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192 E Bruce Goldstein, 83 layout of surface on the terrestrialenvironment. reflectances of different areas the range of colors 1. p 87 the horizon cuts equally sized objects in the. same proportions 1 p 178 the occluding edge of,one s nose 1 p 249 size 1 p 272 the penumbra. of a shadow 1 p 286,Five of the more important invariants not. mentioned in the list above may be described as,1 Increasing density of optical texture 1 pp 67. 149 250 272 As described above texturegradients, like the one in Fig 1 remain constant as an observer. moves in relation to the gradient This constancy of. texture helps define the scale of space since equal. amounts of texture represent equal amounts of,terrain 1 p 83 and also helps determine the. perception of sizes of objects since the bases of, equally sized objects cover equal numbersof texture. 2 Flow patterns of gradients 3 p 162 1 p 182,Movement of an observer causes textures in the. environment to flow If a person is moving straight. ahead the gradient flows everywhere with the,exception of the point toward which the person is. moving which being at the center of the optical, flow pattern stays constant Thus a person s ability. to stay on course as he or she moves towards an, Fig 1 A texture gradient with two bricks object is attributed to the ability to keep the. unchanging invariant center of the optical flow,pattern centered on the desired destination. movement of an observer causes a transformationof 3 Structurecommonto two successive views 3 p. the image a regular and lawful event which leaves 261 As a person moves through the environment. certain properties of the pattern invariant For or scans it by making eye movements the views seen. example as an observer moves relative to a texture at successive points in time overlap This overlap. gradient the contours that define the textures of the helps the person to perceive a coherent continuous. gradient sweep across the retina but the texture of scene even as the scene is changing. the gradient remains constant assuming that the 4 Nondisruption of edges that are covering or. gradient is regularly spaced a point I shall returnto uncovering 1 p 76 As an observer s point of. later and the scale of depth of the scene therefore observation changes surfaces in the environment. remains constant The idea of invariant features of are seen to move relative to one another This. the environment which is introduced only briefly in movement known in the classical literature of. Ref 2 became one of the central principles of perception as motion parallax results in a pro. Gibson s approach and is discussed at length in gressive disruption of the components of surfaces. Refs 1 and 3 that are being covered the components disappear. An invariant as defined by Gibson is non from view or uncovered the components are. change that persists during change 3 p 201 and exposed to view The surface that is doing the. lawful change in the array 1 p 175 In his three covering or uncovering is defined according to. books Gibson mentions over two dozen examples Gibson by its nondisruption and this nondisruption. of invariants properties of the environment that is for Gibson an invariant. remain constant as an observer moves or when the 5 Affordances 3 p 285 1 pp 18 127 143 An. illumination changes Some of those mentioned by affordance is what the environment offers the. Gibson in his three books are Straight lines points animal what it provides orfurnishes For example. continuity 2 p 153 cues for behavior 2 p 216 a ledge affords sitting air affords breathing and. proportions 3 p 3 higher order variables of water affords drinking and bathing Thus afford. stimulus energy such as ratios of light intensity 3 p ances refer to the meanings that objects have for. 3 the Earth below the air above 3 p 8 observers and these meanings remain invariant in. rectilinearity 3 p 201 margins between patches of most situations. luminance 3 p 222 the combination of fire paired The first four invariants listed above have in. with sound warmth and odor 3 p 272 gravity 3 common a concern for the role of an active. p 319 separation of two hemispheresof light at the observer The idea that perception can be explained. horizon 1 p 76 unchanging relations among four only in terms of observers that move is a theme that. angles in a rectangle 1 p 72 a unique com runs through Gibson s work and that he has. bination of invariants a compound invariant 1 p applied not only to vision but also to other senses. The Ecology of J J Gibson s Perception 193, Thus in his paper Observations on Active Touch radically new way of thinking about perception is. 7 he analyzes touch in a new way by describing proposed 1. touch not in terms of an experimenter spush on the This statement gives an accurate picture of. skin but in terms of an observer who actively Gibson s emphasis Throughout the book he stresses. explores the surfaces of objects and he shows that the importance of movement of an observer and of. the observer s perceptions are totally different in the invariants for perception and in so doing he. two situations continues a theme begun in his other two books 2. Something common to Gibson s invariants is 3 The major new contribution is an expanded. that they are descriptions of characteristics of the discussion of affordances which were only briefly. environment or more properly descriptions of introduced in Ref 3 Thus he reaffirms his. characteristics of the stimuli for perception The commitment to invariance and direct perception. stimuli for perception are however not merely expands his discussion of affordances and sum. described in Gibson s analysis but they are given a marizes the evidence supporting these ideas I will. place of premier importance Gibson asserts not consider Gibson s treatment of affordances in. only that invariants provide the information neces variances and direct perception in turn. sary for perception but that this information exists. in a form that can be used immediately without A Affordances. being transformed processed or manipulated in Gibson s discussion of affordances focuses on. any way how information in light specifies what the environ. Gibson in fact states that space and other ment affords Thus he asks if there is information. qualities of the environment are perceived directly in light for the perception of surfaces is there. without the aid of an intervening mental process information for the perception of what they afford. For example the Helmholtzian explanation of size And he answers this question by stating that The. constancy requires that a process of unconscious values and meanings of things in the environ. inference somehow takes both retinal size and ment can be directly perceived 1 p 127 Thus. physical distance into account to achieve constancy according to him perception of an object involves. whereas Gibson s explanation requiresonly that an not only perception of the visual characteristics of. observer see how many units of a texture gradient that object but also involves perception of what the. are covered by the base of an object Thus the fact object affords And this perception of the object s. that the two bricks on the gradient of Fig 1 cover affordance like the perception of the object s visual. the same number of texture units at the point at characteristics occurs directly it is specified in the. which they rest on the ground indicates directlythat light. they are the same size and therefore eliminates Gibson correctly anticipates an objection that. according to Gibson the need for unconscious most readers would have when he states that the. inference or any other intervening mental process skeptic may not be convinced that what food. Perception is explained according to Gibson by affords something that tastes good is specified in. considering the stimuli in the environment rather light The taste of a thing the skeptic will say is. than by considering what happens to these stimuli not specified in light you can see its form or color. after they enter a person s eyes and texture but not its palatability you have to. Given the above summary of Gibson s ideas I taste it for that 1 p 140 Unfortunately he does. shall now consider the contribution made in his last not offer a way out for the skeptic Instead he says. book that affordances are specified by invariant com. binations of invariants 1 p 140 but he does not,help readers to understand exactly how these. III THE ECOLOGICALAPPROACHTO VISUAL,higher order invariants specify affordances The. PERCEPTION 1 idea that the meanings of objects are important to. In the Introduction of the book Gibson says observers is an important one a person s first. This book is a sequel to ThePerceptionof the Visual reaction to a flight of stairs may in fact be here is a. World which came out in 1950 It is ratherdifferent way to go up rather than here is a series of. however because my explanation of vision was then surfaces The problem comes with Gibson s state. based on the retinal image whereas it is now based ment that what an object affords is specified in the. on what I call the ambient optic array I now believe light and his failure to deal adequately with the fact. we must take an ecological approach to the that affordances must be learned A wooden chair. problems of perception When no constraints are may afford sitting for a human but something to. put on the visual system we look around walk up gnaw on for a beaver even though the information. to something interesting and move around it so as provided by the light is the same for both. to see it from all sides and go from one vista to Learning must occur before the information in the. another That is natural vision and that is what this light can indicate what something affords but he. book is about The process of perception is mentions learning only briefly at the end of the. not the processing of sensory inputs however but chapter when he states that affordances are. the extracting of invariants from the stimulus flux usually perceivable directly without an excessive. The old idea that sensory inputs are converted into amount of learning 1 p 143 What is missing here. perceptions by operations of the mind is rejected A is the amplification of this statement Learning. 194 E Bruce Goldstein, must be involved in a person s understanding of the sistent with the views of many other researchers. meanings of objects and this involvement deserves Many would accept the idea that it is not pictures be. more discussion than Gibson gives it they retinal neural or mental that are important in. determining perception but rather it is informa, tion some aspect of the retinal image or resulting. B Invariants neural signal that is correlated with the external en. According to Gibson invariants explain how a vironment that determines visual perceptions. person perceives the world For example the ability Thus Gibson s assertion that animals with com. to correctly perceive the sizes of objects is attributed pound eyes like the dragonfly 1 p 62 or the fiddler. to the information provided by texture gradients crab 1 p 176 can see even in the absence of a. Fig 1 and the ability to stay on course as a person retinal image poses no problem for most psycho. move towards an object is attributed to our ability logists and physiologists who require not that. to keep the unchanging invariant center of the information be in the form of a picturebut only that. optical flow pattern centered on the desired destina it be correlated with the environment. tion The idea of directperceptionhas usually however. Note that Gibson s approach has so far been been discussed not in relation to neural signals but. described without reference to any empirical re in terms of cognitive processes Gibson s claim is. search In fact it has been noted that Gibson wrote simply that perception can occur directly in a single. with a strange authority merely stating his position step based only on the information contained in the. rather than marshalling experimental evidence 8 stimulus with no intervening cognitive processing. The problem is that despite Gibson s authority and being necessary Thus direct perception changes a. the intuitive appeal of the idea of invariance some multistage process into a one stage process so that. experimental evidence must be presentedto support instead of 1 perceiving forms and 2 then. the idea that invariants are in fact used by the interpreting depth cues a person perceives the. perceptual system For example is the information layout directly in terms of invariants As Gibson. in texture gradients actually used by the perceptual puts it a person simply picks up the invariants. system to determine depth There are some studies But while he demonstrates that perception is a. on texture gradients 9 10 but few on most of the function of features on the ambient arrayof light he. other invariants fails to show that this perception is direct Thus in. This lack of experimental evidence is in fact Chapter Nine Experimental Evidence for Direct. something of which Gibson was aware In an early Perception he shows that a person s perception of. exposition of this approach he stated in 1959that it depth in a pseudotunnel 1 p 153 is dependent. has been extraordinarilyfruitful in suggesting to the on the number of intensity transitions in the tunnel. author hypotheses for experiments and in opening but it is hard to see how demonstratingthis relation. up new ways of experimentingon old problems The ship tells anything about the process that leads to. important question is whether it will serve the same the perception of depth in the tunnel. function for others 11 But 20 years later he states Perhaps the most clear cut example that Gibson. in his last book that The experiments I will cites to support direct perception is his experiment. report are mostly my own and the evidence 1 p 160 which showed that an observer can. therefore is scanty Other students of information accurately judge the heights of stakes placed on the. based perception are at work but the facts have not texture gradient formed by a plowed field The. yet been accumulated 1 p 3 The problem is that observer perceives the size of the stakes directly it is. invariants are so complex that it is difficult to know argued by noting the number of units in the texture. how to go about isolating these invariants and then gradient covered by the base of each stake thereby. studying them Recently some investigators have eliminating the need to take distance into account. taken up the challenge of investigating invariants But anyone who has walked around with a camera. 12 but this work has just begun and it remains to trying to find examples of texture gradients to. be seen whether enough empirical evidence can be photograph realizes that homogeneous texture. accumulated to support Gibson s claim that the gradients analogous to Gibson s regularly plowed. pickup of invariants can explain the totality of field are hard to find Thus in the real world one. human visual experience often encounters a nearbyobject resting on a surface. that has densely packed texture and a far away,object resting on a surface with a more widely. C Direct Perception spaced texture In this situation a person would. Gibson begins Chapter Nine of his last book 1 have to move his or her eyes from one object to the. with the statement when I assert that perception of other to see both objects clearly in foveal vision 13. the environment is direct I mean that it is not and the person would then have to carry out some. mediated by retinal pictures neural pictures or sort of mental operation to account for the change. mental pictures Direct perception is the activity of in the density between the two gradients The ability. getting information from the ambient arrayof light to make accurate judgments of size in situations. 1 p 147 such as this is difficult to explain in terms of the. If when reading this definition the word pictures direct pickup of information about the number of. is emphasized then Gibson s view is not incon texture units covered by the objects. The Ecology of J J Gibson s Perception 195, IV CONCLUSIONS Acknowledgments I thank Lynn Cooper Elizabeth Goldstein. Julian Hochberg Peter Machamer and Richard Rosinski for. What has Gibson left to us At the very their helpful comments on various drafts of the manuscript. least he has sensitized those concerned with visual. perception to the fact that to truly understand, perception they must consider the information that REFERENCES. an active observer uses while moving through the, environment But many would argue that his 1 The Ecological Approach to Visual Perception James J. contribution goes far beyond this Gibson was bold Gibson Houghton Mifflin Boston 1979 332 pp illus. enough to propose a global approach to space 2 J J Gibson The Perception of the Visual World Boston. perception at a time when most psychologists Houghton Mifflin 1950. were occupied with much narrower concerns He 3 J J Gibson The Senses Consideredas PerceptualSystems. chose to focus not on providing data but on Boston Houghton Mifflin 1966. 4 E B Goldstein Sensation and Perception Belmont CA. providing a framework to help researchers think U S A Wadsworth Publishing 1980. about perception 5 L Kaufman Perception The World Transformed New. It seems to me however that Gibson s frame York Oxford Univ Press 1979. work will not be widely accepted until others have 6 S Coren C Porac and L M Ward Sensation and. Perception New York Academic Press 1979, supplied the supporting evidence The present lack 7 J J Gibson Observations on Active Touch Psychological. of experimental support for his approach can be Rev 69 477 1962. traced at least in part to the complexity of the 8 F Restle The Seer of Ithaca Review of The Ecological. problem While it may be true that there is more to Approach to Visual Perception Contemp Psychology 25. visual perception than seeing stimuli in a labora 291 1980. 9 D Degelman and R R Rosinski Texture Gradient, tory it is another thing to be able to do meaningful Registration and the Development of Slant Perception. experiments in the complex environment that exists Child Psychology 21 339 1976. outside It may therefore be difficult to show that 10 N Levine and R R Rosinski Distance Perception under. his invariants are actually used by the visual Binocular and Monocular Viewing Conditions Perception. and Psychophysics 19 460 1976, perceptual system and even more difficult to show 11 J J Gibson Perception as a Function of Stimulation in. that perception occurs directly, Psychology A Study of a Science Vol I S Koch ed New. Whether or not some of the specifics of Gibson s York McGraw Hill 1959. approach turn out to be proveable one thing is 12 R Shaw and J Pittinger Perceiving the Face of Change in. certain He has made it necessary to think about Changing Faces Implications for a Theory of Object. Perception in Perceiving Acting and Knowing R Shaw. perception in a new way and as Ulric Neisser 14 and J Bransford eds Hillsdale N J Lawrence Erlbaum. states Gibson s insights are too far reaching and Associates 1977. too provocative to be ignored They shed an entirely 13 J Hochberg Sensation and Perception in The First. new light on the problems of perception it is Century of Experimental Psychology Eliot Hearst ed. structured light rich in information By offering us a Hillsdale N J Lawrence Erlbaum Associates 1979. 14 U Neisser Gibson s Ecological Optics Consequences of a. new description of the stimulus for vision he has Different Stimulus Description Paper presented at the. presented us with a new vision of theoretical Society for Philosophy and Psychology Ithaca NY 4 April.
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