msec and was then erased Onesecond later another display was presented until a response wasmade The first display was presented briefly to eliminate eyemovement

Design The subjects were tested in two conditions diffuse at-tention and focal attention (Figure 5) In the diffuse attention con-dition the first display contained eight black dots and the seconddisplay contained one black dot and seven white dots The subjectswere asked to decide whether or not the black dot on the second dis-play was at one of the previous eight locations Because they had tomonitor all the dots on the first display attention was diffuse so thesubjects would have needed to encode the individual locations andtheir global configuration In the focal attention condition the firstdisplay contained one black dot and seven white dots as did the sec-ond display The subjects were asked to decide whether the blackdot on the second display was at the same location as the one on thefirst display Attention was narrow because only a single locationneeded to be extracted and monitored from the first display andthus there was no need to encode the global configuration Figure 5shows an example of the display

The subjects were tested in 20 practice trials and 160 experi-mental trials These included a factorial design of three factors ex-tent of spatial attention (diffuse vs focal) location change (samevs different) and orientation change (same vs different) An ori-entation change meant that all items rotated by 90ordm including theitem(s) that the subjects were monitoring

Results and DiscussionThe results are shown in Figure 5 We calculated Aas

well as mean response time (RT) from each subjectrsquos me-dian RT (for correct trials only) An ANOVA on atten-tion and orientation change showed that performancewas better when the subjects monitored one locationthan when they monitored eight [F(15) 3959 p 001] and when the orientation of the irrelevant line seg-ments stayed the same [F(15) 1281 p 016] Therewas also a significant interaction between set size andorientation change [F(15) 1872 p 008] suggest-ing that the effect of orientation change was modulatedby how diffuse spatial attention was Orientation changedisrupted performance only when the subjects attended

452 JIANG CHUN AND OLSON

to all locations [t (5) 434 p 007] but not when theyfocused on one location [t (5) 099 p 35]

A similar pattern of results is seen in RTs An ANOVAshowed significant effects of set size [F(15) 2693 p 003] and orientation change [F(15) 3983 p 001]and a significant interaction [F(15) 944 p 03] Ori-entation change lengthened RTs when the subjects moni-tored all locations [t(5) 776 p 001] but not whenthey focused on one location [t(5) 132 p 20]

GENERAL DISCUSSION

This study provides a compelling demonstration thatthe perceptual grouping of individual items can signifi-cantly affect change detection even when subjects areinstructed to ignore the grouping When subjects had tofocus on change detection of one dimension (the spatiallocation of elongated items) they were unable to ignorechanges in another dimension (the orientations of theitems) We believe that this is because changes in the ori-

entations of elongated objects altered their global per-ceptual organization This disruption can be reduced byan invariant frame of reference such as a regularly spacedbackground grid (Experiment 2A) by actively usingcolor feature cues to ignore the group of items that un-derwent orientation changes (Experiment 3) or by nar-rowing the focus of attention to a single item (Experi-ment 4) However the presence of constant informationwas not always sufficient (Experiment 1) and the taskdemand to ignore orientation change of the attended setof items was not always effective

The disruption of location change detection by orien-tation change is the outcome of two interrelated pro-cesses First when multiple locations need to be retainedbriefly the visual system does not simply encode each in-dividual spatial location in an egocentric or environment-based frame of reference Instead the pattern formed byall the elements is obligatorily encoded and retained Achange in the global configuration of items severely dis-rupts change detection of individual locations (Jiang

Figure 5 Sample displays and results from Experiment 4 The subjects monitored the lo-cations of the black dots Error bars indicate the standard error of the difference betweensame orientation and different orientation

Set size = 8 Diffuse Set size = 1 Focal

1

9

8

7

6

5

750

700

650

600

5501 8 1 8

Same Orientation

Different Orientation

Attended set size Attended set size

RT

(m

sec)

Same Orientation

Different Orientation

PERCEPTUAL GROUPING AND CHANGE DETECTION 453

et al 2000 Santa 1977) Configural encoding is modu-lated by attention Only items that are actively attendedbecome part of the configuration (Jiang et al 2000) Asa result changes to irrelevant locations are negligible(Experiments 3 and 4)

Perceptual grouping which is related to configural pro-cessing influences how a configuration may be formedThus manipulations that might change the perceived con-figuration can potentially disrupt the representation of lo-cations Under many conditions selective attention canoverride the potential disruption produced by irrelevantchanges For example differences in color groupingfrom memory to probe displays were negligible duringlocation change detection This suggests that perceptualgrouping by color does not influence the spatial config-uration of items The special case that cannot be disre-garded is the orientation change in the long axis of elon-gated objects even when the centers of these objectswere clearly demarcated

Configural encoding alone cannot explain the effectsof orientation change This is because the configurationformed by the dots remained the same across the two dis-plays The results can be accounted for only if the con-figuration included not just the center dots but also thelong axes Orientation change alone also fails to explainthe disruption effect because orientation change of asingle item (Experiment 4) irrelevant items (Experi-ment 3) or items encoded within an environment-basedframe of reference (Experiment 2A) did not influencechange detection of locations Such effects thereforemust arise from the interaction among elongated objectsin multi-element displays That is the relative spatial lo-cations are no longer preserved when the long axes ofthese objects are rotated

Although we did not test every kind of groupingchange that might influence change detection of loca-tions the analysis above suggests that only groupingcues that influence the relative spatial location betweenitems will have an effect Grouping cues that affect sim-ilarity without changing perceived proximity such ascolor grouping do not influence location change detec-tion On the basis of this logic the present paradigm pro-vides a tool to quantify whether certain grouping cuesinfluence the perception of spatial locations

In conclusion our study provides further support thatitems are represented in a relational manner in changedetection (Jiang et al 2000) Perceptual grouping be-tween items can affect how each item is representedeven when the grouping is task irrelevant Whether ornot grouping defined by other kinds of visual features isalso represented in change detection remains to be seen

REFERENCES

Donaldson W (1993) Accuracy of d and A as estimates of sensitiv-ity Bulletin of the Psychonomic Society 31 271-274

Egly R Driver J amp Rafal R (1994) Shifting visual attention be-tween objects and locations Evidence from normal and parietal-lesion patients Journal of Experimental Psychology General 123161-177

Grier J B (1971) Nonparametric indexes for sensitivity and biasComputing formulas Psychological Bulletin 75 424-429

Hunt S M J (1994) MacProbe A Macintosh-based experimentersworkstation for the cognitive sciences Behavior Research MethodsInstruments amp Computers 26 345-351

Jiang Y Olson I R amp Chun M M (2000) Organization of visualshort-term memory Journal of Experimental Psychology LearningMemory amp Cognition 26 683-702

Lavie N amp Driver J (1996) On the spatial extent of attention inobject-based visual selection Perception amp Psychophysics 58 1238-1251

Luck S J amp Vogel E K (1997 November) The capacity of visualworking memory for features and conjunctions Nature 390 279-281

Palmer S E (1999) Vision science Photons to phenomenologyCambridge MA MIT Press

Pashler H (1988) Familiarity and visual change detection Percep-tion amp Psychophysics 44 369-378

Peterson M A amp Gibson B S (1994a) Must shape recognition fol-low figurendashground organization An assumption in peril Psycho-logical Science 5 253-259

Peterson M A amp Gibson B S (1994b) Object recognition contri-butions to figurendashground organization Operations on outlines andsubjective contours Perception amp Psychophysics 56 551-564

Phillips W A (1974) On the distinction between sensory storage andshort-term visual memory Perception amp Psychophysics 16 283-290

Rensink R A (2002) Change detection Annual Review of Psychol-ogy 53 245-277

Rensink R A ORegan J K amp Clark J J (1997) To see or not tosee The need for attention to perceive changes in scenes Psycho-logical Science 8 368-373

Santa J L (1977) Spatial transformations of words and picturesJournal of Experimental Psychology Human Learning amp Memory3 418-427

Simons D J amp Levin D T (1997) Change blindness Trends in Cog-nitive Sciences 1 261-267

Tulving E (1974) Cue-dependent forgetting American Scientist 6274-82

Vecera S P amp Farah M J (1994) Does visual attention select ob-jects or locations Journal of Experimental Psychology General123 146-160

Woodman G F Vecera S P amp Luck S J (2003) Perceptual orga-nization influences visual working memory Psychonomic Bulletin ampReview 10 80-87

NOTE

1 We thank Robert Melara for suggesting this manipulation

(Manuscript received January 10 2003revision accepted for publication August 25 2003)

PERCEPTUAL GROUPING AND CHANGE DETECTION 447

nization (grouping) is preserved when these items main-tain their colors across frames but is changed if some ofthe red items swap colors with some of the green itemsNonetheless if subjects are asked to remember the loca-tions of all the items then location change detection isunaffected by such color swapping (Jiang et al 2000)Thus it appears that if color grouping is relevant to thetask then the target group is effectively selected andstored in VSTM but if it is irrelevant to the task thenchange detection of locations can proceed independentlyof changes in the perceptual organization of the display

The purpose of our present study was to demonstratethat some types of perceptual grouping cues that are ir-relevant to the task cannot be effectively ignored in changedetection We presented subjects with two dot arrays sep-arated by a brief interstimulus interval of 1 sec and thesubjects were required to remember the locations ofthese dots and to judge whether the two arrays occupiedidentical locations or whether there was a change in onelocation Using these displays we have previously shownthat change detection of dot locations was unaffected bythe color change of these items (Jiang et al 2000) Inthe present study we added a short line segment inter-posing each dot From the memory to the probe displaythese line segments either maintained their orientationor changed orientation A schematic sample of an orien-tation change is illustrated in Figure 1

Note that in this design the locations of the dots wererelevant whereas the orientations of the line segmentswere not Nonetheless elongated lines tend to group byspatial proximity The change in their orientations pro-duced a change in the proximity relations and hence in-

duced changes in perceptual grouping Can irrelevantperceptual grouping always be ignored in change detec-tion of item locations

EXPERIMENT 1

MethodSubjects Ten observers were tested in Experiment 1 The sub-

jects were recruited from Yale University Vanderbilt Universityand Harvard University Their ages ranged from 18 to 30 years Allthe subjects signed an informed consent form before the test andwere fully debriefed after the experiment They had normal orcorrected-to-normal visual acuity and normal color vision

Procedure Each trial started with a 500-msec white fixation point(03ordm 03ordm) which was followed by an initial display containingeight elements in randomly selected cells in an invisible 8 8 ma-trix that subtended 175ordm 175ordm Each item was positioned at thecenter of a cell The initial display was presented for 400 msec fol-lowed by a blank display of 1000 msec Next the probe display con-taining eight elements was presented Each element was a black dot(04ordm 04ordm) with a white line segment (12ordm 02ordm) interposed at itscenter On 50 of the trials all of the dots maintained their locationsfrom the memory to the probe display On the other 50 of the trialsone dot was randomly selected from the eight and was relocated to apreviously unoccupied cell The observers were required to press oneof two keys to report whether they detected a location change Theywere instructed that the location of an item was indicated by the blackdot and they should ignore the white line elements

In addition to location changes each line segment either main-tained its initial randomly chosen orientation or changed its orien-tation by 45ordmndash90ordm (with 50 probability) Each subject was testedin 12 practice and 80 experimental trials (80 2 location [changevs nonchange] 2 orientation [change vs nonchange] 20 cases)

Equipment The experiment was programmed using MacProbe188 (Hunt 1994) The observers were tested individually in a roomwith normal interior lighting They sat at an unrestricted distance

Time

Probe displayuntil response

Interstimulusinterval 1000 msec

Memory display400 msec

Figure 1 A schematic example of the displays used in Experiment 1 This ex-ample shows a trial in which a dot changed its location and the line segmentsall changed orientations Not shown are control trials in which the line seg-ments maintained their orientations

448 JIANG CHUN AND OLSON

from the computer screen of about 57 cm at which distance 1 cmcorresponded to 1ordm of visual angle

Data analysis In this study we calculated A as a measure of thesubjects sensitivity (Grier 1971) We also measured percent cor-rect and d The overall pattern of results were the same whether Apercent correct or d was used A was preferred as a measure ofmemory accuracy (Donaldson 1993)

ResultsMean A for change detection of dot location was 91

when the orientations of the interposing lines did notchange and was 76 when they did change This differ-ence was statistically significant [t(9) 348 p 007]Thus change detection of locations was significantly im-paired by orientation change of irrelevant line segments

DiscussionIn change detection of dot locations the subjects were

unable to ignore orientation change of interposing linesegments This suggests that at least some contextualmismatch between encoding and retrieval irrelevant tothe critical dimension of the task could not be ignored

We performed further experiments (Experiments 1Bndash1J) in order to clarify the conditions under which irrele-vant orientation changes could and could not be ignoredTable 1 summarizes the results These data ruled outsome explanations of the disruption effect observed inExperiment 1 For example (1) item rotation in generaldid not produce disruption in location change detectionas long as the item was not elongated (eg gratings andcross patterns) and (2) the amount of transient changeswas not critical because the rotation of cross patterns ledto as much (or more) transient change but did not disrupt

performance The fact that disruption was significantwhen the retention interval was only 50 msec also sug-gests that the effect is tied to the perception of the stim-uli and is not just a property of VSTM retention In sumit appears that orientation changes in the long axis ofelongated objects were critical for the disruption of lo-cation change detection

Such disruption can be accounted for by the mismatchin perceptual grouping between the memory and theprobe displays Items in an array are not represented in-dividually but relationally Orientation change in elon-gated objects altered the global organization of the itemsFigure 2 illustrates how the global organization of elon-gated items is affected by their orientations Whereas thelines on the left panel tend to be grouped horizontallyowing to spatial proximity (Palmer 1999) after a 90ordm ro-tation the lines on the right panel tend to be grouped ver-tically even though the center locations of each item didnot change

If subjects are provided with an additional explicitframe of reference that is constant across changes in ori-entation then grouping by proximity should play a smallerrole The next experiment tests this hypothesis

EXPERIMENT 2

Experiment 2 tested whether an added constant refer-ence frame would reduce the disruption effect observedin Experiment 1 This additional reference frame wasprovided in two ways Line stimuli were presented withina regularly spaced visible grid (Experiment 2A) or thecenters of line stimuli were connected by chromatic links

Table 1Location Change Detection (A) Using Various Stimuli

Type of Item Change From A With A WithoutExperiment Stimuli Memory to Probe Displays Change Change N p Level

1B Rotation 73 87 7 006ISI 1000 msec

1C Rotation 83 98 7 002ISI 50 msec

1D Addition or deletion 81 88 8 005of line segments

1E Length change 88 95 6 007Same subjects Rotation 73 94 001

1F Rotation 88 88 11 50

1G Rotation 86 88 10 35

1H Color change 88 89 7 50

1I Shape change 91 90 7 50

1J Size change 81 84 7 25

NotemdashRanges of A from 5 to 10where 5 corresponds to chance performance and 10 correspondsto perfect performance With comparable amount of end point changes rotation produced a largerdisruption effect than length change did

PERCEPTUAL GROUPING AND CHANGE DETECTION 449

(Experiment 2B) Rotations of line stimuli orientationdid not affect the location of each item within the gridand the rotations did not change the shape of the chro-matic links Thus the regular grid or the links providedconstant information that was unaffected by line orien-tation change

The constancy provided by the reference frames mighthelp subjects ignore orientation changes However it isnot obvious whether such constant invariant cues aresufficient to reduce or remove the disruption effect Infact Experiment 1 showed that the presence of invariantinformation was not always sufficient When dots werepresented at the center of each line rotating the line seg-ments did not change the position of these salient dots(see Figure 1) yet the subjects could not ignore the ori-entation change In fact the invariant central dots failedto reduce the disruption Moreover unpublished datafrom our lab have revealed the same amount of disrup-tion whether the line centers were marked or not It istherefore of interest to find out whether other types ofcues such as the presence of a regular grid might pro-vide a constant reference frame that can reduce or elim-inate the disruption effect

MethodExperiment 2A Sixteen observers were tested Each observer

performed 12 practice and 256 experimental trials Two types ofstimuli were tested line arrays without an external background gridand line arrays appearing within a regularly spaced grid As in Ex-periment 1 we varied line orientation constancy from memory toprobe displays and also varied the presence or absence of one loca-tion change Ten observers were tested in a blocked design in whichthe presence or absence of the grid were tested in separate blocksand six were tested in a mixed design The results were pooledacross these two groups because the pattern of performance wasunaffected by this design Each display contained 12 items in het-erogeneous orientations

Experiment 2B Eight observers performed 12 practice and 256experimental trials The design of this experiment was identical tothat of Experiment 2A except that we replaced the regularly spacedgrid with a connect-the-dot chromatic grid that linked the centersof all the lines The two types of displays (lines with or withoutchromatic links) were tested in separate blocks The order of theblocks (ABBA or BAAB) was counterbalanced across observersEach display contained eight items in homogeneous orientations

ResultsFigure 3 plots A of location change detection as a

function of item rotation and grouping cues For Exper-iment 2A a repeated measures analysis of variance(ANOVA) showed a significant main effect of line ori-entation change [F(115) 1211 p 003] and a sig-nificant interaction between orientation change and thepresence or absence of background grid [F(115) 720p 017] The main effect of background grid was not sig-nificant [F(115) 166 p 20] Specifically orienta-tion change produced a significant disruption on changedetection when the lines were presented without the back-ground grid [t (15) 445 p 001] In contrast orien-tation change had no effect on performance when thelines were presented on a regularly spaced backgroundgrid [t (15) 139 p 15] Thus the presence of abackground grid eliminated the disruption effect pro-duced by line orientation change

Figure 2 Change in the orientation of the long axis of an itemleads to a change in perceptual grouping

Figure 3 The results from Experiment 2 Error bars indicate standard error ofbetween-subjects variation

450 JIANG CHUN AND OLSON

For Experiment 2B an ANOVA revealed a significantmain effect of line orientation change [F(17) 3520p 001] a significant main effect of the presence orabsence of chromatic links [F(17) 3060 p 001]and a significant interaction between orientation changeand chromatic links [F(17) 1649 p 005] Pairwiset tests showed that orientation change was disruptiveboth when the chromatic links were absent (p 001)and when they were present (p 002) However thesignificant interaction indicated that the presence of aconstant chromatic link attenuated the disruption effectof orientation change

EXPERIMENT 3

In Experiment 1 (and also Experiments 1Bndash1E seeTable 1) we demonstrated that selective attention to onedimension of a stimulus (location) fails to filter outchanges in another dimension (orientation) if there aremultiple elongated items This raises the question aboutwhether the influence of orientation change is completelystimulus driven or whether it can be modulated by top-down attention Studies directly addressing the relationbetween selective attention and perceptual grouping haveshown that on the one hand the spread of attention is af-fected by perceptual grouping (Egly Driver amp Rafal1994 Lavie amp Driver 1996 Vecera amp Farah 1994)whereas on the other hand top-down attention influencesperceptual grouping (Peterson amp Gibson 1994a 1994b)Because perceptual grouping by line proximity appearsto occur obligatorily it is unclear whether it can be influ-enced by selective attention In this experiment we tested

the effect of selectively attending to one group of objectsover another group and measured the disruption of loca-tion change detection produced by orientation change ofthe attended versus the ignored group Figure 4 (inset)shows an example of a display

Each display contained two sets of itemsmdashred dotswith an interposing red line segment and green dots withan interposing green line segmentmdashrandomly intermixedon a 10 10 invisible matrix The subjects were in-structed in different blocks to attend either to the reditems or to the green items and to perform location changedetection of the attended group of items To test the ef-fect of selective attention we independently varied theprobability of orientation change for the attended and theignored sets If subjects can effectively attend to the in-structed group of items and if selective attention modu-lates which items enter perceptual grouping then orien-tation changes of the attended group should have a largereffect than do orientation changes of the ignored groupHowever if the influence of orientation changes is com-pletely stimulus driven we may not observe an effect ofselective attention

MethodSubjects Seventeen observers participated in this experimentMaterials Each display contained eight red items and eight

green items randomly intermixed on a 10 10 invisible matrix(19ordm 19deg) Each item was a filled dot (04ordm 04ordm) interposed witha line segment (12ordm 12ordm) that had one of four possible orienta-tions (0ordm 45ordm 90ordm or 135ordm)

Procedure The subjects were tested in 10 practice trials and 4blocks of experimental trials containing 48 trials each Before eachblock they were instructed to attend either to the green or to the red

Figure 4 The results from Experiment 3 A sample display is shown in theinset of the figure Red (shown as black items on this figure) and green (shownas white items on this figure) items were randomly intermixed on the displayError bars indicate standard error of between-subjects variation

Neither set Distractor set Target set Both setsOrientation change

1

95

9

85

8

75

7

PERCEPTUAL GROUPING AND CHANGE DETECTION 451

items and to perform a location change detection on the filled dotsEach trial started with a 400-msec fixation point followed by amemory display (eight red items and eight green items) The mem-ory display was presented for 400 msec and then was erased Aftera blank interval of 1 sec a probe display was presented until a re-sponse was made The probe display also contained eight red andeight green items Half of the time one of the attended items changedits location to a previously blank location and half of the time theattended items maintained their locations The ignored items neverchanged locations The subjects were asked to press a right key ifthey detected a location change and a left key otherwise They weretold to ignore the oriented lines and their orientation changes Theattended items changed their orientations on 50 of the trials Fur-thermore the ignored items also changed their orientations on 50of the trials

All the factors tested in this experiment were independently ma-nipulated Thus the subjects were tested in a total of 192 experi-mental trials which can be broken down as follows 2 attended col-ors (red vs green) 2 location changes (change vs no change) 2 attended itemsrsquo orientations (change vs no change) 2 ignoreditemsrsquo orientations (change vs no change) 12 cases

ResultsWe pooled data across blocks of attending to red and

blocks of attending to green and measured A separatelyfor four conditions both attended and ignored groupsmaintained their orientations (both same) ignored groupchanged orientations (ignored different) attended groupchanged orientations (attended different) and both groupschanged orientations (both different) Figure 4 shows theresults

An ANOVA on attended group and ignored group re-vealed a signif icant main effect of attended group[F(116) 578 p 029] showing lowered A for lo-cation change detection when the attended group of itemschanged orientations The main effect of ignored groupwas not significant [F(116) 110 p 30] suggest-ing that performance was not disrupted by orientationchanges in the ignored group The interaction betweenattended group and ignored group was not significant[F(116) 241 p 14] Planned contrasts showed thatorientation change in the attended group alone was suf-ficient to disrupt performance [t (16) 247 p 05]Nonetheless orientation change in the ignored groupalone produced a marginally significant reduction in per-formance [t (16) 222 p 081] This could be causedby attention leaking to the ignored items or by a stimulus-driven effect of obligatory grouping of every item on thedisplay Thus even though this experiment did not allowus to completely rule out bottom-up effects of orientationchange on location change detection it provided clear ev-idence that such effects were significantly modulated byselective attention

EXPERIMENT 4

Two factors jointly contribute to the effect of orienta-tion change on location change detection First the spa-tial relationship among items is obligatorily encoded inthe representation of multiple locations (Jiang et al2000) Second when constructing the global configura-tion subjects are unable to extract just the pattern formed

by the dots Instead the imaginary contour formed bythe elongated objects becomes part of the global patternwhich changes when the objects rotate In Experiment 2we tried to disrupt the representation of the global pat-tern by connecting the center of the dots or by present-ing a regular grid that served as an external frame of ref-erence to represent individual dots This largely reducedthe orientation change effect

In this experiment we further eliminated the need toencode the global configuration by informing the sub-jects about which single item might change location1The informative cue serves to narrow the focus of spatialattention to a single location removing the necessity torepresent all the items and their configuration If globalshape processing is partly responsible for the disruptioneffect then no disruption from orientation is expectedwhen subjects focus on a single item

MethodSubjects Six observers were testedMaterials Each display contained eight dots that were inter-

posed by a short line segment (see Experiment 1 and Figure 1) Thefirst display was presented for 150 msec and was then erased Onesecond later another display was presented until a response wasmade The first display was presented briefly to eliminate eyemovement

Design The subjects were tested in two conditions diffuse at-tention and focal attention (Figure 5) In the diffuse attention con-dition the first display contained eight black dots and the seconddisplay contained one black dot and seven white dots The subjectswere asked to decide whether or not the black dot on the second dis-play was at one of the previous eight locations Because they had tomonitor all the dots on the first display attention was diffuse so thesubjects would have needed to encode the individual locations andtheir global configuration In the focal attention condition the firstdisplay contained one black dot and seven white dots as did the sec-ond display The subjects were asked to decide whether the blackdot on the second display was at the same location as the one on thefirst display Attention was narrow because only a single locationneeded to be extracted and monitored from the first display andthus there was no need to encode the global configuration Figure 5shows an example of the display

The subjects were tested in 20 practice trials and 160 experi-mental trials These included a factorial design of three factors ex-tent of spatial attention (diffuse vs focal) location change (samevs different) and orientation change (same vs different) An ori-entation change meant that all items rotated by 90ordm including theitem(s) that the subjects were monitoring

Results and DiscussionThe results are shown in Figure 5 We calculated Aas

well as mean response time (RT) from each subjectrsquos me-dian RT (for correct trials only) An ANOVA on atten-tion and orientation change showed that performancewas better when the subjects monitored one locationthan when they monitored eight [F(15) 3959 p 001] and when the orientation of the irrelevant line seg-ments stayed the same [F(15) 1281 p 016] Therewas also a significant interaction between set size andorientation change [F(15) 1872 p 008] suggest-ing that the effect of orientation change was modulatedby how diffuse spatial attention was Orientation changedisrupted performance only when the subjects attended

452 JIANG CHUN AND OLSON

to all locations [t (5) 434 p 007] but not when theyfocused on one location [t (5) 099 p 35]

A similar pattern of results is seen in RTs An ANOVAshowed significant effects of set size [F(15) 2693 p 003] and orientation change [F(15) 3983 p 001]and a significant interaction [F(15) 944 p 03] Ori-entation change lengthened RTs when the subjects moni-tored all locations [t(5) 776 p 001] but not whenthey focused on one location [t(5) 132 p 20]

GENERAL DISCUSSION

This study provides a compelling demonstration thatthe perceptual grouping of individual items can signifi-cantly affect change detection even when subjects areinstructed to ignore the grouping When subjects had tofocus on change detection of one dimension (the spatiallocation of elongated items) they were unable to ignorechanges in another dimension (the orientations of theitems) We believe that this is because changes in the ori-

entations of elongated objects altered their global per-ceptual organization This disruption can be reduced byan invariant frame of reference such as a regularly spacedbackground grid (Experiment 2A) by actively usingcolor feature cues to ignore the group of items that un-derwent orientation changes (Experiment 3) or by nar-rowing the focus of attention to a single item (Experi-ment 4) However the presence of constant informationwas not always sufficient (Experiment 1) and the taskdemand to ignore orientation change of the attended setof items was not always effective

The disruption of location change detection by orien-tation change is the outcome of two interrelated pro-cesses First when multiple locations need to be retainedbriefly the visual system does not simply encode each in-dividual spatial location in an egocentric or environment-based frame of reference Instead the pattern formed byall the elements is obligatorily encoded and retained Achange in the global configuration of items severely dis-rupts change detection of individual locations (Jiang

Figure 5 Sample displays and results from Experiment 4 The subjects monitored the lo-cations of the black dots Error bars indicate the standard error of the difference betweensame orientation and different orientation

Set size = 8 Diffuse Set size = 1 Focal

1

9

8

7

6

5

750

700

650

600

5501 8 1 8

Same Orientation

Different Orientation

Attended set size Attended set size

RT

(m

sec)

Same Orientation

Different Orientation

PERCEPTUAL GROUPING AND CHANGE DETECTION 453

et al 2000 Santa 1977) Configural encoding is modu-lated by attention Only items that are actively attendedbecome part of the configuration (Jiang et al 2000) Asa result changes to irrelevant locations are negligible(Experiments 3 and 4)

Perceptual grouping which is related to configural pro-cessing influences how a configuration may be formedThus manipulations that might change the perceived con-figuration can potentially disrupt the representation of lo-cations Under many conditions selective attention canoverride the potential disruption produced by irrelevantchanges For example differences in color groupingfrom memory to probe displays were negligible duringlocation change detection This suggests that perceptualgrouping by color does not influence the spatial config-uration of items The special case that cannot be disre-garded is the orientation change in the long axis of elon-gated objects even when the centers of these objectswere clearly demarcated

Configural encoding alone cannot explain the effectsof orientation change This is because the configurationformed by the dots remained the same across the two dis-plays The results can be accounted for only if the con-figuration included not just the center dots but also thelong axes Orientation change alone also fails to explainthe disruption effect because orientation change of asingle item (Experiment 4) irrelevant items (Experi-ment 3) or items encoded within an environment-basedframe of reference (Experiment 2A) did not influencechange detection of locations Such effects thereforemust arise from the interaction among elongated objectsin multi-element displays That is the relative spatial lo-cations are no longer preserved when the long axes ofthese objects are rotated

Although we did not test every kind of groupingchange that might influence change detection of loca-tions the analysis above suggests that only groupingcues that influence the relative spatial location betweenitems will have an effect Grouping cues that affect sim-ilarity without changing perceived proximity such ascolor grouping do not influence location change detec-tion On the basis of this logic the present paradigm pro-vides a tool to quantify whether certain grouping cuesinfluence the perception of spatial locations

In conclusion our study provides further support thatitems are represented in a relational manner in changedetection (Jiang et al 2000) Perceptual grouping be-tween items can affect how each item is representedeven when the grouping is task irrelevant Whether ornot grouping defined by other kinds of visual features isalso represented in change detection remains to be seen

REFERENCES

Donaldson W (1993) Accuracy of d and A as estimates of sensitiv-ity Bulletin of the Psychonomic Society 31 271-274

Egly R Driver J amp Rafal R (1994) Shifting visual attention be-tween objects and locations Evidence from normal and parietal-lesion patients Journal of Experimental Psychology General 123161-177

Grier J B (1971) Nonparametric indexes for sensitivity and biasComputing formulas Psychological Bulletin 75 424-429

Hunt S M J (1994) MacProbe A Macintosh-based experimentersworkstation for the cognitive sciences Behavior Research MethodsInstruments amp Computers 26 345-351

Jiang Y Olson I R amp Chun M M (2000) Organization of visualshort-term memory Journal of Experimental Psychology LearningMemory amp Cognition 26 683-702

Lavie N amp Driver J (1996) On the spatial extent of attention inobject-based visual selection Perception amp Psychophysics 58 1238-1251

Luck S J amp Vogel E K (1997 November) The capacity of visualworking memory for features and conjunctions Nature 390 279-281

Palmer S E (1999) Vision science Photons to phenomenologyCambridge MA MIT Press

Pashler H (1988) Familiarity and visual change detection Percep-tion amp Psychophysics 44 369-378

Peterson M A amp Gibson B S (1994a) Must shape recognition fol-low figurendashground organization An assumption in peril Psycho-logical Science 5 253-259

Peterson M A amp Gibson B S (1994b) Object recognition contri-butions to figurendashground organization Operations on outlines andsubjective contours Perception amp Psychophysics 56 551-564

Phillips W A (1974) On the distinction between sensory storage andshort-term visual memory Perception amp Psychophysics 16 283-290

Rensink R A (2002) Change detection Annual Review of Psychol-ogy 53 245-277

Rensink R A ORegan J K amp Clark J J (1997) To see or not tosee The need for attention to perceive changes in scenes Psycho-logical Science 8 368-373

Santa J L (1977) Spatial transformations of words and picturesJournal of Experimental Psychology Human Learning amp Memory3 418-427

Simons D J amp Levin D T (1997) Change blindness Trends in Cog-nitive Sciences 1 261-267

Tulving E (1974) Cue-dependent forgetting American Scientist 6274-82

Vecera S P amp Farah M J (1994) Does visual attention select ob-jects or locations Journal of Experimental Psychology General123 146-160

Woodman G F Vecera S P amp Luck S J (2003) Perceptual orga-nization influences visual working memory Psychonomic Bulletin ampReview 10 80-87

NOTE

1 We thank Robert Melara for suggesting this manipulation

(Manuscript received January 10 2003revision accepted for publication August 25 2003)

448 JIANG CHUN AND OLSON

from the computer screen of about 57 cm at which distance 1 cmcorresponded to 1ordm of visual angle

Data analysis In this study we calculated A as a measure of thesubjects sensitivity (Grier 1971) We also measured percent cor-rect and d The overall pattern of results were the same whether Apercent correct or d was used A was preferred as a measure ofmemory accuracy (Donaldson 1993)

ResultsMean A for change detection of dot location was 91

when the orientations of the interposing lines did notchange and was 76 when they did change This differ-ence was statistically significant [t(9) 348 p 007]Thus change detection of locations was significantly im-paired by orientation change of irrelevant line segments

DiscussionIn change detection of dot locations the subjects were

unable to ignore orientation change of interposing linesegments This suggests that at least some contextualmismatch between encoding and retrieval irrelevant tothe critical dimension of the task could not be ignored

We performed further experiments (Experiments 1Bndash1J) in order to clarify the conditions under which irrele-vant orientation changes could and could not be ignoredTable 1 summarizes the results These data ruled outsome explanations of the disruption effect observed inExperiment 1 For example (1) item rotation in generaldid not produce disruption in location change detectionas long as the item was not elongated (eg gratings andcross patterns) and (2) the amount of transient changeswas not critical because the rotation of cross patterns ledto as much (or more) transient change but did not disrupt

performance The fact that disruption was significantwhen the retention interval was only 50 msec also sug-gests that the effect is tied to the perception of the stim-uli and is not just a property of VSTM retention In sumit appears that orientation changes in the long axis ofelongated objects were critical for the disruption of lo-cation change detection

Such disruption can be accounted for by the mismatchin perceptual grouping between the memory and theprobe displays Items in an array are not represented in-dividually but relationally Orientation change in elon-gated objects altered the global organization of the itemsFigure 2 illustrates how the global organization of elon-gated items is affected by their orientations Whereas thelines on the left panel tend to be grouped horizontallyowing to spatial proximity (Palmer 1999) after a 90ordm ro-tation the lines on the right panel tend to be grouped ver-tically even though the center locations of each item didnot change

If subjects are provided with an additional explicitframe of reference that is constant across changes in ori-entation then grouping by proximity should play a smallerrole The next experiment tests this hypothesis

EXPERIMENT 2

Experiment 2 tested whether an added constant refer-ence frame would reduce the disruption effect observedin Experiment 1 This additional reference frame wasprovided in two ways Line stimuli were presented withina regularly spaced visible grid (Experiment 2A) or thecenters of line stimuli were connected by chromatic links

Table 1Location Change Detection (A) Using Various Stimuli

Type of Item Change From A With A WithoutExperiment Stimuli Memory to Probe Displays Change Change N p Level

1B Rotation 73 87 7 006ISI 1000 msec

1C Rotation 83 98 7 002ISI 50 msec

1D Addition or deletion 81 88 8 005of line segments

1E Length change 88 95 6 007Same subjects Rotation 73 94 001

1F Rotation 88 88 11 50

1G Rotation 86 88 10 35

1H Color change 88 89 7 50

1I Shape change 91 90 7 50

1J Size change 81 84 7 25

NotemdashRanges of A from 5 to 10where 5 corresponds to chance performance and 10 correspondsto perfect performance With comparable amount of end point changes rotation produced a largerdisruption effect than length change did

PERCEPTUAL GROUPING AND CHANGE DETECTION 449

(Experiment 2B) Rotations of line stimuli orientationdid not affect the location of each item within the gridand the rotations did not change the shape of the chro-matic links Thus the regular grid or the links providedconstant information that was unaffected by line orien-tation change

The constancy provided by the reference frames mighthelp subjects ignore orientation changes However it isnot obvious whether such constant invariant cues aresufficient to reduce or remove the disruption effect Infact Experiment 1 showed that the presence of invariantinformation was not always sufficient When dots werepresented at the center of each line rotating the line seg-ments did not change the position of these salient dots(see Figure 1) yet the subjects could not ignore the ori-entation change In fact the invariant central dots failedto reduce the disruption Moreover unpublished datafrom our lab have revealed the same amount of disrup-tion whether the line centers were marked or not It istherefore of interest to find out whether other types ofcues such as the presence of a regular grid might pro-vide a constant reference frame that can reduce or elim-inate the disruption effect

MethodExperiment 2A Sixteen observers were tested Each observer

performed 12 practice and 256 experimental trials Two types ofstimuli were tested line arrays without an external background gridand line arrays appearing within a regularly spaced grid As in Ex-periment 1 we varied line orientation constancy from memory toprobe displays and also varied the presence or absence of one loca-tion change Ten observers were tested in a blocked design in whichthe presence or absence of the grid were tested in separate blocksand six were tested in a mixed design The results were pooledacross these two groups because the pattern of performance wasunaffected by this design Each display contained 12 items in het-erogeneous orientations

Experiment 2B Eight observers performed 12 practice and 256experimental trials The design of this experiment was identical tothat of Experiment 2A except that we replaced the regularly spacedgrid with a connect-the-dot chromatic grid that linked the centersof all the lines The two types of displays (lines with or withoutchromatic links) were tested in separate blocks The order of theblocks (ABBA or BAAB) was counterbalanced across observersEach display contained eight items in homogeneous orientations

ResultsFigure 3 plots A of location change detection as a

function of item rotation and grouping cues For Exper-iment 2A a repeated measures analysis of variance(ANOVA) showed a significant main effect of line ori-entation change [F(115) 1211 p 003] and a sig-nificant interaction between orientation change and thepresence or absence of background grid [F(115) 720p 017] The main effect of background grid was not sig-nificant [F(115) 166 p 20] Specifically orienta-tion change produced a significant disruption on changedetection when the lines were presented without the back-ground grid [t (15) 445 p 001] In contrast orien-tation change had no effect on performance when thelines were presented on a regularly spaced backgroundgrid [t (15) 139 p 15] Thus the presence of abackground grid eliminated the disruption effect pro-duced by line orientation change

Figure 2 Change in the orientation of the long axis of an itemleads to a change in perceptual grouping

Figure 3 The results from Experiment 2 Error bars indicate standard error ofbetween-subjects variation

450 JIANG CHUN AND OLSON

For Experiment 2B an ANOVA revealed a significantmain effect of line orientation change [F(17) 3520p 001] a significant main effect of the presence orabsence of chromatic links [F(17) 3060 p 001]and a significant interaction between orientation changeand chromatic links [F(17) 1649 p 005] Pairwiset tests showed that orientation change was disruptiveboth when the chromatic links were absent (p 001)and when they were present (p 002) However thesignificant interaction indicated that the presence of aconstant chromatic link attenuated the disruption effectof orientation change

EXPERIMENT 3

In Experiment 1 (and also Experiments 1Bndash1E seeTable 1) we demonstrated that selective attention to onedimension of a stimulus (location) fails to filter outchanges in another dimension (orientation) if there aremultiple elongated items This raises the question aboutwhether the influence of orientation change is completelystimulus driven or whether it can be modulated by top-down attention Studies directly addressing the relationbetween selective attention and perceptual grouping haveshown that on the one hand the spread of attention is af-fected by perceptual grouping (Egly Driver amp Rafal1994 Lavie amp Driver 1996 Vecera amp Farah 1994)whereas on the other hand top-down attention influencesperceptual grouping (Peterson amp Gibson 1994a 1994b)Because perceptual grouping by line proximity appearsto occur obligatorily it is unclear whether it can be influ-enced by selective attention In this experiment we tested

the effect of selectively attending to one group of objectsover another group and measured the disruption of loca-tion change detection produced by orientation change ofthe attended versus the ignored group Figure 4 (inset)shows an example of a display

Each display contained two sets of itemsmdashred dotswith an interposing red line segment and green dots withan interposing green line segmentmdashrandomly intermixedon a 10 10 invisible matrix The subjects were in-structed in different blocks to attend either to the reditems or to the green items and to perform location changedetection of the attended group of items To test the ef-fect of selective attention we independently varied theprobability of orientation change for the attended and theignored sets If subjects can effectively attend to the in-structed group of items and if selective attention modu-lates which items enter perceptual grouping then orien-tation changes of the attended group should have a largereffect than do orientation changes of the ignored groupHowever if the influence of orientation changes is com-pletely stimulus driven we may not observe an effect ofselective attention

MethodSubjects Seventeen observers participated in this experimentMaterials Each display contained eight red items and eight

green items randomly intermixed on a 10 10 invisible matrix(19ordm 19deg) Each item was a filled dot (04ordm 04ordm) interposed witha line segment (12ordm 12ordm) that had one of four possible orienta-tions (0ordm 45ordm 90ordm or 135ordm)

Procedure The subjects were tested in 10 practice trials and 4blocks of experimental trials containing 48 trials each Before eachblock they were instructed to attend either to the green or to the red

Figure 4 The results from Experiment 3 A sample display is shown in theinset of the figure Red (shown as black items on this figure) and green (shownas white items on this figure) items were randomly intermixed on the displayError bars indicate standard error of between-subjects variation

Neither set Distractor set Target set Both setsOrientation change

1

95

9

85

8

75

7

PERCEPTUAL GROUPING AND CHANGE DETECTION 451

items and to perform a location change detection on the filled dotsEach trial started with a 400-msec fixation point followed by amemory display (eight red items and eight green items) The mem-ory display was presented for 400 msec and then was erased Aftera blank interval of 1 sec a probe display was presented until a re-sponse was made The probe display also contained eight red andeight green items Half of the time one of the attended items changedits location to a previously blank location and half of the time theattended items maintained their locations The ignored items neverchanged locations The subjects were asked to press a right key ifthey detected a location change and a left key otherwise They weretold to ignore the oriented lines and their orientation changes Theattended items changed their orientations on 50 of the trials Fur-thermore the ignored items also changed their orientations on 50of the trials

All the factors tested in this experiment were independently ma-nipulated Thus the subjects were tested in a total of 192 experi-mental trials which can be broken down as follows 2 attended col-ors (red vs green) 2 location changes (change vs no change) 2 attended itemsrsquo orientations (change vs no change) 2 ignoreditemsrsquo orientations (change vs no change) 12 cases

ResultsWe pooled data across blocks of attending to red and

blocks of attending to green and measured A separatelyfor four conditions both attended and ignored groupsmaintained their orientations (both same) ignored groupchanged orientations (ignored different) attended groupchanged orientations (attended different) and both groupschanged orientations (both different) Figure 4 shows theresults

An ANOVA on attended group and ignored group re-vealed a signif icant main effect of attended group[F(116) 578 p 029] showing lowered A for lo-cation change detection when the attended group of itemschanged orientations The main effect of ignored groupwas not significant [F(116) 110 p 30] suggest-ing that performance was not disrupted by orientationchanges in the ignored group The interaction betweenattended group and ignored group was not significant[F(116) 241 p 14] Planned contrasts showed thatorientation change in the attended group alone was suf-ficient to disrupt performance [t (16) 247 p 05]Nonetheless orientation change in the ignored groupalone produced a marginally significant reduction in per-formance [t (16) 222 p 081] This could be causedby attention leaking to the ignored items or by a stimulus-driven effect of obligatory grouping of every item on thedisplay Thus even though this experiment did not allowus to completely rule out bottom-up effects of orientationchange on location change detection it provided clear ev-idence that such effects were significantly modulated byselective attention

EXPERIMENT 4

Two factors jointly contribute to the effect of orienta-tion change on location change detection First the spa-tial relationship among items is obligatorily encoded inthe representation of multiple locations (Jiang et al2000) Second when constructing the global configura-tion subjects are unable to extract just the pattern formed

by the dots Instead the imaginary contour formed bythe elongated objects becomes part of the global patternwhich changes when the objects rotate In Experiment 2we tried to disrupt the representation of the global pat-tern by connecting the center of the dots or by present-ing a regular grid that served as an external frame of ref-erence to represent individual dots This largely reducedthe orientation change effect

In this experiment we further eliminated the need toencode the global configuration by informing the sub-jects about which single item might change location1The informative cue serves to narrow the focus of spatialattention to a single location removing the necessity torepresent all the items and their configuration If globalshape processing is partly responsible for the disruptioneffect then no disruption from orientation is expectedwhen subjects focus on a single item

MethodSubjects Six observers were testedMaterials Each display contained eight dots that were inter-

posed by a short line segment (see Experiment 1 and Figure 1) Thefirst display was presented for 150 msec and was then erased Onesecond later another display was presented until a response wasmade The first display was presented briefly to eliminate eyemovement

Design The subjects were tested in two conditions diffuse at-tention and focal attention (Figure 5) In the diffuse attention con-dition the first display contained eight black dots and the seconddisplay contained one black dot and seven white dots The subjectswere asked to decide whether or not the black dot on the second dis-play was at one of the previous eight locations Because they had tomonitor all the dots on the first display attention was diffuse so thesubjects would have needed to encode the individual locations andtheir global configuration In the focal attention condition the firstdisplay contained one black dot and seven white dots as did the sec-ond display The subjects were asked to decide whether the blackdot on the second display was at the same location as the one on thefirst display Attention was narrow because only a single locationneeded to be extracted and monitored from the first display andthus there was no need to encode the global configuration Figure 5shows an example of the display

The subjects were tested in 20 practice trials and 160 experi-mental trials These included a factorial design of three factors ex-tent of spatial attention (diffuse vs focal) location change (samevs different) and orientation change (same vs different) An ori-entation change meant that all items rotated by 90ordm including theitem(s) that the subjects were monitoring

Results and DiscussionThe results are shown in Figure 5 We calculated Aas

well as mean response time (RT) from each subjectrsquos me-dian RT (for correct trials only) An ANOVA on atten-tion and orientation change showed that performancewas better when the subjects monitored one locationthan when they monitored eight [F(15) 3959 p 001] and when the orientation of the irrelevant line seg-ments stayed the same [F(15) 1281 p 016] Therewas also a significant interaction between set size andorientation change [F(15) 1872 p 008] suggest-ing that the effect of orientation change was modulatedby how diffuse spatial attention was Orientation changedisrupted performance only when the subjects attended

452 JIANG CHUN AND OLSON

to all locations [t (5) 434 p 007] but not when theyfocused on one location [t (5) 099 p 35]

A similar pattern of results is seen in RTs An ANOVAshowed significant effects of set size [F(15) 2693 p 003] and orientation change [F(15) 3983 p 001]and a significant interaction [F(15) 944 p 03] Ori-entation change lengthened RTs when the subjects moni-tored all locations [t(5) 776 p 001] but not whenthey focused on one location [t(5) 132 p 20]

GENERAL DISCUSSION

This study provides a compelling demonstration thatthe perceptual grouping of individual items can signifi-cantly affect change detection even when subjects areinstructed to ignore the grouping When subjects had tofocus on change detection of one dimension (the spatiallocation of elongated items) they were unable to ignorechanges in another dimension (the orientations of theitems) We believe that this is because changes in the ori-

entations of elongated objects altered their global per-ceptual organization This disruption can be reduced byan invariant frame of reference such as a regularly spacedbackground grid (Experiment 2A) by actively usingcolor feature cues to ignore the group of items that un-derwent orientation changes (Experiment 3) or by nar-rowing the focus of attention to a single item (Experi-ment 4) However the presence of constant informationwas not always sufficient (Experiment 1) and the taskdemand to ignore orientation change of the attended setof items was not always effective

The disruption of location change detection by orien-tation change is the outcome of two interrelated pro-cesses First when multiple locations need to be retainedbriefly the visual system does not simply encode each in-dividual spatial location in an egocentric or environment-based frame of reference Instead the pattern formed byall the elements is obligatorily encoded and retained Achange in the global configuration of items severely dis-rupts change detection of individual locations (Jiang

Figure 5 Sample displays and results from Experiment 4 The subjects monitored the lo-cations of the black dots Error bars indicate the standard error of the difference betweensame orientation and different orientation

Set size = 8 Diffuse Set size = 1 Focal

1

9

8

7

6

5

750

700

650

600

5501 8 1 8

Same Orientation

Different Orientation

Attended set size Attended set size

RT

(m

sec)

Same Orientation

Different Orientation

PERCEPTUAL GROUPING AND CHANGE DETECTION 453

et al 2000 Santa 1977) Configural encoding is modu-lated by attention Only items that are actively attendedbecome part of the configuration (Jiang et al 2000) Asa result changes to irrelevant locations are negligible(Experiments 3 and 4)

Perceptual grouping which is related to configural pro-cessing influences how a configuration may be formedThus manipulations that might change the perceived con-figuration can potentially disrupt the representation of lo-cations Under many conditions selective attention canoverride the potential disruption produced by irrelevantchanges For example differences in color groupingfrom memory to probe displays were negligible duringlocation change detection This suggests that perceptualgrouping by color does not influence the spatial config-uration of items The special case that cannot be disre-garded is the orientation change in the long axis of elon-gated objects even when the centers of these objectswere clearly demarcated

Configural encoding alone cannot explain the effectsof orientation change This is because the configurationformed by the dots remained the same across the two dis-plays The results can be accounted for only if the con-figuration included not just the center dots but also thelong axes Orientation change alone also fails to explainthe disruption effect because orientation change of asingle item (Experiment 4) irrelevant items (Experi-ment 3) or items encoded within an environment-basedframe of reference (Experiment 2A) did not influencechange detection of locations Such effects thereforemust arise from the interaction among elongated objectsin multi-element displays That is the relative spatial lo-cations are no longer preserved when the long axes ofthese objects are rotated

Although we did not test every kind of groupingchange that might influence change detection of loca-tions the analysis above suggests that only groupingcues that influence the relative spatial location betweenitems will have an effect Grouping cues that affect sim-ilarity without changing perceived proximity such ascolor grouping do not influence location change detec-tion On the basis of this logic the present paradigm pro-vides a tool to quantify whether certain grouping cuesinfluence the perception of spatial locations

In conclusion our study provides further support thatitems are represented in a relational manner in changedetection (Jiang et al 2000) Perceptual grouping be-tween items can affect how each item is representedeven when the grouping is task irrelevant Whether ornot grouping defined by other kinds of visual features isalso represented in change detection remains to be seen

REFERENCES

Donaldson W (1993) Accuracy of d and A as estimates of sensitiv-ity Bulletin of the Psychonomic Society 31 271-274

Egly R Driver J amp Rafal R (1994) Shifting visual attention be-tween objects and locations Evidence from normal and parietal-lesion patients Journal of Experimental Psychology General 123161-177

Grier J B (1971) Nonparametric indexes for sensitivity and biasComputing formulas Psychological Bulletin 75 424-429

Hunt S M J (1994) MacProbe A Macintosh-based experimentersworkstation for the cognitive sciences Behavior Research MethodsInstruments amp Computers 26 345-351

Jiang Y Olson I R amp Chun M M (2000) Organization of visualshort-term memory Journal of Experimental Psychology LearningMemory amp Cognition 26 683-702

Lavie N amp Driver J (1996) On the spatial extent of attention inobject-based visual selection Perception amp Psychophysics 58 1238-1251

Luck S J amp Vogel E K (1997 November) The capacity of visualworking memory for features and conjunctions Nature 390 279-281

Palmer S E (1999) Vision science Photons to phenomenologyCambridge MA MIT Press

Pashler H (1988) Familiarity and visual change detection Percep-tion amp Psychophysics 44 369-378

Peterson M A amp Gibson B S (1994a) Must shape recognition fol-low figurendashground organization An assumption in peril Psycho-logical Science 5 253-259

Peterson M A amp Gibson B S (1994b) Object recognition contri-butions to figurendashground organization Operations on outlines andsubjective contours Perception amp Psychophysics 56 551-564

Phillips W A (1974) On the distinction between sensory storage andshort-term visual memory Perception amp Psychophysics 16 283-290

Rensink R A (2002) Change detection Annual Review of Psychol-ogy 53 245-277

Rensink R A ORegan J K amp Clark J J (1997) To see or not tosee The need for attention to perceive changes in scenes Psycho-logical Science 8 368-373

Santa J L (1977) Spatial transformations of words and picturesJournal of Experimental Psychology Human Learning amp Memory3 418-427

Simons D J amp Levin D T (1997) Change blindness Trends in Cog-nitive Sciences 1 261-267

Tulving E (1974) Cue-dependent forgetting American Scientist 6274-82

Vecera S P amp Farah M J (1994) Does visual attention select ob-jects or locations Journal of Experimental Psychology General123 146-160

Woodman G F Vecera S P amp Luck S J (2003) Perceptual orga-nization influences visual working memory Psychonomic Bulletin ampReview 10 80-87

NOTE

1 We thank Robert Melara for suggesting this manipulation

(Manuscript received January 10 2003revision accepted for publication August 25 2003)

PERCEPTUAL GROUPING AND CHANGE DETECTION 449

(Experiment 2B) Rotations of line stimuli orientationdid not affect the location of each item within the gridand the rotations did not change the shape of the chro-matic links Thus the regular grid or the links providedconstant information that was unaffected by line orien-tation change

The constancy provided by the reference frames mighthelp subjects ignore orientation changes However it isnot obvious whether such constant invariant cues aresufficient to reduce or remove the disruption effect Infact Experiment 1 showed that the presence of invariantinformation was not always sufficient When dots werepresented at the center of each line rotating the line seg-ments did not change the position of these salient dots(see Figure 1) yet the subjects could not ignore the ori-entation change In fact the invariant central dots failedto reduce the disruption Moreover unpublished datafrom our lab have revealed the same amount of disrup-tion whether the line centers were marked or not It istherefore of interest to find out whether other types ofcues such as the presence of a regular grid might pro-vide a constant reference frame that can reduce or elim-inate the disruption effect

MethodExperiment 2A Sixteen observers were tested Each observer

performed 12 practice and 256 experimental trials Two types ofstimuli were tested line arrays without an external background gridand line arrays appearing within a regularly spaced grid As in Ex-periment 1 we varied line orientation constancy from memory toprobe displays and also varied the presence or absence of one loca-tion change Ten observers were tested in a blocked design in whichthe presence or absence of the grid were tested in separate blocksand six were tested in a mixed design The results were pooledacross these two groups because the pattern of performance wasunaffected by this design Each display contained 12 items in het-erogeneous orientations

Experiment 2B Eight observers performed 12 practice and 256experimental trials The design of this experiment was identical tothat of Experiment 2A except that we replaced the regularly spacedgrid with a connect-the-dot chromatic grid that linked the centersof all the lines The two types of displays (lines with or withoutchromatic links) were tested in separate blocks The order of theblocks (ABBA or BAAB) was counterbalanced across observersEach display contained eight items in homogeneous orientations

ResultsFigure 3 plots A of location change detection as a

function of item rotation and grouping cues For Exper-iment 2A a repeated measures analysis of variance(ANOVA) showed a significant main effect of line ori-entation change [F(115) 1211 p 003] and a sig-nificant interaction between orientation change and thepresence or absence of background grid [F(115) 720p 017] The main effect of background grid was not sig-nificant [F(115) 166 p 20] Specifically orienta-tion change produced a significant disruption on changedetection when the lines were presented without the back-ground grid [t (15) 445 p 001] In contrast orien-tation change had no effect on performance when thelines were presented on a regularly spaced backgroundgrid [t (15) 139 p 15] Thus the presence of abackground grid eliminated the disruption effect pro-duced by line orientation change

Figure 2 Change in the orientation of the long axis of an itemleads to a change in perceptual grouping

Figure 3 The results from Experiment 2 Error bars indicate standard error ofbetween-subjects variation

450 JIANG CHUN AND OLSON

For Experiment 2B an ANOVA revealed a significantmain effect of line orientation change [F(17) 3520p 001] a significant main effect of the presence orabsence of chromatic links [F(17) 3060 p 001]and a significant interaction between orientation changeand chromatic links [F(17) 1649 p 005] Pairwiset tests showed that orientation change was disruptiveboth when the chromatic links were absent (p 001)and when they were present (p 002) However thesignificant interaction indicated that the presence of aconstant chromatic link attenuated the disruption effectof orientation change

EXPERIMENT 3

In Experiment 1 (and also Experiments 1Bndash1E seeTable 1) we demonstrated that selective attention to onedimension of a stimulus (location) fails to filter outchanges in another dimension (orientation) if there aremultiple elongated items This raises the question aboutwhether the influence of orientation change is completelystimulus driven or whether it can be modulated by top-down attention Studies directly addressing the relationbetween selective attention and perceptual grouping haveshown that on the one hand the spread of attention is af-fected by perceptual grouping (Egly Driver amp Rafal1994 Lavie amp Driver 1996 Vecera amp Farah 1994)whereas on the other hand top-down attention influencesperceptual grouping (Peterson amp Gibson 1994a 1994b)Because perceptual grouping by line proximity appearsto occur obligatorily it is unclear whether it can be influ-enced by selective attention In this experiment we tested

the effect of selectively attending to one group of objectsover another group and measured the disruption of loca-tion change detection produced by orientation change ofthe attended versus the ignored group Figure 4 (inset)shows an example of a display

Each display contained two sets of itemsmdashred dotswith an interposing red line segment and green dots withan interposing green line segmentmdashrandomly intermixedon a 10 10 invisible matrix The subjects were in-structed in different blocks to attend either to the reditems or to the green items and to perform location changedetection of the attended group of items To test the ef-fect of selective attention we independently varied theprobability of orientation change for the attended and theignored sets If subjects can effectively attend to the in-structed group of items and if selective attention modu-lates which items enter perceptual grouping then orien-tation changes of the attended group should have a largereffect than do orientation changes of the ignored groupHowever if the influence of orientation changes is com-pletely stimulus driven we may not observe an effect ofselective attention

MethodSubjects Seventeen observers participated in this experimentMaterials Each display contained eight red items and eight

green items randomly intermixed on a 10 10 invisible matrix(19ordm 19deg) Each item was a filled dot (04ordm 04ordm) interposed witha line segment (12ordm 12ordm) that had one of four possible orienta-tions (0ordm 45ordm 90ordm or 135ordm)

Procedure The subjects were tested in 10 practice trials and 4blocks of experimental trials containing 48 trials each Before eachblock they were instructed to attend either to the green or to the red

Figure 4 The results from Experiment 3 A sample display is shown in theinset of the figure Red (shown as black items on this figure) and green (shownas white items on this figure) items were randomly intermixed on the displayError bars indicate standard error of between-subjects variation

Neither set Distractor set Target set Both setsOrientation change

1

95

9

85

8

75

7

PERCEPTUAL GROUPING AND CHANGE DETECTION 451

items and to perform a location change detection on the filled dotsEach trial started with a 400-msec fixation point followed by amemory display (eight red items and eight green items) The mem-ory display was presented for 400 msec and then was erased Aftera blank interval of 1 sec a probe display was presented until a re-sponse was made The probe display also contained eight red andeight green items Half of the time one of the attended items changedits location to a previously blank location and half of the time theattended items maintained their locations The ignored items neverchanged locations The subjects were asked to press a right key ifthey detected a location change and a left key otherwise They weretold to ignore the oriented lines and their orientation changes Theattended items changed their orientations on 50 of the trials Fur-thermore the ignored items also changed their orientations on 50of the trials

All the factors tested in this experiment were independently ma-nipulated Thus the subjects were tested in a total of 192 experi-mental trials which can be broken down as follows 2 attended col-ors (red vs green) 2 location changes (change vs no change) 2 attended itemsrsquo orientations (change vs no change) 2 ignoreditemsrsquo orientations (change vs no change) 12 cases

ResultsWe pooled data across blocks of attending to red and

blocks of attending to green and measured A separatelyfor four conditions both attended and ignored groupsmaintained their orientations (both same) ignored groupchanged orientations (ignored different) attended groupchanged orientations (attended different) and both groupschanged orientations (both different) Figure 4 shows theresults

An ANOVA on attended group and ignored group re-vealed a signif icant main effect of attended group[F(116) 578 p 029] showing lowered A for lo-cation change detection when the attended group of itemschanged orientations The main effect of ignored groupwas not significant [F(116) 110 p 30] suggest-ing that performance was not disrupted by orientationchanges in the ignored group The interaction betweenattended group and ignored group was not significant[F(116) 241 p 14] Planned contrasts showed thatorientation change in the attended group alone was suf-ficient to disrupt performance [t (16) 247 p 05]Nonetheless orientation change in the ignored groupalone produced a marginally significant reduction in per-formance [t (16) 222 p 081] This could be causedby attention leaking to the ignored items or by a stimulus-driven effect of obligatory grouping of every item on thedisplay Thus even though this experiment did not allowus to completely rule out bottom-up effects of orientationchange on location change detection it provided clear ev-idence that such effects were significantly modulated byselective attention

EXPERIMENT 4

Two factors jointly contribute to the effect of orienta-tion change on location change detection First the spa-tial relationship among items is obligatorily encoded inthe representation of multiple locations (Jiang et al2000) Second when constructing the global configura-tion subjects are unable to extract just the pattern formed

by the dots Instead the imaginary contour formed bythe elongated objects becomes part of the global patternwhich changes when the objects rotate In Experiment 2we tried to disrupt the representation of the global pat-tern by connecting the center of the dots or by present-ing a regular grid that served as an external frame of ref-erence to represent individual dots This largely reducedthe orientation change effect

In this experiment we further eliminated the need toencode the global configuration by informing the sub-jects about which single item might change location1The informative cue serves to narrow the focus of spatialattention to a single location removing the necessity torepresent all the items and their configuration If globalshape processing is partly responsible for the disruptioneffect then no disruption from orientation is expectedwhen subjects focus on a single item

MethodSubjects Six observers were testedMaterials Each display contained eight dots that were inter-

posed by a short line segment (see Experiment 1 and Figure 1) Thefirst display was presented for 150 msec and was then erased Onesecond later another display was presented until a response wasmade The first display was presented briefly to eliminate eyemovement

Design The subjects were tested in two conditions diffuse at-tention and focal attention (Figure 5) In the diffuse attention con-dition the first display contained eight black dots and the seconddisplay contained one black dot and seven white dots The subjectswere asked to decide whether or not the black dot on the second dis-play was at one of the previous eight locations Because they had tomonitor all the dots on the first display attention was diffuse so thesubjects would have needed to encode the individual locations andtheir global configuration In the focal attention condition the firstdisplay contained one black dot and seven white dots as did the sec-ond display The subjects were asked to decide whether the blackdot on the second display was at the same location as the one on thefirst display Attention was narrow because only a single locationneeded to be extracted and monitored from the first display andthus there was no need to encode the global configuration Figure 5shows an example of the display

The subjects were tested in 20 practice trials and 160 experi-mental trials These included a factorial design of three factors ex-tent of spatial attention (diffuse vs focal) location change (samevs different) and orientation change (same vs different) An ori-entation change meant that all items rotated by 90ordm including theitem(s) that the subjects were monitoring

Results and DiscussionThe results are shown in Figure 5 We calculated Aas

well as mean response time (RT) from each subjectrsquos me-dian RT (for correct trials only) An ANOVA on atten-tion and orientation change showed that performancewas better when the subjects monitored one locationthan when they monitored eight [F(15) 3959 p 001] and when the orientation of the irrelevant line seg-ments stayed the same [F(15) 1281 p 016] Therewas also a significant interaction between set size andorientation change [F(15) 1872 p 008] suggest-ing that the effect of orientation change was modulatedby how diffuse spatial attention was Orientation changedisrupted performance only when the subjects attended

452 JIANG CHUN AND OLSON

to all locations [t (5) 434 p 007] but not when theyfocused on one location [t (5) 099 p 35]

A similar pattern of results is seen in RTs An ANOVAshowed significant effects of set size [F(15) 2693 p 003] and orientation change [F(15) 3983 p 001]and a significant interaction [F(15) 944 p 03] Ori-entation change lengthened RTs when the subjects moni-tored all locations [t(5) 776 p 001] but not whenthey focused on one location [t(5) 132 p 20]

GENERAL DISCUSSION

This study provides a compelling demonstration thatthe perceptual grouping of individual items can signifi-cantly affect change detection even when subjects areinstructed to ignore the grouping When subjects had tofocus on change detection of one dimension (the spatiallocation of elongated items) they were unable to ignorechanges in another dimension (the orientations of theitems) We believe that this is because changes in the ori-

entations of elongated objects altered their global per-ceptual organization This disruption can be reduced byan invariant frame of reference such as a regularly spacedbackground grid (Experiment 2A) by actively usingcolor feature cues to ignore the group of items that un-derwent orientation changes (Experiment 3) or by nar-rowing the focus of attention to a single item (Experi-ment 4) However the presence of constant informationwas not always sufficient (Experiment 1) and the taskdemand to ignore orientation change of the attended setof items was not always effective

The disruption of location change detection by orien-tation change is the outcome of two interrelated pro-cesses First when multiple locations need to be retainedbriefly the visual system does not simply encode each in-dividual spatial location in an egocentric or environment-based frame of reference Instead the pattern formed byall the elements is obligatorily encoded and retained Achange in the global configuration of items severely dis-rupts change detection of individual locations (Jiang

Figure 5 Sample displays and results from Experiment 4 The subjects monitored the lo-cations of the black dots Error bars indicate the standard error of the difference betweensame orientation and different orientation

Set size = 8 Diffuse Set size = 1 Focal

1

9

8

7

6

5

750

700

650

600

5501 8 1 8

Same Orientation

Different Orientation

Attended set size Attended set size

RT

(m

sec)

Same Orientation

Different Orientation

PERCEPTUAL GROUPING AND CHANGE DETECTION 453

et al 2000 Santa 1977) Configural encoding is modu-lated by attention Only items that are actively attendedbecome part of the configuration (Jiang et al 2000) Asa result changes to irrelevant locations are negligible(Experiments 3 and 4)

Perceptual grouping which is related to configural pro-cessing influences how a configuration may be formedThus manipulations that might change the perceived con-figuration can potentially disrupt the representation of lo-cations Under many conditions selective attention canoverride the potential disruption produced by irrelevantchanges For example differences in color groupingfrom memory to probe displays were negligible duringlocation change detection This suggests that perceptualgrouping by color does not influence the spatial config-uration of items The special case that cannot be disre-garded is the orientation change in the long axis of elon-gated objects even when the centers of these objectswere clearly demarcated

Configural encoding alone cannot explain the effectsof orientation change This is because the configurationformed by the dots remained the same across the two dis-plays The results can be accounted for only if the con-figuration included not just the center dots but also thelong axes Orientation change alone also fails to explainthe disruption effect because orientation change of asingle item (Experiment 4) irrelevant items (Experi-ment 3) or items encoded within an environment-basedframe of reference (Experiment 2A) did not influencechange detection of locations Such effects thereforemust arise from the interaction among elongated objectsin multi-element displays That is the relative spatial lo-cations are no longer preserved when the long axes ofthese objects are rotated

Although we did not test every kind of groupingchange that might influence change detection of loca-tions the analysis above suggests that only groupingcues that influence the relative spatial location betweenitems will have an effect Grouping cues that affect sim-ilarity without changing perceived proximity such ascolor grouping do not influence location change detec-tion On the basis of this logic the present paradigm pro-vides a tool to quantify whether certain grouping cuesinfluence the perception of spatial locations

In conclusion our study provides further support thatitems are represented in a relational manner in changedetection (Jiang et al 2000) Perceptual grouping be-tween items can affect how each item is representedeven when the grouping is task irrelevant Whether ornot grouping defined by other kinds of visual features isalso represented in change detection remains to be seen

REFERENCES

Donaldson W (1993) Accuracy of d and A as estimates of sensitiv-ity Bulletin of the Psychonomic Society 31 271-274

Egly R Driver J amp Rafal R (1994) Shifting visual attention be-tween objects and locations Evidence from normal and parietal-lesion patients Journal of Experimental Psychology General 123161-177

Grier J B (1971) Nonparametric indexes for sensitivity and biasComputing formulas Psychological Bulletin 75 424-429

Hunt S M J (1994) MacProbe A Macintosh-based experimentersworkstation for the cognitive sciences Behavior Research MethodsInstruments amp Computers 26 345-351

Jiang Y Olson I R amp Chun M M (2000) Organization of visualshort-term memory Journal of Experimental Psychology LearningMemory amp Cognition 26 683-702

Lavie N amp Driver J (1996) On the spatial extent of attention inobject-based visual selection Perception amp Psychophysics 58 1238-1251

Luck S J amp Vogel E K (1997 November) The capacity of visualworking memory for features and conjunctions Nature 390 279-281

Palmer S E (1999) Vision science Photons to phenomenologyCambridge MA MIT Press

Pashler H (1988) Familiarity and visual change detection Percep-tion amp Psychophysics 44 369-378

Peterson M A amp Gibson B S (1994a) Must shape recognition fol-low figurendashground organization An assumption in peril Psycho-logical Science 5 253-259

Peterson M A amp Gibson B S (1994b) Object recognition contri-butions to figurendashground organization Operations on outlines andsubjective contours Perception amp Psychophysics 56 551-564

Phillips W A (1974) On the distinction between sensory storage andshort-term visual memory Perception amp Psychophysics 16 283-290

Rensink R A (2002) Change detection Annual Review of Psychol-ogy 53 245-277

Rensink R A ORegan J K amp Clark J J (1997) To see or not tosee The need for attention to perceive changes in scenes Psycho-logical Science 8 368-373

Santa J L (1977) Spatial transformations of words and picturesJournal of Experimental Psychology Human Learning amp Memory3 418-427

Simons D J amp Levin D T (1997) Change blindness Trends in Cog-nitive Sciences 1 261-267

Tulving E (1974) Cue-dependent forgetting American Scientist 6274-82

Vecera S P amp Farah M J (1994) Does visual attention select ob-jects or locations Journal of Experimental Psychology General123 146-160

Woodman G F Vecera S P amp Luck S J (2003) Perceptual orga-nization influences visual working memory Psychonomic Bulletin ampReview 10 80-87

NOTE

1 We thank Robert Melara for suggesting this manipulation

(Manuscript received January 10 2003revision accepted for publication August 25 2003)

450 JIANG CHUN AND OLSON

For Experiment 2B an ANOVA revealed a significantmain effect of line orientation change [F(17) 3520p 001] a significant main effect of the presence orabsence of chromatic links [F(17) 3060 p 001]and a significant interaction between orientation changeand chromatic links [F(17) 1649 p 005] Pairwiset tests showed that orientation change was disruptiveboth when the chromatic links were absent (p 001)and when they were present (p 002) However thesignificant interaction indicated that the presence of aconstant chromatic link attenuated the disruption effectof orientation change

EXPERIMENT 3

In Experiment 1 (and also Experiments 1Bndash1E seeTable 1) we demonstrated that selective attention to onedimension of a stimulus (location) fails to filter outchanges in another dimension (orientation) if there aremultiple elongated items This raises the question aboutwhether the influence of orientation change is completelystimulus driven or whether it can be modulated by top-down attention Studies directly addressing the relationbetween selective attention and perceptual grouping haveshown that on the one hand the spread of attention is af-fected by perceptual grouping (Egly Driver amp Rafal1994 Lavie amp Driver 1996 Vecera amp Farah 1994)whereas on the other hand top-down attention influencesperceptual grouping (Peterson amp Gibson 1994a 1994b)Because perceptual grouping by line proximity appearsto occur obligatorily it is unclear whether it can be influ-enced by selective attention In this experiment we tested

the effect of selectively attending to one group of objectsover another group and measured the disruption of loca-tion change detection produced by orientation change ofthe attended versus the ignored group Figure 4 (inset)shows an example of a display

Each display contained two sets of itemsmdashred dotswith an interposing red line segment and green dots withan interposing green line segmentmdashrandomly intermixedon a 10 10 invisible matrix The subjects were in-structed in different blocks to attend either to the reditems or to the green items and to perform location changedetection of the attended group of items To test the ef-fect of selective attention we independently varied theprobability of orientation change for the attended and theignored sets If subjects can effectively attend to the in-structed group of items and if selective attention modu-lates which items enter perceptual grouping then orien-tation changes of the attended group should have a largereffect than do orientation changes of the ignored groupHowever if the influence of orientation changes is com-pletely stimulus driven we may not observe an effect ofselective attention

MethodSubjects Seventeen observers participated in this experimentMaterials Each display contained eight red items and eight

green items randomly intermixed on a 10 10 invisible matrix(19ordm 19deg) Each item was a filled dot (04ordm 04ordm) interposed witha line segment (12ordm 12ordm) that had one of four possible orienta-tions (0ordm 45ordm 90ordm or 135ordm)

Procedure The subjects were tested in 10 practice trials and 4blocks of experimental trials containing 48 trials each Before eachblock they were instructed to attend either to the green or to the red

Figure 4 The results from Experiment 3 A sample display is shown in theinset of the figure Red (shown as black items on this figure) and green (shownas white items on this figure) items were randomly intermixed on the displayError bars indicate standard error of between-subjects variation

Neither set Distractor set Target set Both setsOrientation change

1

95

9

85

8

75

7

PERCEPTUAL GROUPING AND CHANGE DETECTION 451

items and to perform a location change detection on the filled dotsEach trial started with a 400-msec fixation point followed by amemory display (eight red items and eight green items) The mem-ory display was presented for 400 msec and then was erased Aftera blank interval of 1 sec a probe display was presented until a re-sponse was made The probe display also contained eight red andeight green items Half of the time one of the attended items changedits location to a previously blank location and half of the time theattended items maintained their locations The ignored items neverchanged locations The subjects were asked to press a right key ifthey detected a location change and a left key otherwise They weretold to ignore the oriented lines and their orientation changes Theattended items changed their orientations on 50 of the trials Fur-thermore the ignored items also changed their orientations on 50of the trials

All the factors tested in this experiment were independently ma-nipulated Thus the subjects were tested in a total of 192 experi-mental trials which can be broken down as follows 2 attended col-ors (red vs green) 2 location changes (change vs no change) 2 attended itemsrsquo orientations (change vs no change) 2 ignoreditemsrsquo orientations (change vs no change) 12 cases

ResultsWe pooled data across blocks of attending to red and

blocks of attending to green and measured A separatelyfor four conditions both attended and ignored groupsmaintained their orientations (both same) ignored groupchanged orientations (ignored different) attended groupchanged orientations (attended different) and both groupschanged orientations (both different) Figure 4 shows theresults

An ANOVA on attended group and ignored group re-vealed a signif icant main effect of attended group[F(116) 578 p 029] showing lowered A for lo-cation change detection when the attended group of itemschanged orientations The main effect of ignored groupwas not significant [F(116) 110 p 30] suggest-ing that performance was not disrupted by orientationchanges in the ignored group The interaction betweenattended group and ignored group was not significant[F(116) 241 p 14] Planned contrasts showed thatorientation change in the attended group alone was suf-ficient to disrupt performance [t (16) 247 p 05]Nonetheless orientation change in the ignored groupalone produced a marginally significant reduction in per-formance [t (16) 222 p 081] This could be causedby attention leaking to the ignored items or by a stimulus-driven effect of obligatory grouping of every item on thedisplay Thus even though this experiment did not allowus to completely rule out bottom-up effects of orientationchange on location change detection it provided clear ev-idence that such effects were significantly modulated byselective attention

EXPERIMENT 4

Two factors jointly contribute to the effect of orienta-tion change on location change detection First the spa-tial relationship among items is obligatorily encoded inthe representation of multiple locations (Jiang et al2000) Second when constructing the global configura-tion subjects are unable to extract just the pattern formed

by the dots Instead the imaginary contour formed bythe elongated objects becomes part of the global patternwhich changes when the objects rotate In Experiment 2we tried to disrupt the representation of the global pat-tern by connecting the center of the dots or by present-ing a regular grid that served as an external frame of ref-erence to represent individual dots This largely reducedthe orientation change effect

In this experiment we further eliminated the need toencode the global configuration by informing the sub-jects about which single item might change location1The informative cue serves to narrow the focus of spatialattention to a single location removing the necessity torepresent all the items and their configuration If globalshape processing is partly responsible for the disruptioneffect then no disruption from orientation is expectedwhen subjects focus on a single item

MethodSubjects Six observers were testedMaterials Each display contained eight dots that were inter-

posed by a short line segment (see Experiment 1 and Figure 1) Thefirst display was presented for 150 msec and was then erased Onesecond later another display was presented until a response wasmade The first display was presented briefly to eliminate eyemovement

Design The subjects were tested in two conditions diffuse at-tention and focal attention (Figure 5) In the diffuse attention con-dition the first display contained eight black dots and the seconddisplay contained one black dot and seven white dots The subjectswere asked to decide whether or not the black dot on the second dis-play was at one of the previous eight locations Because they had tomonitor all the dots on the first display attention was diffuse so thesubjects would have needed to encode the individual locations andtheir global configuration In the focal attention condition the firstdisplay contained one black dot and seven white dots as did the sec-ond display The subjects were asked to decide whether the blackdot on the second display was at the same location as the one on thefirst display Attention was narrow because only a single locationneeded to be extracted and monitored from the first display andthus there was no need to encode the global configuration Figure 5shows an example of the display

The subjects were tested in 20 practice trials and 160 experi-mental trials These included a factorial design of three factors ex-tent of spatial attention (diffuse vs focal) location change (samevs different) and orientation change (same vs different) An ori-entation change meant that all items rotated by 90ordm including theitem(s) that the subjects were monitoring

Results and DiscussionThe results are shown in Figure 5 We calculated Aas

well as mean response time (RT) from each subjectrsquos me-dian RT (for correct trials only) An ANOVA on atten-tion and orientation change showed that performancewas better when the subjects monitored one locationthan when they monitored eight [F(15) 3959 p 001] and when the orientation of the irrelevant line seg-ments stayed the same [F(15) 1281 p 016] Therewas also a significant interaction between set size andorientation change [F(15) 1872 p 008] suggest-ing that the effect of orientation change was modulatedby how diffuse spatial attention was Orientation changedisrupted performance only when the subjects attended

452 JIANG CHUN AND OLSON

to all locations [t (5) 434 p 007] but not when theyfocused on one location [t (5) 099 p 35]

A similar pattern of results is seen in RTs An ANOVAshowed significant effects of set size [F(15) 2693 p 003] and orientation change [F(15) 3983 p 001]and a significant interaction [F(15) 944 p 03] Ori-entation change lengthened RTs when the subjects moni-tored all locations [t(5) 776 p 001] but not whenthey focused on one location [t(5) 132 p 20]

GENERAL DISCUSSION

This study provides a compelling demonstration thatthe perceptual grouping of individual items can signifi-cantly affect change detection even when subjects areinstructed to ignore the grouping When subjects had tofocus on change detection of one dimension (the spatiallocation of elongated items) they were unable to ignorechanges in another dimension (the orientations of theitems) We believe that this is because changes in the ori-

entations of elongated objects altered their global per-ceptual organization This disruption can be reduced byan invariant frame of reference such as a regularly spacedbackground grid (Experiment 2A) by actively usingcolor feature cues to ignore the group of items that un-derwent orientation changes (Experiment 3) or by nar-rowing the focus of attention to a single item (Experi-ment 4) However the presence of constant informationwas not always sufficient (Experiment 1) and the taskdemand to ignore orientation change of the attended setof items was not always effective

The disruption of location change detection by orien-tation change is the outcome of two interrelated pro-cesses First when multiple locations need to be retainedbriefly the visual system does not simply encode each in-dividual spatial location in an egocentric or environment-based frame of reference Instead the pattern formed byall the elements is obligatorily encoded and retained Achange in the global configuration of items severely dis-rupts change detection of individual locations (Jiang

Figure 5 Sample displays and results from Experiment 4 The subjects monitored the lo-cations of the black dots Error bars indicate the standard error of the difference betweensame orientation and different orientation

Set size = 8 Diffuse Set size = 1 Focal

1

9

8

7

6

5

750

700

650

600

5501 8 1 8

Same Orientation

Different Orientation

Attended set size Attended set size

RT

(m

sec)

Same Orientation

Different Orientation

PERCEPTUAL GROUPING AND CHANGE DETECTION 453

et al 2000 Santa 1977) Configural encoding is modu-lated by attention Only items that are actively attendedbecome part of the configuration (Jiang et al 2000) Asa result changes to irrelevant locations are negligible(Experiments 3 and 4)

Perceptual grouping which is related to configural pro-cessing influences how a configuration may be formedThus manipulations that might change the perceived con-figuration can potentially disrupt the representation of lo-cations Under many conditions selective attention canoverride the potential disruption produced by irrelevantchanges For example differences in color groupingfrom memory to probe displays were negligible duringlocation change detection This suggests that perceptualgrouping by color does not influence the spatial config-uration of items The special case that cannot be disre-garded is the orientation change in the long axis of elon-gated objects even when the centers of these objectswere clearly demarcated

Configural encoding alone cannot explain the effectsof orientation change This is because the configurationformed by the dots remained the same across the two dis-plays The results can be accounted for only if the con-figuration included not just the center dots but also thelong axes Orientation change alone also fails to explainthe disruption effect because orientation change of asingle item (Experiment 4) irrelevant items (Experi-ment 3) or items encoded within an environment-basedframe of reference (Experiment 2A) did not influencechange detection of locations Such effects thereforemust arise from the interaction among elongated objectsin multi-element displays That is the relative spatial lo-cations are no longer preserved when the long axes ofthese objects are rotated

Although we did not test every kind of groupingchange that might influence change detection of loca-tions the analysis above suggests that only groupingcues that influence the relative spatial location betweenitems will have an effect Grouping cues that affect sim-ilarity without changing perceived proximity such ascolor grouping do not influence location change detec-tion On the basis of this logic the present paradigm pro-vides a tool to quantify whether certain grouping cuesinfluence the perception of spatial locations

In conclusion our study provides further support thatitems are represented in a relational manner in changedetection (Jiang et al 2000) Perceptual grouping be-tween items can affect how each item is representedeven when the grouping is task irrelevant Whether ornot grouping defined by other kinds of visual features isalso represented in change detection remains to be seen

REFERENCES

Donaldson W (1993) Accuracy of d and A as estimates of sensitiv-ity Bulletin of the Psychonomic Society 31 271-274

Egly R Driver J amp Rafal R (1994) Shifting visual attention be-tween objects and locations Evidence from normal and parietal-lesion patients Journal of Experimental Psychology General 123161-177

Grier J B (1971) Nonparametric indexes for sensitivity and biasComputing formulas Psychological Bulletin 75 424-429

Hunt S M J (1994) MacProbe A Macintosh-based experimentersworkstation for the cognitive sciences Behavior Research MethodsInstruments amp Computers 26 345-351

Jiang Y Olson I R amp Chun M M (2000) Organization of visualshort-term memory Journal of Experimental Psychology LearningMemory amp Cognition 26 683-702

Lavie N amp Driver J (1996) On the spatial extent of attention inobject-based visual selection Perception amp Psychophysics 58 1238-1251

Luck S J amp Vogel E K (1997 November) The capacity of visualworking memory for features and conjunctions Nature 390 279-281

Palmer S E (1999) Vision science Photons to phenomenologyCambridge MA MIT Press

Pashler H (1988) Familiarity and visual change detection Percep-tion amp Psychophysics 44 369-378

Peterson M A amp Gibson B S (1994a) Must shape recognition fol-low figurendashground organization An assumption in peril Psycho-logical Science 5 253-259

Peterson M A amp Gibson B S (1994b) Object recognition contri-butions to figurendashground organization Operations on outlines andsubjective contours Perception amp Psychophysics 56 551-564

Phillips W A (1974) On the distinction between sensory storage andshort-term visual memory Perception amp Psychophysics 16 283-290

Rensink R A (2002) Change detection Annual Review of Psychol-ogy 53 245-277

Rensink R A ORegan J K amp Clark J J (1997) To see or not tosee The need for attention to perceive changes in scenes Psycho-logical Science 8 368-373

Santa J L (1977) Spatial transformations of words and picturesJournal of Experimental Psychology Human Learning amp Memory3 418-427

Simons D J amp Levin D T (1997) Change blindness Trends in Cog-nitive Sciences 1 261-267

Tulving E (1974) Cue-dependent forgetting American Scientist 6274-82

Vecera S P amp Farah M J (1994) Does visual attention select ob-jects or locations Journal of Experimental Psychology General123 146-160

Woodman G F Vecera S P amp Luck S J (2003) Perceptual orga-nization influences visual working memory Psychonomic Bulletin ampReview 10 80-87

NOTE

1 We thank Robert Melara for suggesting this manipulation

(Manuscript received January 10 2003revision accepted for publication August 25 2003)

PERCEPTUAL GROUPING AND CHANGE DETECTION 451

items and to perform a location change detection on the filled dotsEach trial started with a 400-msec fixation point followed by amemory display (eight red items and eight green items) The mem-ory display was presented for 400 msec and then was erased Aftera blank interval of 1 sec a probe display was presented until a re-sponse was made The probe display also contained eight red andeight green items Half of the time one of the attended items changedits location to a previously blank location and half of the time theattended items maintained their locations The ignored items neverchanged locations The subjects were asked to press a right key ifthey detected a location change and a left key otherwise They weretold to ignore the oriented lines and their orientation changes Theattended items changed their orientations on 50 of the trials Fur-thermore the ignored items also changed their orientations on 50of the trials

All the factors tested in this experiment were independently ma-nipulated Thus the subjects were tested in a total of 192 experi-mental trials which can be broken down as follows 2 attended col-ors (red vs green) 2 location changes (change vs no change) 2 attended itemsrsquo orientations (change vs no change) 2 ignoreditemsrsquo orientations (change vs no change) 12 cases

ResultsWe pooled data across blocks of attending to red and

blocks of attending to green and measured A separatelyfor four conditions both attended and ignored groupsmaintained their orientations (both same) ignored groupchanged orientations (ignored different) attended groupchanged orientations (attended different) and both groupschanged orientations (both different) Figure 4 shows theresults

An ANOVA on attended group and ignored group re-vealed a signif icant main effect of attended group[F(116) 578 p 029] showing lowered A for lo-cation change detection when the attended group of itemschanged orientations The main effect of ignored groupwas not significant [F(116) 110 p 30] suggest-ing that performance was not disrupted by orientationchanges in the ignored group The interaction betweenattended group and ignored group was not significant[F(116) 241 p 14] Planned contrasts showed thatorientation change in the attended group alone was suf-ficient to disrupt performance [t (16) 247 p 05]Nonetheless orientation change in the ignored groupalone produced a marginally significant reduction in per-formance [t (16) 222 p 081] This could be causedby attention leaking to the ignored items or by a stimulus-driven effect of obligatory grouping of every item on thedisplay Thus even though this experiment did not allowus to completely rule out bottom-up effects of orientationchange on location change detection it provided clear ev-idence that such effects were significantly modulated byselective attention

EXPERIMENT 4

Two factors jointly contribute to the effect of orienta-tion change on location change detection First the spa-tial relationship among items is obligatorily encoded inthe representation of multiple locations (Jiang et al2000) Second when constructing the global configura-tion subjects are unable to extract just the pattern formed

by the dots Instead the imaginary contour formed bythe elongated objects becomes part of the global patternwhich changes when the objects rotate In Experiment 2we tried to disrupt the representation of the global pat-tern by connecting the center of the dots or by present-ing a regular grid that served as an external frame of ref-erence to represent individual dots This largely reducedthe orientation change effect

In this experiment we further eliminated the need toencode the global configuration by informing the sub-jects about which single item might change location1The informative cue serves to narrow the focus of spatialattention to a single location removing the necessity torepresent all the items and their configuration If globalshape processing is partly responsible for the disruptioneffect then no disruption from orientation is expectedwhen subjects focus on a single item

MethodSubjects Six observers were testedMaterials Each display contained eight dots that were inter-

posed by a short line segment (see Experiment 1 and Figure 1) Thefirst display was presented for 150 msec and was then erased Onesecond later another display was presented until a response wasmade The first display was presented briefly to eliminate eyemovement

Design The subjects were tested in two conditions diffuse at-tention and focal attention (Figure 5) In the diffuse attention con-dition the first display contained eight black dots and the seconddisplay contained one black dot and seven white dots The subjectswere asked to decide whether or not the black dot on the second dis-play was at one of the previous eight locations Because they had tomonitor all the dots on the first display attention was diffuse so thesubjects would have needed to encode the individual locations andtheir global configuration In the focal attention condition the firstdisplay contained one black dot and seven white dots as did the sec-ond display The subjects were asked to decide whether the blackdot on the second display was at the same location as the one on thefirst display Attention was narrow because only a single locationneeded to be extracted and monitored from the first display andthus there was no need to encode the global configuration Figure 5shows an example of the display

The subjects were tested in 20 practice trials and 160 experi-mental trials These included a factorial design of three factors ex-tent of spatial attention (diffuse vs focal) location change (samevs different) and orientation change (same vs different) An ori-entation change meant that all items rotated by 90ordm including theitem(s) that the subjects were monitoring

Results and DiscussionThe results are shown in Figure 5 We calculated Aas

well as mean response time (RT) from each subjectrsquos me-dian RT (for correct trials only) An ANOVA on atten-tion and orientation change showed that performancewas better when the subjects monitored one locationthan when they monitored eight [F(15) 3959 p 001] and when the orientation of the irrelevant line seg-ments stayed the same [F(15) 1281 p 016] Therewas also a significant interaction between set size andorientation change [F(15) 1872 p 008] suggest-ing that the effect of orientation change was modulatedby how diffuse spatial attention was Orientation changedisrupted performance only when the subjects attended

452 JIANG CHUN AND OLSON

to all locations [t (5) 434 p 007] but not when theyfocused on one location [t (5) 099 p 35]

A similar pattern of results is seen in RTs An ANOVAshowed significant effects of set size [F(15) 2693 p 003] and orientation change [F(15) 3983 p 001]and a significant interaction [F(15) 944 p 03] Ori-entation change lengthened RTs when the subjects moni-tored all locations [t(5) 776 p 001] but not whenthey focused on one location [t(5) 132 p 20]

GENERAL DISCUSSION

This study provides a compelling demonstration thatthe perceptual grouping of individual items can signifi-cantly affect change detection even when subjects areinstructed to ignore the grouping When subjects had tofocus on change detection of one dimension (the spatiallocation of elongated items) they were unable to ignorechanges in another dimension (the orientations of theitems) We believe that this is because changes in the ori-

entations of elongated objects altered their global per-ceptual organization This disruption can be reduced byan invariant frame of reference such as a regularly spacedbackground grid (Experiment 2A) by actively usingcolor feature cues to ignore the group of items that un-derwent orientation changes (Experiment 3) or by nar-rowing the focus of attention to a single item (Experi-ment 4) However the presence of constant informationwas not always sufficient (Experiment 1) and the taskdemand to ignore orientation change of the attended setof items was not always effective

The disruption of location change detection by orien-tation change is the outcome of two interrelated pro-cesses First when multiple locations need to be retainedbriefly the visual system does not simply encode each in-dividual spatial location in an egocentric or environment-based frame of reference Instead the pattern formed byall the elements is obligatorily encoded and retained Achange in the global configuration of items severely dis-rupts change detection of individual locations (Jiang

Figure 5 Sample displays and results from Experiment 4 The subjects monitored the lo-cations of the black dots Error bars indicate the standard error of the difference betweensame orientation and different orientation

Set size = 8 Diffuse Set size = 1 Focal

1

9

8

7

6

5

750

700

650

600

5501 8 1 8

Same Orientation

Different Orientation

Attended set size Attended set size

RT

(m

sec)

Same Orientation

Different Orientation

PERCEPTUAL GROUPING AND CHANGE DETECTION 453

et al 2000 Santa 1977) Configural encoding is modu-lated by attention Only items that are actively attendedbecome part of the configuration (Jiang et al 2000) Asa result changes to irrelevant locations are negligible(Experiments 3 and 4)

Perceptual grouping which is related to configural pro-cessing influences how a configuration may be formedThus manipulations that might change the perceived con-figuration can potentially disrupt the representation of lo-cations Under many conditions selective attention canoverride the potential disruption produced by irrelevantchanges For example differences in color groupingfrom memory to probe displays were negligible duringlocation change detection This suggests that perceptualgrouping by color does not influence the spatial config-uration of items The special case that cannot be disre-garded is the orientation change in the long axis of elon-gated objects even when the centers of these objectswere clearly demarcated

Configural encoding alone cannot explain the effectsof orientation change This is because the configurationformed by the dots remained the same across the two dis-plays The results can be accounted for only if the con-figuration included not just the center dots but also thelong axes Orientation change alone also fails to explainthe disruption effect because orientation change of asingle item (Experiment 4) irrelevant items (Experi-ment 3) or items encoded within an environment-basedframe of reference (Experiment 2A) did not influencechange detection of locations Such effects thereforemust arise from the interaction among elongated objectsin multi-element displays That is the relative spatial lo-cations are no longer preserved when the long axes ofthese objects are rotated

Although we did not test every kind of groupingchange that might influence change detection of loca-tions the analysis above suggests that only groupingcues that influence the relative spatial location betweenitems will have an effect Grouping cues that affect sim-ilarity without changing perceived proximity such ascolor grouping do not influence location change detec-tion On the basis of this logic the present paradigm pro-vides a tool to quantify whether certain grouping cuesinfluence the perception of spatial locations

In conclusion our study provides further support thatitems are represented in a relational manner in changedetection (Jiang et al 2000) Perceptual grouping be-tween items can affect how each item is representedeven when the grouping is task irrelevant Whether ornot grouping defined by other kinds of visual features isalso represented in change detection remains to be seen

REFERENCES

Donaldson W (1993) Accuracy of d and A as estimates of sensitiv-ity Bulletin of the Psychonomic Society 31 271-274

Egly R Driver J amp Rafal R (1994) Shifting visual attention be-tween objects and locations Evidence from normal and parietal-lesion patients Journal of Experimental Psychology General 123161-177

Grier J B (1971) Nonparametric indexes for sensitivity and biasComputing formulas Psychological Bulletin 75 424-429

Hunt S M J (1994) MacProbe A Macintosh-based experimentersworkstation for the cognitive sciences Behavior Research MethodsInstruments amp Computers 26 345-351

Jiang Y Olson I R amp Chun M M (2000) Organization of visualshort-term memory Journal of Experimental Psychology LearningMemory amp Cognition 26 683-702

Lavie N amp Driver J (1996) On the spatial extent of attention inobject-based visual selection Perception amp Psychophysics 58 1238-1251

Luck S J amp Vogel E K (1997 November) The capacity of visualworking memory for features and conjunctions Nature 390 279-281

Palmer S E (1999) Vision science Photons to phenomenologyCambridge MA MIT Press

Pashler H (1988) Familiarity and visual change detection Percep-tion amp Psychophysics 44 369-378

Peterson M A amp Gibson B S (1994a) Must shape recognition fol-low figurendashground organization An assumption in peril Psycho-logical Science 5 253-259

Peterson M A amp Gibson B S (1994b) Object recognition contri-butions to figurendashground organization Operations on outlines andsubjective contours Perception amp Psychophysics 56 551-564

Phillips W A (1974) On the distinction between sensory storage andshort-term visual memory Perception amp Psychophysics 16 283-290

Rensink R A (2002) Change detection Annual Review of Psychol-ogy 53 245-277

Rensink R A ORegan J K amp Clark J J (1997) To see or not tosee The need for attention to perceive changes in scenes Psycho-logical Science 8 368-373

Santa J L (1977) Spatial transformations of words and picturesJournal of Experimental Psychology Human Learning amp Memory3 418-427

Simons D J amp Levin D T (1997) Change blindness Trends in Cog-nitive Sciences 1 261-267

Tulving E (1974) Cue-dependent forgetting American Scientist 6274-82

Vecera S P amp Farah M J (1994) Does visual attention select ob-jects or locations Journal of Experimental Psychology General123 146-160

Woodman G F Vecera S P amp Luck S J (2003) Perceptual orga-nization influences visual working memory Psychonomic Bulletin ampReview 10 80-87

NOTE

1 We thank Robert Melara for suggesting this manipulation

(Manuscript received January 10 2003revision accepted for publication August 25 2003)

452 JIANG CHUN AND OLSON

to all locations [t (5) 434 p 007] but not when theyfocused on one location [t (5) 099 p 35]

A similar pattern of results is seen in RTs An ANOVAshowed significant effects of set size [F(15) 2693 p 003] and orientation change [F(15) 3983 p 001]and a significant interaction [F(15) 944 p 03] Ori-entation change lengthened RTs when the subjects moni-tored all locations [t(5) 776 p 001] but not whenthey focused on one location [t(5) 132 p 20]

GENERAL DISCUSSION

This study provides a compelling demonstration thatthe perceptual grouping of individual items can signifi-cantly affect change detection even when subjects areinstructed to ignore the grouping When subjects had tofocus on change detection of one dimension (the spatiallocation of elongated items) they were unable to ignorechanges in another dimension (the orientations of theitems) We believe that this is because changes in the ori-

entations of elongated objects altered their global per-ceptual organization This disruption can be reduced byan invariant frame of reference such as a regularly spacedbackground grid (Experiment 2A) by actively usingcolor feature cues to ignore the group of items that un-derwent orientation changes (Experiment 3) or by nar-rowing the focus of attention to a single item (Experi-ment 4) However the presence of constant informationwas not always sufficient (Experiment 1) and the taskdemand to ignore orientation change of the attended setof items was not always effective

The disruption of location change detection by orien-tation change is the outcome of two interrelated pro-cesses First when multiple locations need to be retainedbriefly the visual system does not simply encode each in-dividual spatial location in an egocentric or environment-based frame of reference Instead the pattern formed byall the elements is obligatorily encoded and retained Achange in the global configuration of items severely dis-rupts change detection of individual locations (Jiang

Figure 5 Sample displays and results from Experiment 4 The subjects monitored the lo-cations of the black dots Error bars indicate the standard error of the difference betweensame orientation and different orientation

Set size = 8 Diffuse Set size = 1 Focal

1

9

8

7

6

5

750

700

650

600

5501 8 1 8

Same Orientation

Different Orientation

Attended set size Attended set size

RT

(m

sec)

Same Orientation

Different Orientation

PERCEPTUAL GROUPING AND CHANGE DETECTION 453

et al 2000 Santa 1977) Configural encoding is modu-lated by attention Only items that are actively attendedbecome part of the configuration (Jiang et al 2000) Asa result changes to irrelevant locations are negligible(Experiments 3 and 4)

Perceptual grouping which is related to configural pro-cessing influences how a configuration may be formedThus manipulations that might change the perceived con-figuration can potentially disrupt the representation of lo-cations Under many conditions selective attention canoverride the potential disruption produced by irrelevantchanges For example differences in color groupingfrom memory to probe displays were negligible duringlocation change detection This suggests that perceptualgrouping by color does not influence the spatial config-uration of items The special case that cannot be disre-garded is the orientation change in the long axis of elon-gated objects even when the centers of these objectswere clearly demarcated

Configural encoding alone cannot explain the effectsof orientation change This is because the configurationformed by the dots remained the same across the two dis-plays The results can be accounted for only if the con-figuration included not just the center dots but also thelong axes Orientation change alone also fails to explainthe disruption effect because orientation change of asingle item (Experiment 4) irrelevant items (Experi-ment 3) or items encoded within an environment-basedframe of reference (Experiment 2A) did not influencechange detection of locations Such effects thereforemust arise from the interaction among elongated objectsin multi-element displays That is the relative spatial lo-cations are no longer preserved when the long axes ofthese objects are rotated

Although we did not test every kind of groupingchange that might influence change detection of loca-tions the analysis above suggests that only groupingcues that influence the relative spatial location betweenitems will have an effect Grouping cues that affect sim-ilarity without changing perceived proximity such ascolor grouping do not influence location change detec-tion On the basis of this logic the present paradigm pro-vides a tool to quantify whether certain grouping cuesinfluence the perception of spatial locations

In conclusion our study provides further support thatitems are represented in a relational manner in changedetection (Jiang et al 2000) Perceptual grouping be-tween items can affect how each item is representedeven when the grouping is task irrelevant Whether ornot grouping defined by other kinds of visual features isalso represented in change detection remains to be seen

REFERENCES

Donaldson W (1993) Accuracy of d and A as estimates of sensitiv-ity Bulletin of the Psychonomic Society 31 271-274

Egly R Driver J amp Rafal R (1994) Shifting visual attention be-tween objects and locations Evidence from normal and parietal-lesion patients Journal of Experimental Psychology General 123161-177

Grier J B (1971) Nonparametric indexes for sensitivity and biasComputing formulas Psychological Bulletin 75 424-429

Hunt S M J (1994) MacProbe A Macintosh-based experimentersworkstation for the cognitive sciences Behavior Research MethodsInstruments amp Computers 26 345-351

Jiang Y Olson I R amp Chun M M (2000) Organization of visualshort-term memory Journal of Experimental Psychology LearningMemory amp Cognition 26 683-702

Lavie N amp Driver J (1996) On the spatial extent of attention inobject-based visual selection Perception amp Psychophysics 58 1238-1251

Luck S J amp Vogel E K (1997 November) The capacity of visualworking memory for features and conjunctions Nature 390 279-281

Palmer S E (1999) Vision science Photons to phenomenologyCambridge MA MIT Press

Pashler H (1988) Familiarity and visual change detection Percep-tion amp Psychophysics 44 369-378

Peterson M A amp Gibson B S (1994a) Must shape recognition fol-low figurendashground organization An assumption in peril Psycho-logical Science 5 253-259

Peterson M A amp Gibson B S (1994b) Object recognition contri-butions to figurendashground organization Operations on outlines andsubjective contours Perception amp Psychophysics 56 551-564

Phillips W A (1974) On the distinction between sensory storage andshort-term visual memory Perception amp Psychophysics 16 283-290

Rensink R A (2002) Change detection Annual Review of Psychol-ogy 53 245-277

Rensink R A ORegan J K amp Clark J J (1997) To see or not tosee The need for attention to perceive changes in scenes Psycho-logical Science 8 368-373

Santa J L (1977) Spatial transformations of words and picturesJournal of Experimental Psychology Human Learning amp Memory3 418-427

Simons D J amp Levin D T (1997) Change blindness Trends in Cog-nitive Sciences 1 261-267

Tulving E (1974) Cue-dependent forgetting American Scientist 6274-82

Vecera S P amp Farah M J (1994) Does visual attention select ob-jects or locations Journal of Experimental Psychology General123 146-160

Woodman G F Vecera S P amp Luck S J (2003) Perceptual orga-nization influences visual working memory Psychonomic Bulletin ampReview 10 80-87

NOTE

1 We thank Robert Melara for suggesting this manipulation

(Manuscript received January 10 2003revision accepted for publication August 25 2003)

PERCEPTUAL GROUPING AND CHANGE DETECTION 453

et al 2000 Santa 1977) Configural encoding is modu-lated by attention Only items that are actively attendedbecome part of the configuration (Jiang et al 2000) Asa result changes to irrelevant locations are negligible(Experiments 3 and 4)

Perceptual grouping which is related to configural pro-cessing influences how a configuration may be formedThus manipulations that might change the perceived con-figuration can potentially disrupt the representation of lo-cations Under many conditions selective attention canoverride the potential disruption produced by irrelevantchanges For example differences in color groupingfrom memory to probe displays were negligible duringlocation change detection This suggests that perceptualgrouping by color does not influence the spatial config-uration of items The special case that cannot be disre-garded is the orientation change in the long axis of elon-gated objects even when the centers of these objectswere clearly demarcated

Configural encoding alone cannot explain the effectsof orientation change This is because the configurationformed by the dots remained the same across the two dis-plays The results can be accounted for only if the con-figuration included not just the center dots but also thelong axes Orientation change alone also fails to explainthe disruption effect because orientation change of asingle item (Experiment 4) irrelevant items (Experi-ment 3) or items encoded within an environment-basedframe of reference (Experiment 2A) did not influencechange detection of locations Such effects thereforemust arise from the interaction among elongated objectsin multi-element displays That is the relative spatial lo-cations are no longer preserved when the long axes ofthese objects are rotated

Although we did not test every kind of groupingchange that might influence change detection of loca-tions the analysis above suggests that only groupingcues that influence the relative spatial location betweenitems will have an effect Grouping cues that affect sim-ilarity without changing perceived proximity such ascolor grouping do not influence location change detec-tion On the basis of this logic the present paradigm pro-vides a tool to quantify whether certain grouping cuesinfluence the perception of spatial locations

In conclusion our study provides further support thatitems are represented in a relational manner in changedetection (Jiang et al 2000) Perceptual grouping be-tween items can affect how each item is representedeven when the grouping is task irrelevant Whether ornot grouping defined by other kinds of visual features isalso represented in change detection remains to be seen

REFERENCES

Donaldson W (1993) Accuracy of d and A as estimates of sensitiv-ity Bulletin of the Psychonomic Society 31 271-274

Egly R Driver J amp Rafal R (1994) Shifting visual attention be-tween objects and locations Evidence from normal and parietal-lesion patients Journal of Experimental Psychology General 123161-177

Grier J B (1971) Nonparametric indexes for sensitivity and biasComputing formulas Psychological Bulletin 75 424-429

Hunt S M J (1994) MacProbe A Macintosh-based experimentersworkstation for the cognitive sciences Behavior Research MethodsInstruments amp Computers 26 345-351

Jiang Y Olson I R amp Chun M M (2000) Organization of visualshort-term memory Journal of Experimental Psychology LearningMemory amp Cognition 26 683-702

Lavie N amp Driver J (1996) On the spatial extent of attention inobject-based visual selection Perception amp Psychophysics 58 1238-1251

Luck S J amp Vogel E K (1997 November) The capacity of visualworking memory for features and conjunctions Nature 390 279-281

Palmer S E (1999) Vision science Photons to phenomenologyCambridge MA MIT Press

Pashler H (1988) Familiarity and visual change detection Percep-tion amp Psychophysics 44 369-378

Peterson M A amp Gibson B S (1994a) Must shape recognition fol-low figurendashground organization An assumption in peril Psycho-logical Science 5 253-259

Peterson M A amp Gibson B S (1994b) Object recognition contri-butions to figurendashground organization Operations on outlines andsubjective contours Perception amp Psychophysics 56 551-564

Phillips W A (1974) On the distinction between sensory storage andshort-term visual memory Perception amp Psychophysics 16 283-290

Rensink R A (2002) Change detection Annual Review of Psychol-ogy 53 245-277

Rensink R A ORegan J K amp Clark J J (1997) To see or not tosee The need for attention to perceive changes in scenes Psycho-logical Science 8 368-373

Santa J L (1977) Spatial transformations of words and picturesJournal of Experimental Psychology Human Learning amp Memory3 418-427

Simons D J amp Levin D T (1997) Change blindness Trends in Cog-nitive Sciences 1 261-267

Tulving E (1974) Cue-dependent forgetting American Scientist 6274-82

Vecera S P amp Farah M J (1994) Does visual attention select ob-jects or locations Journal of Experimental Psychology General123 146-160

Woodman G F Vecera S P amp Luck S J (2003) Perceptual orga-nization influences visual working memory Psychonomic Bulletin ampReview 10 80-87

NOTE

1 We thank Robert Melara for suggesting this manipulation

(Manuscript received January 10 2003revision accepted for publication August 25 2003)