Velocity-sensitive elements in human vision: initial psychophysical evidence.

HUBEL and WIESEL (1962) described neurons in the mammalian visual system which respond most ~gorou~y to a contour moving through the visual field in a particnlar direction. With repeated stimulation, the response of such cells diminishes (BARLOW and HILL, 1963; HUBEL and WIESEL, 1965). Adaptation produced by prolonged viewing of uniformly moving contours has also been studied psychophysically with humans. For example, CARLSON (1962) has shown that the apparent velocity of a test contour is decreased signi8cantly by prior observation of contours moving in the same direction and was unaffected by observation of contours moving in the opposite direction. In a related study SEKULBR and GANZ (1963) found that observation of contours moving in one direction raises the threshold for a subsequently presented train of contours moving in the same direction. The parallels between these neurophysiological and psychophysical findings suggest that the human visual system contains elements which are direction-sensitive. Another char&e&tic of the direction-sensitive neurons in lower animals is their velocity sensitivity, i.e. a given neuron is maximally responsive to a particular rate of motion (BARJ_OW, HILL and LEVICK, 1964; HUBEL and W~~XL, 1965). We have attempted to learn whether, as might be predicted from the work on lower animals, different elements in human vision mediate the perception of contours moving at different velocities. Basically, we attempt to produce adaptation in elements responsive to a particular velocity of contour movement. We then observe the effects of this adaptation upon the threshold for the detection of contours moving at different velocities. The degree to which adaptation with one velocity of motion affects the detection of contours moving at another velocity can be used to indicate the extent to which common elements respond to both velocities.