This article was downloaded by: [Queensland University of Technology]On: 22 November 2014, At: 22:17Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

ErgonomicsPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/terg20

Search for noisy coloured tracks camouflaged by noisycoloured backgroundsE. C. POULTON a & R. S. EDWARDS aa M.R.C. Applied Psychology Unit , CambridgePublished online: 27 Mar 2007.

To cite this article: E. C. POULTON & R. S. EDWARDS (1980) Search for noisy coloured tracks camouflaged by noisy colouredbackgrounds, Ergonomics, 23:3, 247-261, DOI: 10.1080/00140138008924738

To link to this article: http://dx.doi.org/10.1080/00140138008924738

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) containedin the publications on our platform. However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of theContent. Any opinions and views expressed in this publication are the opinions and views of the authors, andare not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon andshould be independently verified with primary sources of information. Taylor and Francis shall not be liable forany losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoeveror howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use ofthe Content.

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

ERGONOMICS, 1980, VOL. 23, No.3, 24'7-261

Search for noisy coloured tracks camouflaged by noisy colouredbackgrounds

By E. C. POULTON and R. S. EDWARDSM.R.C. Applied Psychology Unit, Cambridge

A total 0[67 naval ratings searched for target tracks. Four groups searched forcompJete targettracks only, while four other groups searched for both complete and faded target tracks. Thetarget tracks were lines of hexagons with a constant average slope, and ofa single colour, eitherred, yellow, green or blue. They were camouflaged by a full background matrix, comprisingabout 44% of both yellow and green hexagons, and about 6% of both red and blue hexagons,arranged randomly.

The heavily camouflaged yellow and green target tracks were detected reliably less wellthan the lightly camouflaged red and blue target tracks. The differences were particularlymarked with the faded target tracks. The interaction between camouflage and fading washighly reliable. With the heavy camouflage, searching for target tracks with a single fadeproduced a number of false detections. Whereas with light camouflage, searching for targettracks with up to three fades produced no false detection. Thus heavy camouflage isparticularly detrimental when searching for faded target tracks.

1. Introduction

1.1. Previous work 011 colour ill visual searchMuch of the early work on visual search is related to the electronic map displays

which were introduced soon after World War II. The displays show a number ofobjects, each of which can be classified in a number of ways. Thus an air traffic controldisplay may show a number of aircraft, each classified by its type, height, speed anddestination. Colour, shape, size and brightness can be used to indicate the variouscategories.

In an electronic map display, the signal at any time is the category of object beingsearched for. The noise is the remaining objects of different categories. Thus the noise iseffectively all the unwanted signals. The noise signals may resemble the wanted signalson a number of classifications which are not relevant at the particular time. Insearching for objects of a particular kind, coding by colour is the most effective form ofcoding. It is so effective that it reduces the effectiveness of independent orthogonalcodes (Christ 1975, Poulton and Edwards 1977).

However when everyone in an experiment uses a number of different conflictingcodes and tasks in turn in different experimental conditions, meaningful reliabledifferences between codes tend to disappear (Christ and Corso 1975, Teichner, Christand Corso 1977). Presumably some codes are more difficult than others, as they mustbe in similar circumstances in the real world. But the differences are concealed by thebiases introduced into the experiments by transfer from previous conditions (Poulton1975). This is less likely to happen in the real world, because each person learns toperform only a single version of the task, not conflicting alternative versions.

The present paper is concerned with a second kind of visual search task, which hasrecently increased in importance. Here the background consists largely of noise quiteunlike the signals. Only occasionally, by chance, does the background noise happen to

0014 -0139/80/23030247 SOH'll) r ' 11)1':0 T:1ylor & Francis Ltd

Dow

nloa

ded

by [

Que

ensl

and

Uni

vers

ity o

f T

echn

olog

y] a

t 22:

17 2

2 N

ovem

ber

2014

248 E. C. Poulton and R. S. Edwards

produce something like a true signal. An example from aerial reconnaisance, issearching for the remains of an aircraft which has crashed into a mountain side. Anexample from fishing by trawler, is searching for a shoal of fish in the noisy sonarreturns from the seawater.

Photographs of the earth's surface taken by a satellite may be in colour. But mostlaboratory experiments on searching in a noisy background use black and whitedisplays. The signals are often shapes or alphanumeric symbols made out of dots. Thenoise consists of extra dots.

The task used previously which is most similar to the task used here, involvessearching for a line of bright dots camouflaged by a background of bright dots. Thesignal line is found to be easier to detect when its position and slope are known, when itcontains more dots, when the dots in it are close together, and when they are spacedevenly. Detection is also easier when there are fewer noise dots in the background.However the noise dots can help detection when they happen to fall on the signal line,or on a line close to the signal line and parallel to it. Whereas when the noise dotshappen to fall on a line close to the signal line but at right angles to it, they reduce thedetecta bility of the signal (Chinnis and Uttal 1973, 1974, Lappin and Uttal 1976, Uttal,Bunnell and Corwin 1970).

1.2. Precious experiments in the present seriesThe previous experiments in the present series investigated the value of coding by

colour target tracks sloping in various directions. The tracks were all complete lines ofconstant slope. The full background matrix comprised cells of the same colours as thetarget tracks. Separate groups experimental designs were used, with a total of 168 navalratings (Poulton and Edwards 1977).

1.2.1. Searchinq for target tracks ofmore than one c%ur: At first the target tracks werered, green and blue dotted lines, with slopes ranging from ± 5° mrad to ±45° mrad.The background comprised 33% red, 33% green and 33% blue dots. A limited time of3·5 s was available for searching for a track. Sufficient practice was given over twoweeks to level off the learning curves. Searching for any of all three colours of targettrack sloping in any direction was found to be reliably less effective than searching for asingle colour of target track sloping in a single direction, either up (+ 5° to +45°) ordown (- 5° to -45°). Reducing the number of colours of target track from three to onewas found to be considerably more beneficial than reducing the number of directions ofslope from two to one. It was concluded that people can search for only one colour oftarget at a time. Whereas in this particular experiment they can search for the twodirections of slope almost as effectively as they can search for a single direction, becausethey are searching primarily by colour, not by slope.

1.2.2. Colour correlated with slope: In a second experiment, three kinds of target trackwere selected with colour and slope correlated. The red tracks sloped steeply down( - 25° to -45°) the green tracks sloped a little in either direction ( - 20° to + 20°), whilethe blue tracks sloped steeply tip (+ 25° to +45°). Searching for these three kinds oftarget track with colour and slope correlated, was found to be reliably more effectivethan searching for all three colours of target track sloping in any direction. But searchwas reliably more effective still when only onecolour of target track had to be searchedfor, sloping in any direction.

Dow

nloa

ded

by [

Que

ensl

and

Uni

vers

ity o

f T

echn

olog

y] a

t 22:

17 2

2 N

ovem

ber

2014

Search for noisy coloured tracks 249

1.2.3. Three and six colours of target track: In a third experiment three .additionalcolours of target track were added, yellow, brown and purple. The backgroundcomprised 16'5%ofeach of the six colours of dots. Searching for only the three coloursof target track, yellow, brown and purple, sloping in any direction, was found to bereliably more effective than searching for these same three colours of target track whenthey were among six colours of target track to search for. This advantage of searchingfor three colours instead of for six colours, corresponds to the advantage found earlierof searching for one colour instead of for three colours.

Searching for the red, green and blue target tracks, camouflaged by only 16'5% ofdots of each of the six colours in the background, was reliably more effective than thecorresponding condition of the first experiment with the tracks camouflaged by 33% ofred, green and blue dots in the background. The next experiment shows why the greaternumber of colours in the background is an advantage: because there are then fewer dotsof the same colour as the target track. lt isdots of the same colour which camouflage thetarget track most effectively.

1.2.4. Degrees of camoujlage by background: In the final experiment the target trackswere red, yellow, green and blue solid sloping lines of contiguous hexagons, asillustrated in Figure IA. The background comprised about 10% red, 40% yellow, 40%green and 10% blue contiguous hexagons. The solid target lines made the task a loteasier, so search time was restricted to 1·2 s. Here in the experimental condition, all fourkinds of target track had colour and slope correlated. The red tracks sloped steeplydown (-15° to _25°), the yellow tracks sloped down less steeply,(- 5° to -15°), the green tracks sloped up a little (+ 5° to + 15°)while the blue tracksloped steeply up (+ 15°to +25°). In the control conditions the target tracks were all ofa single colour, either red, yellow, green or blue, but sloped in any direction.

The effectiveness of search was found to depend upon the percentage of hexagons ofthe same colour in the background. The heavily camouflaged yellow and green targettracks were detected reliably less often when searching for all four colours of targettrack correlated with slope, than when searching for target tracks of single coloursloping in any direction. Whereas the almost uncamouflaged red and blue target trackswere always detected correctly under both conditions, because search was not required.Thus increasing the number of colours of target track to detect is a problem only whenthe tracks are camouflaged by the same colour in the background. Withoutcamouflage, tracks of four colours can be detected as effectively as tracks of a singlecolour, because search is not required.

1.3. The present experimentsAn assumption in designing the previous series of experiments is that the

background is noisy, but that the target tracks are not noisy. Yet in the real world radarand sonar signals can fade from time to time. This produces target tracks with missingcells.

In the present experiments, searching for only complete hexagon target tracks iscompared with searching for both complete and noisy or faded target tracks. A noisy orfaded target track is defined as a track containing a cell or cells of anyone of the threenon-target colours. This is a rather different use of the term fade from its conventionalusc to describe a change to a paler less saturated colour of the same kind. Using theMunsell notation described in the footnote to Table I, fading is defined as a change ofhue, not necessarily of value or chroma.

Dow

nloa

ded

by [

Que

ensl

and

Uni

vers

ity o

f T

echn

olog

y] a

t 22:

17 2

2 N

ovem

ber

2014

250 E. C. Poulton and R. S. Edwards

With the yellow and green target tracks, about 44% of the background hexagonsare the same colour as the target tracks. Allowing even a single fade produces largenumbers of chance tracks with a single fade. One display has as many as seven chancetracks with a single fade. Thus here faded target tracks are restricted to tracks with onlya single fade, and no new displays were made with faded target tracks.

In contrast, with the red and blue target tracks, only about 6% of the backgroundhexagons are the same colour as the target tracks. The only chance tracks with fades'have four or five faded hexagons out of the nine hexagons in acomplete track. Thus newdisplays were made with faded target tracks having one, two, three, four or five of thenine target hexagons replaced by hexagons of dilfereni colours.

In operational tasks, made tracks would count as targets, whether faded or not.Whereas faded tracks which occur by chancein the background would count asnontargets. However in the present experiments the man is told simply to detect anytrack with certain specifications, for example with not more than one fade. Here it doesnot matter whether the track is made deliberately, or occurs by chance in thebackground. If the man detects its, it counts as a detection.

2. Experiment I. Search for complete and slightly faded target trackswith heavy camouflage

Experiment I uses the heavily camoullaged yellow and green target tracks of theprevious experiment of section 1.2.4. It compares searching for only complete targettracks with searching for both complete target tracks and tracks with a single fade. Theresults should indicate how detectable heavily camouflaged target tracks are when theyhave a single fade, and how many false detections result from accepting as targetsheavily camouflaged tracks with a single fade.

The results should also indicate what effect, ifany, searching for faded target trackshas upon the detection of complete target tracks. The additional task of searching forfaded target tracks may distract the man from the complete target tracks. He may seewhat could be a faded target track, and spend all his search time deciding that after allthe track is not straight enough to be a target. As a result he may miss an unfaded targettrack elsewhere in the display.

On the other hand, having to report faded target tracks may increase the number ofcomplete target tracks that are reported as either complete or faded. This is becausewhen reporting only complete target tracks, the man may omit to report a complete

'track that he is doubtful about. Whereas the doubtful complete target track may be anobvious faded track. Thus it will be reported by a man having to report both completeand faded target tracks. The results should indicate which of these two possibilities isthe more important in practice.

2.1. M ethodThe method follows closely the method of the final experiment of the previous series

(Poulton and Edwards 1977).A total of 140 slides was used, each carrying an average of6'3% red, 45'3% yellow, 42·2% green and 6·2% blue hexagons. The four colours wereselected to be easily discriminable from each other. The coloured hexagons were drawnwith felt tipped pens on tracing paper. Table I specifies the colours of the pigments onthe slides, and the amount, of light that they transmit when projected onto the screen.

Dow

nloa

ded

by [

Que

ensl

and

Uni

vers

ity o

f T

echn

olog

y] a

t 22:

17 2

2 N

ovem

ber

2014

Search for noisy coloured tracks 251

Figure IA shows that the matrix of hexagons was 9 hexagons wide and 15 hexagonstall.

A complete target track was defined as a line of constant average slope, withhexagons of the same colour in everyone of the columns of the display. Figure lAshows only complete target tracks sloping up to the right. There were comparablecom plete target tracks sloping down to the right. If a hexagon of the correct colour wasabsent from one of the nine columns, or if the average slope of the line changed, it wasnot counted as a complete target track. The average slopes ranged from ± 5° to ±25°.The vertical positions and the slopes of the complete tracks were selected to cover thewhole available range.

Table I. The colours and. brightnesses of the target tracks and background

ColourNearest

Munsell notation*Transmitted light in

cd rn"?

RedYellowGreenBlue

5R 5/125Y 8/122·5G 5/8

7·5 PB 3/12

170260-2907040

*The Munsell notation gives in ~order hue or shade ofcolour, value or darknessof colour betweenwhile (10/ )andblack (0/ ), and chroma or saturation between no colour( /O)and very saturated colour ( /l2). Thus for the Red inthe top row of the Table, 5R means a middle red, 5/ meansmoderately dark, and /12 means very saturated. (MunsellColor Company Inc. 1967.).

0 B I100

~=BI~7C~~~B100

(Light 80

'"comouttoqe)

c0...

60u

'"...'"'0...C

'"u Green'-

'"Q. (Heavycornoutlcqe)

20

0 00 I

Number of fades in track---9 ~

A

Figure lA. Examplesof complete target tracks sloping upward.They have a constant average slope. Timegoes from left to right,so all the targets are travelling upward.Tracks can also slope downward. Nodisplay has more thanone made target track.The remaininghexagons in the background(not shown)are on average 6-3% red. 45-3% yellow, 42-2% green and 6-2% blue, -

Figure 18. The percentdetections of target trackswith 0 or 1 fade,when searching for both complete andfaded target tracks. Unfilled points: light camouflage, search for only 1·3s in Experiment 2. Filledpoints: heavy camouflage, search for 3-5s in Experiment I.

Dow

nloa

ded

by [

Que

ensl

and

Uni

vers

ity o

f T

echn

olog

y] a

t 22:

17 2

2 N

ovem

ber

2014

252 E. C. Poulton and R. S. Edwards

Twenty tracks were coloured yellow. Another 20 tracks with the same slopes andvertical positions were coloured green. The remaining hexagons in the matrices werethen filled at random with anyone of the four colours in the proportions previouslyindicated, using a table of random numbers (Fisher and Yates 1948). Matrices found tocontain more than one complete target track were discarded. Another 100 matriceswithout complete target tracks were also constructed from the table of randomnumbers.

The matrices were mounted in 5 x 5em slide covers. The slides were back projectedonto a translucent screen of tracing paper 8·5 x 17em by a Kodak Carousel projectorS-AVwith a l80mm lens. A hexagon then had a diameter of about I·Ocm. At thedistance of the observers a hexagon presented a visual angle of between 15 and 40minutes of arc.

Two sets of 120slides were constructed, using the 100slides without com plete targettracks, combined with either the 20 slides containing yellow complete target tracks, orthe 20 slides containing green complete target tracks. the 120 slides were arranged in afixed order in three circular slide carriers, each of which had 80 slots. An aluminiumblank separated each slide from the next. The order of the slides was determined by alimited randomization. This ensured that each slide carrier with 40 slides containedeither six or seven complete target tracks. There was also at least one complete targettrack in every quarter of the slides in each carrier.

The projected images of the slides were identical on days one and five. On days twoand six the slides were turned upside down. Target tracks previously located at the topof the display screen then appeared at the bottom, and vice versa. On days three andseven the slides were turned back to front, as well as being left upside down. Targettracks previously sloping down to the right then sloped up to the right, and.vice versa.On days four and eight the slides were left back to front, but were turned upside up as ondays one and five. This arrangement ensured that the men had seen each slide once ineach orientation on the four practice days, before they started the four test days whichsupplied their results.

On each day the order of the three slide carriers was changed according to a fixedrandom design which was the same for all conditions. The starting position within eachslide carrier was also changed in a similar way. This prevented the men from learningthe serial positions of the slides with target tracks.

2.1".1. Experimental desiqn: Columns 3 and 4 of Table 2 show that there were fourexperimental conditions, arranged in a 2 x 2 [actorial design: Both yellow and greencolours of target track were paired with searching for only complete target tracks, andwith searching for both complete target tracks and tracks with a single fade. Column 2shows that each condition was performed by a separate group of 9 to 10 men.

Faded target tracks were restricted to tracks with a single fade. The colour of thefaded hexagon could be any of the three remaining colours. On slides with completetarget tracks, allowing target tracks with a single fade put one or more faded targettracks of the same colour as the complete target track on every slide. It also put one ormore faded yellow target tracks on 68 of the 100 slides without complete target tracks.It put one or more faded green target tracks on 36 of ihe 100 slides without completetarget tracks. The slides without complete target tracks had a total of 145 faded yellowtarget tracks, but only 53 faded green target tracks. It is not clear why the differenceshould be so large. Such a large difference is unlikely to be due to the slightly greateraverage number of yellow hexagons in the background, 45'3% compared with 42'2%.

Dow

nloa

ded

by [

Que

ensl

and

Uni

vers

ity o

f T

echn

olog

y] a

t 22:

17 2

2 N

ovem

ber

2014

Search for noisy coloured tracks 253

However it provides two different ratios of complete target tracks to faded targettracks. This increases the generality of the results.

2.1.2. Procedure: The men were tested in groups of from three to six, seated in tworows one behind the other, separated by screens which prevented them from seeingeach other. The centre of the display was about 25 ern above eye level. Distances fromthe man's eyes to the display ranged from 0·8 m to 2·2 m. A light level on the responsesheets of from j·O to 5·5cd m -2 was obtained from two fluorescent strip lamps, onemounted on each side wall toward the back of the room. White noise at an intensitylevel of about 50 dB was presented by headphones, to isolate the men acoustically fromeach other during the group testing.

The 120 slides were presented each day for eight days spread over two consecutiveweeks. During the first three practice days the duration of exposure of each slide wasreduced systematically in steps, from 45 s to about 4·5 s. On the remaining five daysslides were presented automatically for about 3·5 s at intervals of 8 s. This was achievedby the aluminium blanks placed between each slide in the slide carrier of the projector.The data presented here were collected on the last four days. The tests were carried outin the early afternoon.

Each man had a stencilled response sheet. The sheet had 40 rectangles on it, each2·5 cm high x 1·25em wide, arranged in 4columns of 10.The rectangles were numberedI to 40 to correspond to the 40 slides in a slide carrier. As each slide appeared theexperimenter called out the corresponding number. The man had to draw the yellow(green) target track if he saw one, in the correct position in the rectangle and with theappropriate direction of slope. He had then to label it with the letter Y (G),corresponding to its colour, if the target track was complete. If the target trackcontained a single fade, he had to label it by the colour of the fade, R, G (Y) or B. Onlyone response was allowed per slide. For slides without target tracks, the man had towrite a large 0 in the corresponding rectangle. There was a rest period of about 5 minafter each 40 slides, during which there was conversation on neutral topics.

Scores were posted on a notice board in the men's waiting room soon after the endof each experimental period. In computing the scores for posting, each correctly locatedtarget track scored + I, while each false detection scored - 2. For the groups searchingonly for complete target tracks, the scores were expressed as a percentage of the totalpossible score, in order not to indicate the total number of possible target tracks. Justbefore the next experimental period, the posted scores of the previous day werediscussed by the experimenter and the group of men. Emphasis was placed uponavoiding false detections, as well as upon detecting as many signals as possible.

2.1.3. Scoring and statistical tests: A response was scored as correct provided it bore (I)the letter corresponding to the colour of the unfaded target track, or of the fadedhexagon if the track had a single fade, (2) sloped in the correct direction either up ordown, and (3) lay within ± 3 mm of the appropriate position of the target track withinthe rectangle. A response outside the ± 3 mm limitswas counted as a near correct,unless there was a false target track requiring the same colour response sloping in thesame direction, which was nearer to it than the true target track. In presenting theresults, corrects and near corrects have been summed.

The slides with complete target tracks all contained additional target tracks with asingle fade. In searching for both complete and faded target tracks, a faded target trackwas sometimes reported instead of the complete target track. In either case, theresponse was correct. Since only one response was allowed per slide, responding to the

Dow

nloa

ded

by [

Que

ensl

and

Uni

vers

ity o

f T

echn

olog

y] a

t 22:

17 2

2 N

ovem

ber

2014

254 E. C. Poulton wid R. S. Edwards

faded target track prevented a response to the complete target track. Thus in scoringthe responses to these slides, the correct detection of either kind of target track wascounted as a correct detection.

The measure of false detections was restricted to the slides without any targettracks, either complete or with a single fade. These slides are the same whether the manhas to report only complete target tracks, or both complete and faded tracks. Falsedetections on slides with target tracks are not scored because only one response isallowed to each slide. A correct detectiori excludes the possibility of a false detection.Thus the population of target slides on which false detections would be possible, wouldvary from person to person and from trial to trial. It would not be constant overpeopleand experimental conditions.

Nonparametric Mann- Whitney U tests and Wi/coxall tests were used (Siegel 1956).All tests were two tailed.

2.1.4. Experimental subjects: The total of 38 na val ratings had ages ranging from 16 to31 yrs, median age 19yrs. All had normal colour vision on the Ishihara test. The resultsof four additional men were excluded because they had anomalous colour vision.

2.2. Results

2.2.1. Detections Oil slides with complete tarqet tracks: The results are given in Table 2.Column 6 shows the average proportion of detections on the 80 slides with completetarget tracks presented during the four test sessions. For Groups I and 3 which have tosearch only for complete target tracks, all the detections are of complete tracks: ForGroups 2 and 4 which have to search both for complete target tracks and for trackswith a single fade, the detections can be of either kind of track.

Rows I and 2 of the table show that for the yellow target tracks, the averageproportion of slides with a detection is about the same, 91% and 92% respectively"whether or not faded target tracks have to be searched for as well as complete targettracks. This could be due to a ceiling effect. Performance is so good when having tosearch both for complete and faded target tracks, that there is little room forimprovement when only complete tracks have to be searched for.

Rows 3 and 4 show that for the green target tracks, an average of 82% of the slideshave a detection when only complete target tracks have to be searched for. Whereas an

Table 2. Results of Experiment I. Heavy camouflage, single fades, search time 3·5 s.

2 3 4 5 6 7 8 9 10 II 12Colour of Kind of Complete target tracks Target tracks with a single fade

Group N target tracks target tracks Detections False Detections Falsedetections detections

Mean Mean % Mean Mean % Mean Mean % Mean Mean %

I 9 Yellow Complete only 73 91" '0 0"2 10 Yellow Complete + 74 92b 0 0' 64 24a b 3·1 2'6d

faded3 9 Green Complete only 66 82" 1·3 0·54 10 Green Complete + 56 70' 0·3 0·1' 23 16cd 4·2 1·8'

faded

lIbcdcfg~omplete_faded p<O'002 or better

Dow

nloa

ded

by [

Que

ensl

and

Uni

vers

ity o

f T

echn

olog

y] a

t 22:

17 2

2 N

ovem

ber

2014

Search for noisy coloured tracks 255

average of only 70% of'the slides have a detection when both complete and faded trackshave to be searched for. The'difference is not quite reliable (0'05 < p< 0·1 on a 2-tailedMann-Whitney Lltest).

The advantage of searching only for complete target tracks is the reduction in theperceptual load which this entails. But the advantage has to be set against theadvantage when searching for both complete and faded target tracks of the morerelaxed criterion which can be used in reporting the complete target tracks. This isbeca use a complete target track which the man is uncertain about, can be reported as afaded track. His response is then still scored as a correct detection. Col umn 6 of Table 2shows that the two advantages more or less balance each other. Taking the yellow andgreen target tracks together, there is not a great deal of difference between the twoconditions in the proportion of detections on slides with complete target tracks.

2.2.2. Detections 011 slides with only faded target tracks: Column 10of Table 2 shows theproportion of detections on slides having only target tracks with a single fade. Theproportions average 24% for the yellow target tracks, and 16% for the green targettracks. The proportions are much smaller than the 70% to 92% of slides with completetarget tracks in Column 6, upon which a target track is detected. As the footnote to thetable indicates, the differences between the slides with complete and faded target tracksare reliable for both colours of target track (p<0·002 on Wi/coxon tests for bothGroups 2 and 4, and on Mann- Whitney U tests between Groups I and 2, and betweenGroups 3 and 4). In all four comparisons, there is no overlap between the twodistributions of percentages compared.

Throughout the experiment, legitimate target tracks with a single fade were beingreported for the first time. Some of them were previously unknown to the ex­perimenters. This reflects the difficulty of detecting some of the heavily camouflagedtracks with a single fade, which is indicated by the low average proportions ofdetections in Column 10 of the table.

However, the detections of the faded target tracks make a larger contribution to thetotal number of detections than the percentages suggest. During the four test sessions,each man sees 80 slides with complete target tracks. Column 5 of Table 2 shows that themean detections range from 74 when searching for complete and faded yellow tracks, to56 when searching for complete and faded green tracks.

Whereas during the four test sessions, each man sees 272 slides with faded yellowtarget tracks, or 144 slides with faded green target tracks. Column 9 of the table showsthat the detections average 64 faded yellow target tracks and 23 faded green targettracks. They make a useful addition to the average of74 or 56 complete target tracksdetected.

2.2.3. False detections on slides without complete or faded target tracts: Columns 8 and12 of Table 2 show the proportion of slides without any target tracks, either completeor with a single fade, upon which a target track is detected in error. Usually there is atrack, but it does not have the same average slope throughout its course. Thus it doesnot count as a target track. All the target tracks in Figure lA have a constant averageslope.

Rows I and 2 of the table show that for the yellow target tracks, the only falsedetections on slides without target tracks are of target tracks with a single fade. InGroup 2, 9 out of the 10 men incorrectly report at least one faded target track on theseslides. Whereas nobody in either Group I or Group 2 incorrectly reports a complete

Dow

nloa

ded

by [

Que

ensl

and

Uni

vers

ity o

f T

echn

olog

y] a

t 22:

17 2

2 N

ovem

ber

2014

256 E. C. Poulton and R. S. Edwards

target track on these slides. The differences between the incorrect reporting of fadedand complete target tracks are reliable (p < 0·002 in each case).

. Rows 3 and 4 of the table show that for the green target tracks, a complete targettrack is incorrectly reported on between 0·1% and 0'5% of the slides without targettracks. Whereas a faded track is incorrectly reported on 1·8% of the slides. Thedifference shown by Group 4 between the incorrectly reported complete and fadedtargets tracks is reliable (p< 0,002).

The mean numbers of false detections are given in columns 7 and II of Table 2.They range between zero and 4·2. They are quite small compared with the 'meannumbers of detections in columns 5 and 9, which range between 23 and 74. Column IIshows that most of the false detections are of target tracks with a single fade.

2.3. DiscussionThe advantage of searching for target tracks with a single fade, as well as for

complete target tracks, is the additional detections which this produces. For the yellowtarget tracks, columns 5 and 9 of Table 2 show that there are on average 73 detectionswhen searching only for complete target tracks. This can be compared with the averageof 74 +64 = 138 detections when searching for both complete and faded target tracks,an increase of 65. For the green target tracks, there are on average 66 detections whensearching only for complete target tracks, compared with the average of 56+23 = 79detections when searching for both complete.and faded target tracks, an increase of 13.

The disadvantage of searching for target tracks with a single fade, as well as forcomplete target tracks, is the additional false detections which this produces. For theyellow target tracks, columns 7 and 11 show that there are no false detections whensearching only for complete target tracks, compared with an average of 3·t falsedetections when searching for both complete and faded target tracks. For the greentarget tracks, there are on average 1·3 false detections when searching only for completetarget tracks, compared with an average of 0·3 +4·2 =4·5 false detections whensearching for both complete and faded target tracks, an increase of 3·2. In practice,whether the extra detections are worth the increase in false detections, depends uponthe' operational req uirements.

3: Experiment 2. Search for target tracks with various degrees of fading,but little camouflage

In Experiment I the yellow and green target tracks were heavily camouflaged byabout 44% of noise hexagons of the same colour in the background. Searching' fortarget tracks with a single fade, as well as for complete target tracks, cannot be donewithout increasing the proportion of false detections. In contrast, the red and bluetarget tracks are only lightly camouflaged, by about 6% of noise hexagons of the samecolour as the target hexagons. Thus here it may be possible to search without falsedetections for both complete target tracks and target tracks with a limited number offades. Experiment 2 investigates this possibility.

3.1. MethodThe method follows elosely the method of Experiment I, so only the differences will

be described. Altogether 180 slides were used. There were 20 slides with complete redtarget tracks, and 20 slides with complete blue target tracks, similar to the 20 slides withcomplete yellow and green target tracks of Experiment I. There were also the 100slides

. without complete target tracks. An additional 20 slides were drawn containing faded

Dow

nloa

ded

by [

Que

ensl

and

Uni

vers

ity o

f T

echn

olog

y] a

t 22:

17 2

2 N

ovem

ber

2014

Search Jar noisy coloured tracks 257

red target tracks. Four of the slides had tracks with only a single fade. Sets of four otherslides had tracks with 2, 3, 4 or 5 fades out of the nine hexagons comprising a targettrack. Of the faded hexagons, 10% were blue, while the remainder were half yellow andhalf green. The positions and colours of the fades were arranged according to a limitedrandomization. A similar set of 20 new slides was drawn containing faded blue targettracks. The main.difference was that 10% of the faded hexagons were red instead ofblue. ..' .

The conditions of searching for the red target tracks used the 20 slides withcomplete red tracks, the 100slides without complete target tracks, and the 40 new slidescontaining the 20 faded red and 20 faded blue target tracks. The total of 160 slides wasarranged in 4 slide carriers. The 120 basic slides were left in the same order as the slidesof Experiment 1. The 40 additional slides with fades were inserted into this series, usinga limited randomization. This ensured that every slide carrier contained five completered target tracks, and one example of each of the five degrees of faded red and bluetarget tracks. Also every quarter of the slides in each carrier had at least one faded redand one faded blue target track. For the conditions of searching for the blue targettracks, the 20 slides with complete blue target tracks were substituted for thecorresponding 20 slides with complete red target tracks.

3.1.1. Experimental design and procedure: Columns 3 and 4 of Table 3 show that therewere four conditions, similar to those of Experiment 1. Both red and blue colours oftarget track were paired with searching for only' complete target tracks, and withsearching for both complete target tracks and target tracks with up to five fades.Column 2 shows that each condition was performed by a separate group of between sixand nine men. Allowing up to five faded hexagons out of the nine in a target track, put achance red target track with five faded hexagons (in one case with only four fadedhexagons) on eight of the 100slides without complete target tracks. It put a chance bluetarget track with five faded hexagons on nine of these 100 slides.

The complete and faded target tracks were relativelyeasy to detect, because therewere few hexagons of the same colour in the background to camouflage them. Theslides were therefore presented for about 1·3s at intervals of 5·0 s. After drawing a targettrack on his response sheet, the man had to label it with the letter R (B),correspondingto its colour, if the target track was complete. A faded target track had to be labelled F.There had to be at least four hexagons of the correct colour on the course of anacceptable target track, in order to count as a faded target track.

3.1.2. Scoring: At the end of the experiment a comparison was made between thedetections of the chance target tracks with four or five fades, and of the correspondingmade target tracks with fades. Some of the chance fades were detected as often as thecorresponding made fades. But most of the chance fades were a good deal more difficultto detect. Six were never detected. Since the distributions of detections were so differentfor the chance and made fades, the results for the two kinds of faded tracks are treatedseparately.

False detections were counted only on the approximately 110 slides which did notcontain either a made target track of the correct colour with or without fades, or achance faded target track of the correct colour. Each slide giving one or more falsedetections was examined to see how many hexagons of the correct colour wereresponsible for the false detections. Usually there were only four hexagons of thecorrect colour on the false target track, but in four cases there were five hexagons. Therewere never more than five hexagons of the correct colour.

Dow

nloa

ded

by [

Que

ensl

and

Uni

vers

ity o

f T

echn

olog

y] a

t 22:

17 2

2 N

ovem

ber

2014

258 E. C. PallIcon and R. S. Edwards

3.1.3. Experimental subjects: The total of29 naval ratings had ages ranging from 17 to29 yrs, median agc 20 yrs. All had normal colour vision on the Ishihara test. The resultsof two additional men were excluded because they had anomalous colour vision.

3.2. Results

3.2.1. Dectections with light and heavy camouflage: The results are given in Table 3.Columns 6 and 7 of the table show that on average 99% or more of the complete targettracks are detected under all four conditions without any false detections. Columns 9,10and 18show that on average at least 93% of the target tracks with one and two madefades arc detected, again without any false detections. For the blue target tracks,column II shows that the number of fades has to be increased to three before theproportion of detected made faded target tracks is reliably smaller on average than thcproportion of detected complete target tracks (p< 0·01 on a Wi/coxon test). For the redtarget tracks, column 13 shows that only the proportion of detected made faded targettracks with fivc fades is reliably smaller on average than the proportion of detectedcomplete targct tracks (p < 0,01). Columns 18and 19 show that the number of fades hasto increase to four before there are any false detections.

Figure IB compares the results of Experiment 2, when searching for both completeand faded target tracks, with the corresponding results of Experiment 1. For thecomplete target tracks on the left of the figure, there are reliably more detections whenthe targct tracks are coloured red or blue, and so are hardly camouflaged, than in thecorresponding conditions when they are coloured yellow or green (p< 0·02 or better onMWlIl-Whimey U tests). For the target tracks with a single fade on the right, thedifferences between the two experiments in the proportions of detections are larger, andstill more reliable (p<O·OOI). Yet 3·5s is available for searching each slide inExperiment I, compared with only 1-3 s in Experiment 2.

In Figure IB there is a highly reliable interaction between the degree of camouflageand thc number of fades in the target tracks. For both the yellow and the green targetstracks, the distribution of the differences between one fade and no fade docs not overla pthe corresponding distribution of the differences between one fade and no fade foreither the red or the blue target tracks (p<O·OOI in each case on a Mann-lMJitney Utest). The interaction is caused by the ceiling effect with the red and blue target tracks.The red and blue target tracks with a single fade are detected so well, that there is littleroom for improved performance with the complete target tracks:

3.2.2. Detections ofchance fades and madefades: Columns 15 and 16 of Table 3 showthat there arc chance fades with four or five faded target hexagons out of the ninepossible target hexagons. The chance fades are detected on average less well than thecomparable made fades. For·the·blue target tracks with five fades, only 6% of thechance fades are detected, compared with 28% of the made fades (p<O'OI on aWi/coxon test).

In operational tasks, the chance fades do not represent true target tracks. Thusdetections of chance fades are false detections, however well the chance fades resembletrue faded target tracks. The reduced detectability of the chance fades compared to themade fades, is probably duc to the smaller total number of hexagons of the target colouron the slides. Made fades increase the number of hexagons of the target colour by thenum bcr of target hexagons of the target colour, while chance fades sim ply use the noisehexagons of the target colour already present in the background. An obvious increase

Dow

nloa

ded

by [

Que

ensl

and

Uni

vers

ity o

f T

echn

olog

y] a

t 22:

17 2

2 N

ovem

ber

2014

Tab

le3.

Res

ults

ofE

xper

imen

t2.

Lig

htca

mou

flag

e,up

to5

fade

s,se

arch

time

1'3s

.

56

78

910

11t2

1314

15t6

17t8

1920

Com

ple

teta

rget

trac

ksT

arge

ttr

acks

wit

hfa

des

Mad

efa

des

Cha

nce

fade

sF

alse

dete

ctio

nsD

etec

tion

sF

alse

Ove

rall

Ove

rall

Ove

rall

det

ecti

ons

moa

nM

ean

perc

ent

moa

nM

ean

%M

oan

Mea

npe

rcen

tG

rou

pN

Co

lou

ro

fK

ind

of

Moa

nM

ean

%w

ith

num

ber

offa

des

wit

hnu

mbe

rof

fade

sw

ith

nu

mb

er

of

fade

sta

rget

trac

ksta

rget

trac

ks1/

9-3/

9t/9

2/9

3/9

4/9

5/9

4/9-

5/9

4/9

5/9

4/9-

5/9

t/9

-3/9

4/9

5/9

Red

Com

ple

teon

ly80

too'

0R

edC

omp

lete

+fa

ded

7999

"'0

4393

'98

7976

44'

1056

27H

00-

07'

0-7'

Blu

eC

omp

lete

only

7999

'0

Blu

eC

omp

lete

+fa

ded

7999

b<df

044

96'

9682

'63

'2S

de

26'

2·2

0oo

z-O

·5h

•b

cd

Mad

efa

des

relia

bly

less

wel

ldet

ecte

dth

anco

mpl

ete

targ

ettr

acks

(p<

O·O

I)'W

ith

5fa

des,

mad

efa

des

relia

bly

bett

erde

tect

edth

anch

ance

fade

s,(p

<O

·OI)

fR

elia

bly

grea

ter

per

cent

dete

ctio

nsth

anin

the

com

para

ble

cond

itio

nof

Tab

le2

(p<

0·02

orbe

tter)

ghR

elia

bly

mor

efa

lse

dete

ctio

nsw

ith5/

9fa

des

than

with

4/9

fade

s(p

<0'

05or

bette

r)

'" '" ~ ";:;- 'Ci' .., o .~. "c ~ .., '""'- --e " "".. Or. IV V.

'0

Dow

nloa

ded

by [

Que

ensl

and

Uni

vers

ity o

f T

echn

olog

y] a

t 22:

17 2

2 N

ovem

ber

2014

260 E. C. POU/tOIl and R. S. Edwards

in the total number of hexagons on the slide. of the target colour probably alerts theman to the possible presence ofa faded target track. This presumably happens also in·operational tasks.

3.2.3. False detections offaded iarqet tracks: Columns 19 and 20 of Table 3 show thatthere arc small proportions of false detections of fades with four or five missinghexagons. False detections differ from detected fades in that the hexagons of the targetcolour are not arranged on the course of an acceptable target track. But in operationaltasks, detected chance fades and false detections are all false detections.

3.3. DiscussionTable 3 shows that with light camouflage, it is possible to search for target tracks

with up to three fades out of the nine target hexagons, without making false detections.For the red target tracks, column 5 of the table shows that there are on average 80detections when searching only for complete target tracks. Columns 5 and 8 show thatthis increases to an average of 79+43= 122 detections when searching for bothcomplete and faded target tracks, and allowing tracks with up to three fades to count astargets. For the blue target tracks, the averages are almost identical, 79 detections whensearching only for complete target tracks, and 79+44= 123 detections when searchingfor both complete and faded target tracks, and allowing tracks with up to three fades tocount as targets.

Columns 7 and 18 of Table 3 show that this is done without making any falsedetections of target tracks with three or less fades. In addition, no chance target tracksarc detected with three or less fades. The reason for these two negative results is simple.There are not sufficient red or blue hexagons in the slides without made target tracks, toproduce false or chance target tracks with as many as six red or blue hexagons, thenumber required to produce a false or chance target track with three fades. Thus it ispossible to search for target tracks with up to three fades without cost. These results arevery different fromthe results of Experiment I with the heavily camouflaged yellow andgreen target tracks.

The four colours of target track were selected to be easily discriminated from eachother. Table 1shows that the four colours have different brightnesses and saturations,as well as different hues. Clearly these differences must affect the detectability of thedifferent colours of target track. However the results for the yellow and green targettracks in Table 2 are similar. So are the results for the red and blue target tracks in Table3. This suggests that the marked differences between the results in Tables 2 and 3 aredue principally to the differences in the amount of camouflage produced by thebackground. They are not likely to be due simply to the differences between the coloursof target.

We arc grateful to Mr. Bill Hill and Mr. Mike Burke of the Admiralty Underwater WeaponsEstablishment, Procurement Executive, MoD, for presenting the problems, and for help in putting them tothe experimental test. Help was also received from Mr. Edward Elliott, Senior Psychologist (Naval). Mr.Derek Simmonds did the photography, and Dr. Ian Nimmo-Smith gave advice on the statistics. The subjectswere supplied by the Royal Navy. The work forms part of a programme of research for the Royal NavalPersonnel Research Committee.

Dow

nloa

ded

by [

Que

ensl

and

Uni

vers

ity o

f T

echn

olog

y] a

t 22:

17 2

2 N

ovem

ber

2014

Search for noisy coloured tracks 261

Soixarue-sept sujets (recrucs de la Marine) ant effectue une tache de detection de pistes-cibles, Quatregroupes ant scrute des pistes-cibles completes, alors que quatre aut res groupes cnt scrute ala fois des pistescompletes et des pistes degradees. Les pistes cibles etaient constituees d'hexagones et presentaient une pentemoyenne constante et une couleur unique, soit rouge.jaune, verte DU bleues. Elles etaient camouflees par unemat rice Ii fond plein constituee d'envieon 44%\ d'hexagones jaunes et verts et d'environ 6% d'hcxagonesrouges et bleus, disposes en structure aleatoire.

Les pistes jaunes et vertes fortement carnouflees ant ete detectees nettement mains bien que les pistesrouges et blcues legerernent camouflees. La difference etait particulierement importante avec les pistesdegradees, L'interaction entre Ie camouflage et la degradation etaieru significative. Dans lc cas ducamouflage lourd, la .r~herche des pistes presentant une lacune unique entrainait des tausses detections;alors qu'avec un camouflage legcr, on pouvait introduire jusqu'a trois degradations sans provoquer defausses detections. Par consequent. un camouflage lourd est particulierement prejudiciable ala recherche depistes-cibles degradees,

Insgcsamt 67 Marineangehorige wurden beim Zielverfolgen untersucht. Vier Gruppen suchtcn nur nachvollstandigcn Zielspuren, wahrend vier andereGruppen sowohl nach vollstandigen als auch nach schwachenZiclspuren suchten. Die Zielspuren bildeten Linien in Form von einfarbigen Sechsecken, cntweder rot. gelb,grun oder blau mit einer konstanten mittleren Veranderung. Die Zie/spuren waren durch eine volleHintergrundsmatrix (Rauschen) gelarnt, die etwa 44% sowohl der gel ben als auch der grunen Scchscckebcinhaltete, wah rend etwa 6% der roten und blauen Sechsecke beliebig zusammcngestellt waren.

Die stark vcrrauschtcn gel ben und grunen Zielspuren wurden weniger zuverlassig als die schwachverrauschten roren und blaucn geortet. Die Unterschiede waren bei den schwach verandcrten Zielspurcnbcsonders a usgepragt.

Der Zusammcnhang zwischen Rauschcn und Veranderung war sehr hoch. Bei starkem Rauschcnerbraehte die Suche nach Zielspuren mit einer einzigen Veranderung cine Reihe falschcr Ortungen, wahrendbei schwachem Rauschen die Suche nach Zielspurcn mit bis zu 3 Veranderungen keine falsche Ortungerbrachtc. Starkes Rauschen wirkt sich infolgedessen bei der Suche nach verschwornmenen Zielspurenbcsonders nachteilig a us.

ReferencesCHINNIS, J. 0., Jr., and UTTAL. W. R., 1973, Effects of random and non-random dotted visual noise on

discrimination of a dotted target line. Journal of Experimental Psychology, 100, 335-340.Cnrxxts, J. O.,Jr.. and VITAL, W. R., 1974, Tachistoscopic detectability ofdotted lines in dotted visual noise:

Signal-to-noise ratio. American Journal of Psychology, 87, 83-93.CHRIST. R. E.. 1975, Review and analysis of color coding research for visual displays. Human Factors, 17,

542-570.CIIRIST,R. E., and CORSO, G. M., 1975, Color Research for Visual Displays. Report No. ONR-CR213-102-3,

Department of Psychology, New fvfex~'o State University, Los Cruces, New Mexico 88003, U.S.A.FISHER, R. A., and YATES, F., 1948, Statistical Tablesfor Biological, Agricultural and Medical Research. 3rd

Edition. (London: OLIVER ANO BOYD).LAPPIN,J. S., and UITAI., W. R., 1976, Does prior knowledge facilitate the detection of visual targets in

random noise? Perception and Psychophysics, 20. 367-374.MUNSELL COLOR COMPANY INC., 1967, Munsell Book of Color (Baltimore, Maryland, U.S.A.).POULTON. E. C., 1975, Range effects in experiments on people. American JOIlI'/wlof Psychology, 88,3-32.POULTON, E. c., and EDWARDS, R. S., 1977, Perceptual load in searching for sloping colored lines

carnoullaged by colored backgrounds: A separate-groups investigation. Journal of ExperimentalPsycJwlogy: Human Perception ami Performance, 3.136-150.

SIEGEL, S., 1956, Nonparometric Statistics for the Behavioral Sciences. (New York: MCGRAW HILL).TEICIINER, W. H .. CIIRIST,R. E., and CORSO, G. M., 1977, Color Research for Visual Displays. Report No.

ONR-CR213-102-3-4F, Department of Psychology, Nell' Mexico State University, Las Crt/ees, NewMexico, 88003, U.S.A.

VITAL, W. R., BUNNELL, L. M.,and CORWIN,S., 1970,On thedetectability of straight lines in visual noise: Anextension of French's paradigm into the millisecond domain. Perception and Psychophysics, 8,385-388.

Manuscript received 25 September 1978.Revised manuscript received 22 October 1979.

Dow

nloa

ded

by [

Que

ensl

and

Uni

vers

ity o

f T

echn

olog

y] a

t 22:

17 2

2 N

ovem

ber

2014