Ecological Psychology

The term ecological has been used to characterize several theoretical positions in psychology, but only one -- that of James J. GIBSON (1966, 1979) and his successors -- is clearly relevant to cognitive science. (The others are Barker's descriptions of social behavior settings and Bronfenbrenner's analysis of the many contexts that influence the developing child; see ECOLOGICAL VALIDITY.) Gibson's views -- and their subsequent development by other theorists -- are the focus of the International Society for Ecological Psychology.The Society's journal Ecological Psychologyhas been published since 1989; the ecologically oriented International Conference on Event Perception and Actionhas met every two years since 1981.

The ecological approach rejects the cognitivist assumption of the poverty of the stimulus, that is, that perceivers must rely on MENTAL REPRESENTATIONS because they have access only to fragmentary and fallible sense-data. It also rejects many of the conventional variables that are usually regarded as the objects of perception: (absolute) distance, (absolute) size, (two-dimensional) form, etc. What people and animals actually perceive includes the layout of the environment (the arrangement of objects and surfaces, relative to one another and to the ground), the shapes of objects, the self (the perceiver's own situation in and motion through the layout), events (various types of movement and change), and especially AFFORDANCES , possibilities for effective action. These things are perceivable because they are specified by information available to appropriately tuned perceptual systems. The task of ecological psychology is to analyze that information, and to understand how animals regulate their encounters with the environment by taking advantage of it.

The ecological analysis of vision begins not with the retinal image but with the optic array. At any point of observation to which an eye might come there is already an optical structure, formed by ambient light reflected to the point from all directions. Even a static array of such points is rich in information, but the transformations generated by observer motion are richer still: they specify the layout of the environment and the perceiver's path of motion uniquely. The visual system that evolved to take advantage of this information consists of a hierarchy of active organs: a pair of movable eyes, each with its lens and chamber and retina, stabilized in their orbits by the ocular muscles and set in a mobile head on a moving body (Gibson 1966). Note that the brain does not appear in this definition: the specialized neural mechanisms essential to vision have been of relatively little interest to ecological psychologists. Vision would be impossible without the brain, but it would be equally impossible without the optic array and the mobile organs of vision.

Much of the early research in ecological psychology focused on movement-produced information, which had been largely neglected in other approaches to perception. Kinetic occlusion, for example, occurs when nearby objects hide (or reveal) others beyond them as a result of observer or object motion. In occlusion, visible elements of surface texture are systematically deleted at one side of the occluding edge but not at the other. The result is a compelling impression of relative depth as well as a perceptual form of object permanence: one sees that the occluded object is going out of sight without going out of existence (see also DEPTH PERCEPTION). Movement-produced information (including deformations of shading, highlights, etc.) also plays a significant role in the perception of object shape (Norman, Todd, and Phillips 1995).

Another form of kinetic structure is optic flow, the characteristic streaming of the array produced by observer motion. Such flows have powerful effects on posture and can create vivid illusions of self-motion. Optic flow also enables perceivers to determine their heading (i.e., the direction in which they are moving), but the details of this process are presently controversial (Cutting 1996; Warren 1995). For more on optic flow, see MID-LEVEL VISION.

Looming is the rapid magnification of a sector of the array that occurs when an object approaches the eye or the eye approaches a surface. Looming specifies impending collision, and animals of many different species -- humans, monkeys, chickens, crabs -- respond appropriately. The time remaining before collision (assuming unchanged velocity) is optically specified by a variable called tau (Lee 1980). (If X is the visual angle subtended by the approaching object or any of its parts, the tau-function is τ(X) = X/[dX / dt].) A considerable body of evidence suggests that humans and other animals use tau-related information in the control of action (e.g., Lee 1993), although the issue is not closed.

Given their focus on information structures rather than stimuli, ecological psychologists have been especially interested in amodal invariants available to more than one perceptual system. It is easy, for example, to match the shapes of seen objects with shapes felt with the hand (Gibson 1962) -- easy not just for humans but for chimpanzees (Davenport, Rogers, and Russell 1973). Runeson and Frykholm (1981) have shown that one can judge the weight of a box just as well by watching someone else lift it as by lifting it oneself, even if one's view of the lifter is just a "point-light" display. Even infants can pick up many types of tactile-visual and audiovisual invariants, matching what they see to what they hear or feel. At any age, the perceived unity of environmental events -- a person seen and heard as she walks by, the breaking of a glass that falls on the floor -- depends on our sensitivity to amodal invariants.

Ecological psychologists have been among the leaders in the study of infant perception and PERCEPTUAL DEVELOPMENT. A case in point is the discovery, cited above, that infants are sensitive to amodal invariants. Another example concerns infant locomotion: reinterpreting her classical studies of the "visual cliff," E. J. Gibson has shown that babies' willingness to venture onto a surface depends on their perception of its affordances. A sharp dropoff affords falling but not crawling; an undulating waterbed affords crawling but not walking (Gibson et al. 1987); sloping surfaces afford various modes of exploration and locomotion (Adolph, Eppler, and Gibson 1993).

J. J. Gibson's (1966) concept of a perceptual system (as opposed to a sensory modality) is particularly useful in the study of HAPTIC PERCEPTION and dynamic touch. (The older term tactile perception suggests a more passive form of experience.) The haptic system includes a rich complex of afferent and efferent nerves as well as the skin, underlying tissues, muscles, digits, and joints. This system is capable of remarkable feats: one can, for example, determine a great deal about the length, shape, and other properties of an (unseen) rigid rod simply by wielding it with one hand. Michael Turvey (1996) and his associates have shown that the rotational/mechanical invariants on which this form of perception is based can be summarized in the inertia tensor I_ij, which represents the moments of inertia specific to a given object rotated around a fixed point. Because we "wield" our own limbs in much the same sense, the inertia tensor may provide a partial basis for self-perception as well. "Simply put, moving one's limbs can be considered a case of dynamic touch" (Pagano and Turvey 1995: 1081).

Ecological psychologists have also made substantial contributions to the study of motor control. Effective action requires the coordination of many simultaneously moving body parts, each with its own inertia and other physical attributes. That coordination must be matched to the specific affordances of the immediate environment, and hence cannot be achieved by any centrally programmed pattern of impulses. This problem has been widely recognized (see MOTOR CONTROL); part of the solution may be the formation of task-specific coordinative structures. "A group of muscles spanning several different joints, and capable of contracting independently of each other, can become functionally linked so as to perform as a single task-specific unit" (Turvey 1990: 940). Turvey and his collaborators have developed this concept in a series of studies of coordinated movements.

Other perceptual systems have been studied as well: as a first step toward an ecological analysis of hearing, Gaver (1993) has recently outlined a descriptive framework for the sounds of everyday events. Fowler (1986) has advanced an ecological approach to SPEECH PERCEPTION, which can be regarded as a special case of the perception of events (specifically, the movements of the articulatory organs). Stoffregen and Riccio (1988) have proposed an ecological analysis of the vestibular system and related phenomena such as motion sickness.

Since J. J. Gibson's death in 1979, theory development in ecological psychology has taken two principal forms. On the one hand is the development of increasingly sophisticated formal descriptions of environmental structure and the information that specifies it (e.g., Bingham 1995); more generally, of animal/environment mutuality (Turvey and Shaw 1995). On the other hand are various attempts to broaden the enterprise, using ecological concepts to address a range of classical psychological issues. In this vein are Eleanor Gibson's (1994) elaboration of her theory of development, Walker-Andrews's (1997) account of the perception of emotion, my own analysis of self-perception (Neisser 1993), and the wide-ranging theoretical work of Edward Reed. Reed's book The Necessity of Experience (1996b) is a philosophical and political critique of the assumptions underlying standard cognitive science; its companion volume Encountering the World (1996a) presents ecological analyses of many topics in psychology. "Cognition," says Reed, "is neither copying nor constructing the world. Cognition is, instead, the process that keeps us active, changing creatures in touch with an eventful, changing world" (1996a: 13).

References

Adolph, K. E., M. A. Eppler, and E. J. Gibson. (1993). Crawling versus walking infants' perception of affordances for locomotion over sloping surfaces. Child Development 64:1158-1174.

Bingham, G. P. (1995). Dynamics and the problem of visual event recognition. In R. Port and T. Van Gelder, Eds., Mind as Motion: Explorations in the Dynamics of Cognition. Cambridge, MA: MIT Press.

Cutting, J. E. (1996). Wayfinding from multiple sources of local information in retinal flow. Journal of Experimental Psychology: Human Perception and Performance 22:1299-1313.

Davenport, R. K., C. M. Rogers, and I. S. Russell. (1973). Cross-modal perception in apes. Neuropsychologia 11:21-28.

Fowler, C. A. (1986). An event approach to the study of speech perception from a direct-realist perspective. Journal of Phonetics 14:3-28.

Gaver, W. W. (1993). How do we hear in the world? Explorations in ecological acoustics. Ecological Psychology 5:285-313.

Gibson, E. J. (1994). Has psychology a future? Psychological Science 5:69-76.

Gibson, E. J., G. Riccio, M. A. Schmuckler, T. A. Stoffregen, D. Rosenberg, and J. Taormina. (1987). Detection of the traversability of surfaces by crawling and walking infants. Journal of Experimental Psychology: Human Perception and Performance 13:533-544.

Gibson, J. J. (1966). The Senses Considered as Perceptual Systems. Boston: Houghton Mifflin.

Gibson, J. J. (1979). The Ecological Approach to Visual Perception. Boston: Houghton Mifflin.

Lee, D. N. (1980). The optic flow field: The foundation of vision. Philosophical Transactions of the Royal Society of London B 290:169-179.

Lee, D. N. (1993). Body-environment coupling. In U. Neisser, Ed., The Perceived Self. New York: Cambridge University Press, pp. 43-67.

Neisser, U., Ed. (1993). The Perceived Self: Ecological and Interpersonal Sources of Self-Knowledge. New York: Cambridge University Press.

Norman, J. F., J. T. Todd, and F. Phillips. (1995). The perception of surface orientation from multiple sources of information. Perception and Psychophysics 57:629-636.

Pagano, C. C., and M. T. Turvey. (1995). The inertia tensor as a basis for the perception of limb orientation. Journal of Experimental Psychology: Human Perception and Performance 21:1070-1087.

Reed, E. S. (1996a). Encountering the World: Toward an Ecological Psychology. New York: Oxford University Press.

Reed, E. S. (1996b). The Necessity of Experience. New Haven: Yale University Press.

Runeson, S., and G. Frykholm. (1981). Visual perception of lifted weight. Journal of Experimental Psychology: Human Perception and Performance 7:733-740.

Stoffregen, T. A., and G. E. Riccio. (1988). An ecological theory of orientation and the vestibular system. Psychological Review 95:3-14.

Turvey, M. T. (1990). Coordination. American Psychologist 45:938-953.

Turvey, M. T. (1996). Dynamic touch. American Psychologist 51:1134-1152.

Turvey, M. T., and R. E. Shaw. (1995). Toward an ecological physics and a physical psychology. In R. L. Solso and D. W. Massaro, Eds., The Science of the Mind: 2001 and Beyond. New York: Oxford University Press, pp. 144-169.

Walker-Andrews, A. S. (1997). Infants' perception of expressive behaviors: Differentiation of multimodal information. Psychological Bulletin 121:437-456.

Warren, W. H. (1995). Self-motion: Visual perception and visual control. In W. Epstein and S. Rogers, Eds., Perception of Space and Motion. New York: Academic Press, pp. 263-325.

Ecological Psychology

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References

Further Readings