Taking a new look at looking atnothingFernanda Ferreira, Jens Apel and John M. Henderson

School of Philosophy, Psychology, and Language Sciences, University of Edinburgh, Edinburgh, EH8 9JZ, UK

Opinion

A crucial question in cognitive science is how linguisticand visual information are integrated. Previous researchhas shown that eye movements to objects in the visualenvironment are locked to linguistic input. More surpris-ingly, listeners fixate on now-empty regions that hadpreviously been occupied by relevant objects. This ‘look-ing at nothing’ phenomenon has been linked to the claimthat the visual system constructs sparse representationsof the external world and relies on saccades and fixationsto extract information in a just-in-time manner. Ourmodel provides a different explanation: based on recentwork in visual cognition and memory, it assumes thatthe visual system creates and stores detailed internalmemory representations, and that looking at nothingfacilitates retrieval of those representations.

Looking at nothingNormally, we look at things in the surrounding environ-ment [1–4], but recent work using the eye movementmonitoring technique has demonstrated that people willalso sometimes look at nothing: that is, they will fixate ona blank location if a relevant visual stimulus had previouslyoccupied that region of space [5–8]. Our shorthand phrasefor this phenomenon will be ‘looking at nothing’. Looking atnothing is of considerable interest to researchers in psycho-linguistics, visual cognition and eye movement controlbecause it lies at the interface of these different areas ofcognitive science. Moreover, looking at nothing is likely toreveal fundamental aspects of the basic memory processesthat take place during encoding and retrieval of informationfrom multiple modalities, including speech, the environ-ment, the behaviour of conversational partners and so on.The finding that people look at nothing is also consistentwith our intuition that we tend to look at empty locationswhenwe refer to an object that used to be present there. Forexample, when we mention something someone said, wemight point to the chair in which the person previously wassitting.

Here, we discuss the looking at nothing phenomenonand use it to motivate a cognitive architecture for theintegration of visual, spatial, linguistic and conceptualinformation. One important feature of our account is thatit challenges the idea that internal representations ofthe visual world are sparse, amounting to little morethan spatial indexes for directing eye movements toobjects in the external world. This view has been invokedin past explanations of looking at nothing [5,6,8].

Corresponding author: Ferreira, F. (fernanda.edi@gmail.com).

1364-6613/$ – see front matter � 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.tics.2008.0

However, recent work in visual cognition indicates thatthe memory system actually creates quite detailed internalmemoryrepresentationsof theexternalworld [9–11], so thatinformation about objects, their specific visual propertiesand their locations are bound in a coherent memory repres-entation. In addition, because of the tight relationshipbetween encoding and retrieval [12–17], activation of anyfeature of this internal representation facilitates retrieval ofthe other features. We conclude that the reason peoplelook at nothing is that re-activation of memory representa-tions drives the eyes to previously viewed locations, andthose looks to blank regions enhance subsequent memoryretrieval.

Evidence that we look at nothingThere are now several independent demonstrations oflooking at nothing, but we focus mainly on the two ear-liest reports because they have had an important influ-ence on the way the phenomenon is currently viewed.Richardson and Spivey [6] arranged four unique faces ina 2x2 grid on a computer monitor, and each face articu-lated a different factual statement. After the fourthstatement, the faces disappeared. Participants thenheard a statement referring to one of the four facts,and their task was to say whether the statement wastrue. Eye movements were monitored throughout theexperiment. Richardson and Spivey [6] found that peopletended to look at the empty cell previously occupied bythe ‘fact-teller’ when verifying that particular fact. Torule out the possibility that participants simply linkedfaces and facts, Richardson and Spivey [6] conducted afollow-up experiment using identical spinning crossesrather than faces. These stimuli yielded essentially thesame pattern of results, indicating that the fact and thespatial information associated with the location fromwhich the fact emanated were linked. However, they alsoobserved that participants’ accuracy on the fact-verifica-tion task was no higher when participants looked at therelevant cell during fact recall, a finding that led them toargue against retrieval-based accounts of looking atnothing. Richardson and Spivey [6] argued that if lookingat nothing were a type of contextual memory effect,accuracy would have been higher when people lookedat the previously occupied location.

A similar lack of memory facilitation was found in arelated and more recent study [8]. Participants watchedwhile a computer-animated animal apparently burrowedunderground and then emerged to state a fact. The animalthen either burrowed and reappeared in a way that implied

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it was the same animal (continuity condition) or its burrow-ing behaviour implied the appearance of a second butphysically identical animal (two-animal condition). In thecontinuity condition, participants tended to fixate on boththe original and new position of the animal; but in the two-animal condition, participants ignored the second position(i.e. the second animal), presumably because it was uncon-nected to the spoken fact. In both cases, the animal was nolonger physically present, so the participants in the con-tinuity condition were actually looking at a blank screen.Theauthors [8] argued that these results providesupport forthe use of an object-based attentional mechanism thatenables the externalworld tobe consultedwhen informationmust be retrieved. In addition, like Richardson and Spivey[6], the authors [8] found no link between memory accuracyand looks to the relevant blank locations.

Altmann [5] also studied looking at nothing, but he useda rather different paradigm. His previous work withKamide and colleagues [18,19] had shown that partici-pants look at objects as they are mentioned in spokensentences. To investigate whether people look at blankregions previously occupied by relevant objects, partici-pants first saw an arrangement of four objects (e.g. aman, awoman, a cake and a newspaper) for five seconds, and thenthe entire display went blank. After one second, a spokensentence was presented (i.e. ‘the man will eat the cake’),and the trial ended five seconds later. Eyemovements weremonitored throughout. Altmann [5] observed that as thesubject of the sentence was spoken, participants looked atthe location in the blank display previously occupied bythat subject (e.g. the place where the man had been).Participants simply listened to the sentences without per-forming any extraneous task, and memory for sentencecontent was not assessed. Thus, this study does not tell usabout the relationship between looking at nothing andaccuracy of memory retrieval. What it does clearly demon-strate is a tight link between speech and eye movements toobjects no longer present but related to the content of theutterances (see Ref. [20]).

Other investigators have reported related results. Forexample, during reading, readers answering questionsabout previously read text will tend to move their eyesback to the location in the text containing the answer, evenwhen the text is no longer visible [21] (but see Ref. [22]).Johansson et al. [7] asked participants to view scenes whilelistening to a verbal description. When participants laterdescribed the scene from memory, their eye movementswere found to be similar to the pattern executed duringencoding of the scene. This tendency persisted even incomplete darkness; that is, in an environment in whichthere was no real visual information at all, so participantswere looking at nothing. Laeng and Teodorescu [23] foundthat scan patterns made by participants when they ima-gined a stimulus they had previously viewed essentiallyunder ‘blank screen’ conditions were similar to those exe-cuted during encoding of the stimulus. They also observedthat similarity in eye movement patterns from encoding toimagery predicted memory accuracy (contrary to Refs[6,8]), thus indicating that the eyemovementsmade duringthe imagery task, which is basically a blank screen, werefunctional and not just a by-product of performing the task.

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Why look at nothing? The world as its own memoryaccountAltmann [5] proposed that looking at nothing is a con-sequence of the activation of a spatial index associatedwiththe mentioned object, with a saccade automaticallylaunched to the location specified by the index [5,20]. Healso suggested that the tendency to make eye movementsto indexed locations arises because the visual system usesthe world as an external memory rather than relying oninternal representations [24,25]. Similarly to Altmann [5],Richardson and Spivey [6] proposed that viewers rely on theexternal world to serve as its own memory, rather thanbuilding and using an internal representation of the contentof the scene. In their view [5,6], the lack of internal repres-entation also explains why the oculomotor system wouldprogram a saccade to nothing: because there is no internalrepresentation of what had been present before, the visualsystem does not detect that the display has changed fromcontaining objects to being empty. Thus, people look at anempty region simply because the visual system directs eyemovements to the externalworld to get informationabout it,rather than relying on an internal, stored representation.However, this ‘world as its ownmemory’ view is inconsistentwith recent experimental evidence in visual cognition andvisual memory. Before discussing this evidence, we brieflyoutline a contrasting theory.

Why look at nothing? A representational theory of theintegration of vision and languageWe propose that looking at nothing reflects somethingimportant about the nature of mental representations.Specifically, it reflects the existence of an integrated mem-ory representation derived from visual and linguistic input[26,27]. Later, when part of an integrated representation isreactivated, the other parts are retrieved as well. This, inturn, causes the eyes to move to the location in which theitem originally appeared. Moreover, returning the eyes tothe former location of an object improves memory for all theinformation associated with that object [9,10,23], includingany concepts or propositions conveyed linguistically. In thisview, looking is both a consequence of the integrated repres-entation, and serves to facilitate retrieval of further infor-mation from it. These ideas are represented in Figure 1.

To see how thismight work, imagine that two people areembedded in a visual world such as the one shown inFigure 1c, and one of them says ‘We hailed a taxi yesterdaybut no one would stop’. The utterance and the visual worldtogether contribute to the formation of an integratedrepresentation. Some aspects of the integrated representa-tion are formed directly from the input (indicated with redlines). For example, the utterance leads to the directformation of linguistic representations (including lexicalmeaning, syntax and prosody) in addition to conceptualrepresentations (e.g. the word ‘taxi’ activates the corre-sponding concept). The visual world leads directly to theactivation of conceptual representations too, but not lin-guistic representations. Unlike the utterance, the visualworld generates visual representations (e.g. object shapes,colour, size and orientation) and leads to the creation ofspatial location indexes [28–32] which can later be used todirect eye movements to relevant objects [11].

Figure 1. Model of the integration of visual and linguistic information in memory. Part (a) represents the mental world. The clouds are for different types of representations

the cognitive system can form. Visual representations are formed from visual features; linguistic representations are formed from words and utterances; conceptual

representations are pre-stored in memory, and correspond to our knowledge of concepts and categories; and spatial location representations are formed from visual input,

and indicate the locations of objects in the visual world. Part (b) represents a spoken utterance – in this case, ‘We hailed a taxi . . ..’. Part (c) shows the visual environment in

which the interlocutors were embedded when the utterance was produced.

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The blue lines in Figure 1 indicate inter-connectionsamong internal representations. For example, an episodi-cally related conceptual representation is associated withthe corresponding visual representation (e.g. the concept‘taxicab’ is associated with information about what therelevant taxi looked like). In this way, the word ‘taxi’ mightlater activate the corresponding stored visual representa-tion of the taxi that was viewed in the same context.Figure 1 depicts all internal representations as intercon-nected. Thus, the experience of hearing the sentence ‘Wehailed a taxi. . .’ and seeing the street scene, leads to anintegrated representation containing visual, conceptual,linguistic and spatial location information. Retrieval ofany piece of this representation facilitates retrieval ofthe other pieces [12,13,17]. If the word ‘taxi’ were laterpresented, it would lead to the retrieval of informationabout the sentence, the visual properties of the image, theconcepts associated with both and the locations of theobjects. Our theory also predicts that simply moving theeyes to the location occupied previously by, say, the taxiwill activate the other information as well. As a result,looking at the empty location will facilitate memory forboth the scene and the utterance content.

Our proposal of an integrated multi-modal memoryrepresentation is related to the idea of event files [33],which is in turn related to the original idea of object files[34] (see also Refs [35–37]). Object files are integratedperceptual and conceptual representations that containan episodic trace indexed by spatio-temporal information.There is substantial evidence that retrieval from memoryis facilitated when spatio-temporal continuity or relative

location is maintained [33–37]. We extend this notion withthe proposal that during spoken language comprehension,people create a bound and integrated representation fromvisual and linguistic input, and that because of principlessuch as encoding specificity and possibly also re-enact-ment, retrieval for one part of this representation is facili-tated when another part is reinstated [12,38]. Thus, eyemovements to the appropriate region of the blank screenare made because an integrated representation wasformed during encoding, and when it is time to retrieveinformation about some part of the stimulus, retrieval ismade easier if spatial information matches. The eyes moveto where the object was both as a cause and as a con-sequence of memory retrieval.

Evidence for integrated representations:recent work in visual cognitionThe integrated representation theory assumes that peopleform detailed internal representations of the externalworld. However, this idea runs counter to the view that‘the world is its own memory’ [24,25,39,40]. The earliestdemonstrations of ‘change blindness’ were taken as evi-dence for this notion. These studies show that people canbe insensitive to large visual changes to objects right infront of their eyes [41–43]. Additional support for the ideathat the visual system relies only on spatial pointers toexternal objects but does not represent the objects them-selves [39], came from research using a block copying task[44]. People tended to look at one block to encode a relevantfeature such as colour, then look again to encode location,and so on, indicating that they did not form a memory

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representation containing information aboutmultiple fea-tures (see also Ref. [45]).

However, the notion that the cognitive system does notconstruct internal representations of the visual world hasrecently been undermined [10,11,46,47]. It is now clearthat people do, in fact, encode and retain a great deal ofinformation about the objects on which they fixate [9–11].Even more compelling are studies showing that partici-pants retain detailed information in their long-term mem-ory about objects that they are not intentionally trying toencode or remember [48,49]. People do sometimes adoptstrategies in block-copying [45,50] or scene-comparisontasks [45] that seem to involve encoding just one objector even one visual feature at a time, but this is because ofstrategic decisions to minimize working memory loadrather than an inability of the cognitive architecture toretain an internal representation [51,11].

Finally, we believe there is a serious problem with the‘world as its own memory’ account of looking at nothingwhen it involves spoken language. The problem is that theworld cannot serve as its own memory for ‘auditory’ infor-mation. That is, the ‘visual’ world can be re-sampled withfixations because objects in the environment tend to stayput. However, if you hear an utterance and thenmove youreyes to the location from which it emanated, you will notsucceed in recreating the stimulus. The eye movements,then, must be useful for reactivating an ‘internal’ repres-entation of the utterance, as our model assumes. In ourview, looking to a location will facilitate retrieval of audi-tory information from memory, and, therefore, looking atnothing might facilitate memory for spoken linguistic con-tent.

As mentioned at the beginning of this article, severalstudies show a relationship between eye movements andmemory performance. For example, Laeng and Teodorescu[23] found that similarity in scan paths from an encodingcondition to a blank-screen imagery condition predictedmemory accuracy from the encoding condition. Severalstudies in the change blindness literature have shown thatchange detection is facilitated when the eyes spon-taneously return to the changed region compared to whenthey do not [9,42]. This latter effect has also been foundwhen attention is directed to the changed region via anattentional cue [10,52]. The previously mentioned objectand event file literatures show facilitatedmemory retrievalwhen the retrieved information comes from the samelocation or the same object if its location is updated viamotion [33–37]. Thus, there is considerable evidence in theliterature that attending to and looking at a locationfacilitates retrieval of information which had occupied thatlocation.

The theory summarized in Figure 1 assumes that whenmemory is probed, spatial indexes are retrieved and theactivation of those spatial indexes increases the prob-ability of an eye movement to the corresponding spatiallocation. Recent studies show that memory for objectinformation is enhanced when an object is probed in itsoriginal spatial location. Hollingworth [52] comparedmemory for an object previously viewed within a scenewhen the object was tested in the same or in a differentscene location.He found that peopleweremore accurate at

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remembering both the specific details of the object and itsorientation when the object at test was presented in itsoriginal location in the scene. These results are consistentwith other studies, demonstrating that attending to aregion in a real-world scene facilitates retrieval of pre-viously encoded information from that region [53,54]. It,therefore, seems thatmemory for objects and their proper-ties is enhanced when spatial information at encoding,and at test, match. These findings, thus, support a funda-mental assumption of our view: integrated representa-tions including spatial indexes are naturally formedduring scene processing. In a situation in which a personlistens to speech in the context of a relevant scene, infor-mation from the utterance, the objects in the scene and thelocation of those objects are all likely to be part of suchbound memory representations. Therefore, making eyemovements to a now empty region that was previouslyoccupied by a relevant object will facilitate memory per-formance because the location information is linked toutterance and scene content.

Given our account, why did Richardson and Spivey [6]not find better memory performance for fixated emptycells? We believe their null effect was probably becauseof an item selection artefact. In the Richardson andSpivey [6] experiments, trials were sorted post hoc intofixate-on-correct-square versus fixate-on-incorrect-squarecategories. This procedure does not control for item diffi-culty across the two fixation ‘conditions’, and so it ispossible (in fact, quite likely) that facts which were moredifficult to verify triggered more saccades to the locationlinked to the fact than did facts which were easy to verify.This would lead people to make fixations to the emptyregions more often for the difficult items, and less often forthe easier ones. However, it would still be true that themore difficult items are more difficult, and so accuracymight still be lower for them. Thus, the null effect associ-ated with looking or not looking at the right empty squarecould be the result of two offsetting tendencies: looking atthe correct empty square helps performance; but thosesame items are more difficult, which depresses perform-ance. A similar explanation can account for the lack ofcorrelation between looking behaviour and memory per-formance in Hoover and Richardson [8].

Looking at nothing links the internal and externalworldsThe initial creation of a representation including spatialcodes leads to future looks when an object is re-mentioned.Looking at nothing facilitates memory retrieval for otherinformation associated with that location, including visualdetails and linguistic content. Moreover, the mechanismthat leads to facilitated memory when one looks at apreviously occupied location – namely, the existence ofan integrated representation in which multiple featuresincluding location have been encoded – also generates thelooks in the first place. In this view, when a locationcontaining an object is initially attended to and fixated,its features are bound together in an integrated trace.When some part of that trace is later cued, the restof the trace is retrieved including spatial information,which drives the eyes back to that location. An additional

Box 1. Outstanding questions

� What is the nature of spatial indexes, and to what extent does

activating them automatically versus intentionally drive the eyes

to the corresponding location?

� Are people more likely to fixate blank regions when they are trying

to retrieve information that is more difficult?

� How do our theoretical framework and the looking at nothing

phenomenon relate to reading behaviour, and in particular, the

targeting of regressive eye movements?

� What happens to people’s tendency to look at nothing when they

are immersed in dynamic environments?

� Are linguistic representations in memory affected by the co-

presence of visual information, and are visual representations in

memory affected by the co-presence of linguistic information?

� How do visual saliency and linguistic saliency map on to each

other?

� How stable are the integrated representations constructed from

visual and linguistic information? How long do they last?

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consequence of having created a bound representation isthat once the look takes place, the location then serves asan additional retrieval cue that further facilitates access ofadditional aspects of the original trace. At times, theremight even be an intentional component to this lookingbehaviour: people could learn that attending to locationsfacilitates memory retrieval, and then use that knowledgeto strategically enhance memory by re-fixating previouslyoccupied locations. However, whether the looks are inten-tional or are unconsciously triggered, the conclusion is thesame: looking at nothing is an entirely expected con-sequence of human cognitive architecture (Box 1).

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