Coherent global motion percepts from stochastic local motions.

A percept of global, coherent motion results when many different localized motion vectors are combined. We studied the percept with dynamic random dot kinematograms whose elements took independent, random walks of constant step size; their directions of displacement were drawn from a uniform distribution. The tendency to see global, coherent flow along the mean of the uniform distribution varied with the range of the distribution. Psychometric functions were obtained with kinematograms having various step sizes and element densities. The changes in the psychometric function with step size and density are consistent with Ullman's "minimal map theory" of motion correspondence.