Although the study of visual perception has made more progress in the past 40 years than any other area of cognitive science, there remain major disagreements as to how closely vision is tied to cognition. This target article sets out some of the arguments for both sides (arguments from computer vision, neuroscience, psychophysics, perceptual learning, and other areas of vision science) and defends the position that an important part of visual perception, corresponding to what some people have called early vision, is prohibited from accessing relevant expectations, knowledge, and utilities in determining the function it computes - in other words, it is cognitively im- penetrable. That part of vision is complex and involves top-down interactions that are internal to the early vision system. Its function is to provide a structured representation of the 3-D surfaces of objects sufficient to serve as an index into memory, with somewhat differ- ent outputs being made available to other systems such as those dealing with motor control. The paper also addresses certain concep- tual and methodological issues raised by this claim, such as whether signal detection theory and event-related potentials can be used to assess cognitive penetration of vision. A distinction is made among several stages in visual processing, including, in addition to the inflexible early-vision stage, a pre-per- ceptual attention-allocation stage and a post-perceptual evaluation, selection, and inference stage, which accesses long-term memory. These two stages provide the primary ways in which cognition can affect the outcome of visual perception. The paper discusses argu- ments from computer vision and psychology showing that vision is "intelligent" and involves elements of "problem solving." The cases of apparently intelligent interpretation sometimes cited in support of this claim do not show cognitive penetration; rather, they show that certain natural constraints on interpretation, concerned primarily with optical and geometrical properties of the world, have been com- piled into the visual system. The paper also examines a number of examples where instructions and "hints" are alleged to affect what is seen. In each case it is concluded that the evidence is more readily assimilated to the view that when cognitive effects are found, they have a locus outside early vision, in such processes as the allocation of focal attention and the identification of the stimulus.

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Is vision continuous with cognition? The case for cognitive impenetrability of visual perception

The Topography of Vision in Mammals of Contrasting Life Style: Comparative Optics and Retinal Organisation

Orientation judgments are more accurate at the horizontal and vertical orientations, possibly reflecting a statistical inference. Here the authors provide evidence for this idea, finding that observers' internal models for orientation match the local orientation distribution measured in photographs, and suggest how such information could be encoded in a neural population.

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Stuart Appelle

Papers

Perception and discrimination as a function of stimulus orientation: The "oblique effect" in man and animals.