Contribution of transient and sustained responses to the perception of apparent motion

The likelihood of seeing apparent motion (AM) was measured as a function of inter-stimulus-interval (ISI) between two isolated Gabor patches separated by 4 deg with spatial frequency (0.75, 2.0 and 4.5 c/deg) and exposure duration (33 and 1000 msec) as parameters. For the short stimuli, the likelihood of AM for the low-spatial-frequency of 0.75 c/deg was higher than that for the high-spatial-frequency of 4.5 c/deg, but for the long stimuli, the former was similar to, or lower than the latter. Decreasing the mean luminance from 190 to 0.8 cd/m2 impaired AM for the short stimuli of 2.0 c/deg, but improved AM for the long stimuli. The dependencies of AM on spatial frequency, exposure duration and adaptation level may be ascribed to the changing contribution of the transient and the sustained responses.