The perceptual coherence of moving visual patterns.

Two experiments evaluated the detectability of coherent motion as a function of the coherence and relative direction of motion of the background in which it occurred. The stimulus patterns consisted of sequential frames of randomly positioned dots that could be displaced relative to each other; their coherence was defined by the correlation between positions of dots in successive frames. When all of the correlated components were displaced in the same direction, the detectability of coherent motion of any given component was approximately independent of the coherence of the remainder of the pattern, and the perceived coherence of the whole pattern was proportional to its statistical coherence. Such performance is characteristic of linear system. When two superimposed lattices were displaced in opposite directioins, however, they were competitive in that increasing coherence of one direction decreased the detectability of coherent motion in the opposite direction. The latter results as well as those of other experiments indicate that the visual system is nonlinear. In general, the perceived coherence reflects the coherence of the stimulus patterns.