Abstract
[Purpose]
We report a new type of motion aftereffect. The stimulus consists two overlapped sinusoidal gratings with different spatial frequencies. When the two gratings move in the opposite directions one from the other, motion of the low spatial frequency grating is seen. After the exposure to the moving stimulus, however, however, motion aftereffect (MAE) is seen in the opposite direction of unperceived motion of the high spatial frequency grating (high spatial frequency superiority of motion aftereffect). To investigate the underlying mechanism of the phenomenon, we measured MAE duration with variable combinations of spatial frequencies.
[Experiment]
Adaptation stimulus consisted two drifting gratings with different spatial frequencies, which moved in the opposite directions. The contrast of each grating was 30 times of the threshold contrast. The spatial frequency of one grating was fixed at 0.53 c/deg and the other varied between 0.13 and 2.13 c/deg. After 20 s of adaptation, the observer judged MAE duration in the stationary or the flicker (4 Hz) stimulus of the same gratings, by pressing one of two keys to indicate the disappearance of MAE and the direction of perceived motion.
[Results]
Stationary test showed high spatial frequency superiority of MAE whereas flicker test showed opposite results, i.e., MAE in the direction opposite to the low spatial frequency drifting grating.
[Discussion]
The results suggest that there are two motion mechanisms. One is sensitive to low spatial and high temporal frequencies and the other is sensitive to high spatial and low temporal frequencies.