Nägemis taju, Gibson VS Gregory (0)

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Compare and contrast the ` direct ` perception theory of Gibson with the `constructivist` perception theory of Gregory . Which provides a better account of human perception?
Sensation involves physical stimulation of the sense organs, while perception is the organisation and interpretation of incoming sensory information. The Gestalt theorists first identified many of the principles that dominate in human visual perception. As Dowell (1995) has observed : “To perceive seems effortless. To understand perception is nevertheless a great challenge ” (cited in Gross, 2005, pp 244). This essay will look at Gregory’s theory and Gibson’s theory of visual perception whether one or the other offers a better explanation of human visual perception.
According to top-down perceptual processing theorists, perception is the end result of an indirect process that involves making inferences about the world based on knowledge and expectations . An example of this process is Gregory’s (1980) constructivist theory. He suggests that to avoid sensory overload , we need to select from the information surrounding us, therefore , we often supplement perception with unconscious inferences.
Thus he argues that perception begins with an incomplete retinal image that is two-dimensional, flat and size depends on distance . He says that perception is a constructive process in which the two-dimensional retinal image is elaborated to a three- dimensional picture in our brain , based on personal knowledge and experience . In other words the processes of perception is essentially affected by our expectations and probability in perceiving the world. Therefore conceptually driven perceptual processing is called a top-down process due to the indirect process that involves making assumptions about the world.
However , another theory of visual perception is called bottom -up/data driven processes Gibson (1979). As the major bottom-up theorist, he argues that perception is a direct process, determined by the information presented to the sensory receptors. In other words, perceptions starts with light reflected by objects which creates an optic array containing all the visual information from the environment to the eye as a stationary perceiver. Although motion changes some aspects in optic array, however, it provides unambiguous and invariant information about the layout and objects in space. He differs in this information in three forms : optic flow patterns (motion and stereopsis), texture gradient and affordances.
Optic flow patterns generally refer to the changes in optic array as the perceiver moves about. Texture gradients (or gradients of texture density) are important depth cues perceived directly without the need for any inferences, as this high- order pattern or structure acts as a source of information about our environment.
Affordances are directly perceivable potential uses or objects, and are closely linked with ecological optics. When an object moves further away from the eye, its image gets smaller (relative size); most objects are bounded by texture surfaces and texture gradient gets finer as an object recedes. Bruce & Green (1990) argue that Gibson’s concept of affordances is most powerful and useful in the context of visually guided behaviour, as observed in insects. For example, objects aren ’t judged in complete isolation, and the optic array commonly contains far more information than is associated with a single stimulus.
The ability to perceive the object as unchanging, despite changes in the sensory information (size, shape, colour , brightness or location ) that reaches the eye is called perceptual constancy. And perceptual constancies tell us that visual information from the retinal image is sketchy and incomplete, and that the visual information has to travel beyond the retinal image in order to be more complete.
For this reason , Gregory argues that perception must be an indirect process involving a construction based on physical sources of energy. From this point of view there is a footing for explanation of illusions in which some of them he has explained successfully. Gregory argues that when we experience a visual illusion what we perceive may not be physically present in the retinal image. Illusions can essentially be explained when our perceptual assumption is not confirmed by the data, so our interpretation of the stimulus is inappropriate. Gregory (1970), (cited in Gross, 2005, pp 255) demonstrates good evidence for this view with a rotating hollow mask , where the mask can be seen hollow or normal. The assumption being selected is strongly influenced by past experience of faces. According to Gibson’s view of optic flow where the perception is seen as a result from interaction with the environment and also within movement it is possible to perceive that the mask is hollow. Therefore a weakness of Gregory’s´ theory is that it lacks ecological validity because it does not focus on everyday perception, but rare ‘abnormalities of perception’.
Evidence for Gregory’s view comes from demonstrations and visual illusions showing that conceptual knowledge affects the way in which simple visual phenomena can be perceived. Nevertheless, it does not explain how the knowledge for perception is acquired. In contrast Gibson has an alternative explanation with texture gradient and affordances.
Nevertheless, one of the most significant problems with Gibson’s theory is its inability to explain the Ames distorted room illusion (Gehringer & Engel , 1986). Gibson argues that most mistaken perception occurs in situations very different from those, which exist in the natural environment. However, to suggest that illusions are nothing but laboratory tricks designed to confuse people is not true, since at least some produce effects similar to those found in normal perception.
Despite the important differences between Gibson and Gregory’s theories, they agree on several points . Both believe that visual perception is mediated by light reflected from surfaces and objects, so we therefore need some kind of physiological system to perceive. They also agree that perception is an active process and that our perceptual experiences can be influenced by learning .
In conclusion , however, there are several major differences between the two theories. Gregory believes that memory ; habit, experience and so on must supplement meaningless sensory cues, in order to construct a meaningful world. In contrast Gibson argues that the environment (initially the optic array) provides us with all the information we need for living in the world. In most circumstances, both processes are essential as Neisser (1976) stressed in the analysis -by- synthesis model. And both theories explain different aspects of visual perception. When visual stimuli are present and visibility is good then technically the preferable theory is Gibson’s theory. On the other hand Gregory’s theory, however, may be most applicable when stimuli are incomplete or presented very briefly .
Reference:

Bruce, V. & Green, P.R. (1990) Visual Perception, 2nd ed. Hove: Erlbaum.

Gehringer, William L. & Engel, E. (1986). Human Perception & Performance . Journal of Experimental Psychology, 2, 181-185.

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

Gregory, R.L. (1980) Perception as hypothesis. Philosophical Transaction of the Royal Society of London, 290, 181-197

Gross, R. (2005). Psychology. The science of mind and behaviour, 5th ed. London: Hodder Arnold .

Neisser, U. (1976). Cognition and Reality . San Fransisco: W.H.Freeman
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