Abstract

MANY cells in the visual systems of lower animals are specialized to respond maximally to specific stimulus configurations or events. For example, some units respond vigorously to a border or edge in a particular orientation, but are unresponsive to that same border after it has been rotated through some angle. Other units respond selectively to objects which move through their receptive fields in different directions. While these "tuned" units vary considerably in the particular stimulus attribute or combination of attributes to which they are responsive, almost all of them seem to share two general properties. First, these units are unresponsive to homogeneous illumination of their receptive fields. Second, while they are not sensitive to the quantity of uniformly distributed light, their responses are influenced by changes in the contrast of their "preferred " stimuli. As a result of the contrast sensitivity of these units, systematic variation of stimulus contrast should be considered a major tool for studying the response characteristics of similarly "tuned " elements in human vision. Consequently, in the present experiments, the contrast of an adaptation stimulus was varied to control its visual effectiveness. The functional components of the response to that adaptation stimulus were identified by an examination

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