The structure of the human motion detection system
Andrea J. van Doorn, Jan J. Koenderink · IEEE Transactions on Systems Man and Cybernetics · 1983
In contradistinction with technical pattern recognizers, humans are very apt at the detection of regions of coherent movements in changing images. They detect coherent patches in spatiotemporal white noise at threshold signal-to-noise ratios of one hundredth! Possible physiological mechanisms that sustain 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 completely unlike the speedometer in an automobile: they are tuned, and a whole ensemble of mechanisms, tuned to different velocities, reside at any location in the visual field. Thus you 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 these units are found: these limit the resolution in time and space, whereas the 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.