Ambiguous plaids: switching between coherence and transparency.

Abstract

A plaid pattern consisting of two differently oriented moving gratings can be seen as two alternative percepts: transparency, in which the two gratings are seen to slide over each other in their respective directions, or coherence, in which one integrated pattern (the plaid) is seen to move in a new direction. With prolonged inspection, an observer switches between these two alternatives. It was found here that adaptation to unambiguous coherence reduces the time that coherence is seen with an ambiguous test stimulus. Similarly, adaptation to transparency reduces the time transparency is seen. Analysis of the duration of consecutive episodes revealed that the underlying processes are adapted independently. Control experiments confirmed that adaptation occurred to the coherent plaid and not to the intersections, and that this adaptation was not simply a directional motion aftereffect. It is concluded that switching occurs between motion processes at different cortical levels that can be adapted independently.