Hysteresis in the perception of motion direction

Abstract

A percept of global, coherent motion can be obtained by combining local motion vectors in a random-dot cinematogram.1 Extending this paradigm, the velocity vector field can be continuously altered over time, creating a display that changes from complete random notes to unidirectional flow or in the reverse direction. Using both types of vector-field change we measured the breakpoint—a marked transition in the percept, either from random to unidirectional motion or from unidirectional motion to random. These perceptual break-points exhibit marked hysteresislike behavior. Control experiments have ruled out eye movements as a possible cause for the hysteresis. The width of the hysteresis loop, as measured by the difference between the two types of breakpoint, scales with the density of dots in the display field but does not appear to depend on the size of the viewing aperture, suggesting a form of local cooperativity. Efforts have been made to interpret these and other results in the context of a 2-D Ising model for cooperative phenomena.