Visual Psychophysics of Egomotion
Interim rept. 1 Feb 1992-31 Jan 1993
JOHNS HOPKINS UNIV BALTIMORE MD SCHOOL OF MEDICINE
Pagination or Media Count:
One study investigated, under two viewing conditions, an observers ability to determine whether she was moving forward along a straight or curved path using simulations of optic flow patterns. In one condition, the retinal image was stabilized against the effects of eye movements, in the other condition, eye movements were unrestricted. Stabilizing the retinal image decreased performance at slow speeds. A second study further explored the role of eye movements in the perception of motion. Speed-difference thresholds were measured under conditions of stabilized and free-viewing conditions. Despite the fact that eye movements can alter the direction and speed of the retinal-image motion relative to the stimulus motion, observers were able to judge speed differences in the free-viewing condition as well as in the stabilized-viewing condition, with the exception of the slowest speed. At the slowest speed, observers were able to detect smaller speed differences in the free-viewing condition. A third study determined the optimal stimulus for motion detection by searching the spatiotemporal stimulus whose direction was identified with least contrast energy. The best stimulus was determined to be at 3 cyclesdeg,1.67 degs with bandwidths of 7.06 Hz and 1 - 0.5 octaves.