Visual processing of moving stimuli.

This review covers a period bracketed by two OSA Symposia--"Vision under Stabilized Image Conditions," held in San Francisco in 1978, and "Motion and Vision in Man and Machine," held in New Orleans in 1983--during which image stabilization came of age as a standard technique of visual psychophysics. It seems clear that the first spatiotemporal signal-processing step in the visual system depends on image motion; e.g., a constant velocity effectively provides the mathematical convolution of stimulus patterns with retinal receptive fields. Thus the motion of the stimulus pattern at the retina is an important experimental variable over which we have only recently gained full control. We can now replace the haphazard behavior of the subject's natural eye movements by simpler forms of motion that are known and controlled by the experimenter. Results obtained in our laboratory with such stabilized fixation control include threshold measurements for moving lines and gratings, comparison of contrast sensitivities with natural and artificial eye movements, effects of orientation on moving-grating thresholds, models of the stabilized spatiotemporal threshold surface, and effects of retinal inhomogeneity on selectivity for spatial frequency and velocity. Other experiments, too numerous to include here, have also used these techniques.