Motion Perception as an Area Process

Motion is perceived whenever a subject is presented with an appropriate spatiotemporal visual pattern. Like many other visual tasks, motion perception involves both local and global processing, and thus might be subject to the well known paradox that arises from the fact that local features and observations form the basis for global perception, but sometimes this global percept can not be easily derived from any single local observation, as is best exemplified by the aperture problem. Globally, dual (transparent) motion can be readily perceived. In this paper, we look for the spatial limits on the local ability to perceive multiple motion. Using the framework of apparent motion, we have found that dual, orthogonally oriented motion can be perceived only when the dots that constitute the two motions are separated by some spatial limit. For short range apparent motion, we have found that the limit is comparable to D max , which is the spatial limit on short range apparent motion and that the visual system can not perceive more than a single coherent motion in a local “patch” of radius D max . We have also found that this spatial limit on local motion perception is not constant, but depends linearly on the spatial organization of the stimuli, and vanishes for stimuli having reverse contrast. We compare the lower bound on the ability to perceive multiple motion to some well known bounds in stereopsis, and propose a cortical architecture that might account for it.