The structure of the human motion detection system

Unlike technical pattern recognizers, humans are adept at the detection of regions of coherent movements in changing images. Possible physiological mechanisms for this ability are discussed in terms of simple mechanistic models, and the results of psychophysical experiments are presented. These results are compatible with two different mechanistic interpretations. The main result is that the human movement detectors are tuned, and a whole ensemble of mechanisms, tuned to different velocities, reside at any location in the visual field. Thus an observer may easily see two velocity vectors simultaneously at a given place. Segregation occurs when different detectors are stimulated at each side of a border. The spatiotemporal parameters that characterize the units limit the resolution in time and space, whereas sensitivity depends on the number of units that participate in a detection. This number may range between a few (perhaps one) to a thousand or more. Apparently, resolution can be traded against noise immunity. It is argued that technical systems developed on a similar basis might be useful as preprocessors of sequences of images in order to detect features of interest (coherent regions) and to suggest a first rough image segmentation.