An efferent component in the visual perception of direction and extent.

Abstract

After outlining the history of motor theories of visual perception, a new theory linking information extraction patterns, specifically adapted for the guidance of eye movements, to the visual perception of direction and extent is presented. Following a brief discussion of comparative and physiological considerations, a research strategy to test for efferent involvement in visual perception in humans is presented. In seven demonstration experiments, predictions from efferent considerations are used to create a new set of illusions of direction and extent and to demonstrate new predictable variations in the magnitude of some classical illusion figures. Another demonstration illustrates that systematic changes in visual perception occur as a function of changes in motoric demands, even in the absence of any configurational changes in the stimulus. A final section shows the relationship between attention and efferent readiness and their interaction in the formation of the conscious visual percept.From a historical perspective, most contemporary theories of visual perception are quite conservative. This conservatism springs from an apparent acceptance of the premise that any proper analysis of visual experience must avoid reference to nonvisual mechanisms, except for labeling and semantic aspects of the perceptual process. It follows that most visual theorists tend to derive virtually every aspect of the conscious percept solely from either the physical characteristics of the visual stimulus array or the operation of readily definable neurological units in the visual system.Characteristic of the former viewpoint is Gibson's (1979) theory of ecological optics, which maintains that virtually all aspects of the final percept are predictable from invariants in the stimulus array. Current attempts to derive the conscious percept from a hypothesized Fourier analysis occurring within the visual system are similar in approach, merely relying on higher level processing of the physical stimulus (e.g., Weisstein & Harris, 1980). Using the current literature as an index, the only seemingly acceptable alternative to derivation of the final percept directly from physical stimulus properties is to adopt a neuroreductionist approach. Here the investigator is expected to isolate specific neural units or channels that are then held to account for each aspect of the the final subjective percept (e.g., Graham, Robson, & Nachmias, 1978;Hubel, 1978). Although the above-mentioned approaches have a certain allure, providing concrete mechanisms and clearly calculable stimulus parameters on which to rest conclusions, there are some alternative theoretical treatments of visual perception, which do allow This research was supported in part by grants from the National Science and Engineering Research Council of Canada. loo many people have helped shape the ideas contained in this article to be acknowledged separately. However, two who deserve special thanks are Clare Porac and Joan S. Girgus.

The Ponzo illusion and the perception of orientation

“…The Müller-Lyer illusion generally increases monotonically as the angle becomes more acute (as long as the shaft lines are not too long), whereas the strength of the Ponzo illusion first increases, then decreases with the angle. Finally, Coren (1986) has shown that it is not the angle between the shaft and the arrowheads that is critical, but how far from the shaft the arrowheads extend. Longer arrowheads and more acute angles are equivalent in their effect on the Müller-Lyer illusion.…”

Length distortion of temporally extended visual displays: Similarity to haptic spatial perception

“…However, it should also be noted that reafference from motor commands appears to provide information about eye movements, leaving open the possibility of a contribution of the movement system (Helmholtz, 1867(Helmholtz, /1962). Coren's (1986) work also demonstrates that even readiness for eye movemeqts can have a substantial effect on visual perception, vendical or illusory. (For a review of the relation of eye movements to visual localization, see Matin, 1986.…”

Tool use and the effect of action on the imagination.

“…Coren (1986), for example, showed that saccadic eye movements are responsible for the Mueller-Lyer optical illusion. The present experiments offered evidence that action can also influence the imagination.…”