Visual Processing of Object Velocity and Acceleration

Six separate projects have explored how velocity and acceleration are encoded in the human visual system. (1) Welch demonstrated speed discrimination for coherent plaid patterns formed of two superimposed gratings was limited by the speed of the gratings, not the apparent speed of the plaid itself. (2) Bowne et al. and more recently Grzywacz, applied 'motion-energy' models to the psychophysics of speed discrimination. (3) McKee and Welch compared the relative precision of velocity and size constancy, finding little evidence for velocity constancy in human motion processing. (4) Watamaniuk demonstrated that the visual system integrates diverse speeds (2-8 deg/sec) in a random dot display to obtain a precise estimate of the mean speed. (5) McKee and Watamaniuk found that a single point (the signal) moving in apparent motion (the noise), even though the spatial and temporal characteristics of the signal and noise points were identical on a frame-by-frame basis. (6) Bravo and Watamaniuk showed the two sets of randomly distributed dots moving in the same direction, but at two very different speeds, formed two transparent planes; discrimination of small changes in the speed of one set of dots was unaffected by the presence of the other dots.