When presented with a yellow Volkswagen and a red Ferrari, how does the brain ?gure out which color goes with which car? The binding problem refers to how the visual system

pre-consciously combines visual features of objects in the physical world to create coherent mental equivalents in our consciousness. I discuss why feature binding is a problem for our brains despite its seemingly e?ortless resolution in every-day life. Drawing from experimental cognitive psychology, I demonstrate how it manifests in space and time

Chennu, Srivas

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Kent Academic RepositoryFull text document (pdf)Copyright & reuseContent in the Kent Academic Repository is made available for research purposes. Unless otherwise stated allcontent is protected by copyright and in the absence of an open licence (eg Creative Commons), permissions for further reuse of content should be sought from the publisher, author or other copyright holder. Versions of researchThe version in the Kent Academic Repository may differ from the final published version. Users are advised to check http://kar.kent.ac.uk for the status of the paper. Users should always cite the published version of record.EnquiriesFor any further enquiries regarding the licence status of this document, please contact: researchsupport@kent.ac.ukIf you believe this document infringes copyright then please contact the KAR admin team with the take-down information provided at http://kar.kent.ac.uk/contact.htmlCitation for published versionChennu, Srivas  (2008) On Feature Binding in Space and Time.    In: University of Kent PostgraduateConference.DOILink to record in KARhttps://kar.kent.ac.uk/54658/Document VersionUNSPECIFIEDOn Feature Binding in Space and TimeSrivas ChennuPhD StudentCentre for Cognitive Neuroscience and Cognitive SystemsComputing Laboratory, University of KentCanterbury CT2 7NF, United Kingdomsrivas@gmail.comABSTRACTWhen presented with a yellow Volkswagen and a red Ferrari,how does the brain figure out which color goes with whichcar? The binding problem refers to how the visual systempre-consciously combines visual features of objects in thephysical world to create coherent mental equivalents in ourconsciousness. I discuss why feature binding is a problem forour brains despite its seemingly effortless resolution in every-day life. Drawing from experimental cognitive psychology, Idemonstrate how it manifests in space and time.KeywordsBinding Problem, Feature Binding, Temporal Binding1. INTRODUCTIONThe visual world that we are presented with everyday ismade up of a bewildering myriad of colors, shapes and sizes.Our brains are well-equipped to prevent sensory overloadand separate the ‘wheat’ from the ‘chaff’, as it were, andgive meaning to all that we perceive. But this ability islargely unconscious, seemingly instantaneous, above all re-markably efficient. The question of how such unconscious‘zombies’ in our brains collude to create an ineluctably deepconscious reality in our minds is a long-standing yet unan-swered one. Thus, fascinating though the enigmatic natureof Mona Lisa’s smile or the aesthetic beauty of a red Fer-rari may be, equally complex and mysterious are the cogni-tive mechanisms that underlie our conscious appreciation ofthose qualities.One of the prominent topics of scientific inquiry into zom-bies in the brain relates to the question of feature binding.Simply put, it is the process by which individual features ofa physical object, like color, orientation, shape, etc. mustbe correctly ‘bound together’ to create its mental represen-tation before it can be consciously perceived. That is to say,before we can ponder the beauty of either Mona Lisa or thatFerrari, the brain needs to be able to correctly put togetherPermission to make digital or hard copies of all or part of this work forpersonal or classroom use is granted without fee provided that copies arenot made or distributed for profit or commercial advantage and that copiesbear this notice and the full citation on the first page. To copy otherwise, torepublish, to post on servers or to redistribute to lists, requires prior specificpermission and/or a fee.Postgraduate Conference 2008 University of Kent, U.K.Copyright 2008 ACM X-XXXXX-XX-X/XX/XX ...$5.00.the individual parts of her face, as it must do with the linesmaking up the automobile.2. WHY IS BINDING A PROBLEM?Because of the unconscious automaticity of binding inour daily lives, we’re able to deal with the sensory over-load with apparent effortlessness. But under appropriatecircumstances, the actual processing of visual informationthat leads up to conscious perception can be experimentallystudied by inducing errors in the process, thereby demon-strating the existence of a binding problem [4]. The prob-lem itself can be boiled down to a simple question: Whenpresented with a red circle and a blue square, how does thebrain associate redness with circleness, and blueness withsquareness, and not the other way around?. This questionis rendered that much more interesting by our knowledgeof neuroanatomy elaborated on in the next section, whichtells us that information present in different brain regionsis drawn together to solve the binding problem. Hence, theproblem also serves as an illustration of how processes thatare the neural correlates of consciousness in the brain trans-late electrical activity into phenomenological experience [2].2.1 Climbing up the Visual HierarchyThe visual information processing system is architected,in some sense, as a hierarchy of processing layers. The eyesperform the initial processing of light incident on the retina,the output of which feeds up through a succession of layersin the cortex. Neurons in lower layers of the hierarchy arespecialized to respond only to specific colors and orientationsoccurring only in specific regions within our field of vision.Effectively, early visual areas are organized as spatial mapsof primitive shapes and forms, where features like color andorientation are loosely bundled together in regions in thevisual field. As activity propagates up the hierarchy, neu-rons in upper layers respond to progressively more complexshapes and objects and represent more complicated struc-tures, but at the expense of spatial detail [3].But where in this picture of the visual system does bindingcome into play? It might seem that binding is not really aproblem at all, as the spatially localized bundles of featuresin the early visual areas could be combined into coherentrepresentations in conscious perception. But as visual searchexperiments have shown, these feature bundles are not dis-tinct enough to subserve conscious experience. As we shallsee, evidence from visual search experiments demonstratesthat attention ‘glues’ together features of physical objectsinto distinct and detailed mental representations.Figure 1: Search for a differently rotated bar (left)and a red vertical bar (right). After [6].3. THE BINDING PROBLEM IN SPACEEmpirical study has demonstrated the existence of thespatial binding problem, so called because the visual systemmust correctly bind together the bundles of visual featuresat different spatial locations in our field of vision. Exper-imental tests of this phenomenon usually employ a visualsearch paradigm, where participants search for a speciallydesignated target object amongst a collection of distractingobjects displayed on a screen. Over two decades of exper-imentation have shown that we’re very good at detectingthe target if it has a single distinctive feature representedin early visual areas, like either color or orientation. Butin contrast, if the target is identifiable only by a distinctiveconjunction of such features, the task becomes a whole lotharder.The problem becomes intuitively clear in the sample searcharrays in Fig. 1. Finding an oddly oriented bar in the leftarray is almost instantaneous and effortless. This is becausethe target bar has a unique feature that makes it ‘pop out’:its orientation. The proverbial mind’s eye is automaticallydrawn to the target. On the other hand, finding a red ver-tical bar in the right array takes more work. The mind’seye must ‘rove’ the array as it is guided to the region likelyto contain the target, after which attention must bind to-gether the bundles of colors and orientations to create well-defined mental objects before one of them can be selected.We constantly use this so-called ’spotlight’ of attention toselectively filter out irrelevant details and zoom in to salientones in the world around us. Numerous experiments like thishave shown that attention acts as the binding glue that isapplied unconsciously to groups of spatial features to solvethe binding problem and subserve conscious experience [5].4. THE BINDING PROBLEM IN TIMEThe real world presents us with a dynamic and ever-changing visual environment where stimuli compete for ourattention not only in space, but also in time. As the stimuliin our field of vision change continuously, so do the corre-sponding spatial maps of their features in the brain. In otherwords, at any given point in time, the features of the stim-uli present at a given location in our visual field overlap intime with the features of stimuli presented before and af-ter it at that location. Consequently, the binding problemhas a temporal dimension to it, because in order to combinestimulus features into coherent representations in our con-scious experience, the visual system has sets of temporallyoverlapping features to pick from.This temporal variant of the binding problem shows upin experiments that employ a rapidly changing sequence ofFigure 2: A sample stream of stimuli used in a tem-poral binding experiment. Participants are requiredto identify the red letter.fleeting stimuli, presented one after the other at the samelocation on a screen. An example of such a stream of stim-uli is shown in Fig. 2, where participants must identify ared letter amongst differently colored ones. Unlike in vi-sual search, loose bundles of early visual features in theseexperiments all occur in the same location in space, and soclose to each other in time that people consciously reportthe identities of letters presented just before or after thetarget. These errors reflect incorrect bindings called Illu-sory conjunctions [1]. They are mental representations ofnon-existent physical objects, which to our conscious selvesoften seem as ‘real’ as correct bindings.The data gathered from such experiments is used to in-form our understanding of feature binding in the brain. Inaddition to recording the kind of errors participants make,we can get direct estimates of the dynamics of neuronal ac-tivity related to binding processes by recording and analyz-ing electroencephalograms (also called ‘brain waves’) fromparticipants. These electrical signals are evoked by neuronsin the brain as they process visual information, and sys-tematically reflect underlying patterns of neural activity indifferent regions of the cortex. Analysis of these patterns di-rectly inform the mechanisms by which the binding problemis solved by the brain.5. CONCLUSIONSThis paper has attempted to make a case for the existenceof a binding problem in visual perception, arguing that itsstudy gives us fascinating insights into the neural correlatesof conscious perception.6. REFERENCES[1] J. Botella, M. I. Barriopedro, and M. Suero. A model ofthe formation of illusory conjunctions in the timedomain. Journal of Experimental Psychology: HumanPerception and Performance, 27(6):1452–1467, 2001.[2] F. Crick and C. Koch. Towards a NeurobiologicalTheory of Consciousness. Seminars in theNeurosciences, 2:263–275, 1990.[3] S. Hochstein and M. Ahissar. View from the top:Hierarchies and reverse hierarchies in the visual system.Neuron, 36(5):791–804, 2002.[4] A. Treisman. The binding problem. Current Opinion inNeurobiology, 6(2):171–178, 1996.[5] J. M. Wolfe. Guided search 2.0: A revised model ofvisual search. Psychonomic Bulletin and Review,1(2):202–238, 1994.[6] J. M. Wolfe and K. R. Cave. The psychophysicalevidence for a binding problem in human vision.Neuron, 24(1):11–17, 1999.

On Feature Binding in Space and Time

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On Feature Binding in Space and Time

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