Abstract
[Purpose] After the exposure to superimposed sinusoidal gratings with different spatial frequencies moving in the opposite directions, the motion aftereffect (MAE) of the high spatial frequency grating was seen with a static test while that of the low spatial frequency was seen with a flicker test. We interpreted the MAEs by assuming the slow and fast motion systems, showing difference in temporal frequency selectivity of MAE durations (Shioiri and Matsumiya, 2009). The purpose of the study is to confirm the assumption using a technique that can estimate contrast sensitivity of the systems with MAE. The technique varied contrast of either of the two superimposed gratings in adaptation to find the condition where no MAE was perceived. With varying temporal frequency of either grating, temporal tuning of each motion system was estimated. [Experiment] The spatial frequencies of the gratings were 0.53 c/deg and 2.1 c/deg. After 5 s of adaptation, the observer judged MAE direction in the stationary or the flicker (4 Hz) stimulus. Dependently on the response, the contrast of one of the gratings changed so that the MAE would be weaker. The contrast with no MAE was obtained with a stair case procedure. This provides the equivalent contrast of the grating to the fixed one of the other. Temporal frequency of the 2.1 c/deg (or 0.53 c/deg) grating was varied between 0.63 and 20 Hz in adaptation when the static (or flicker) test was used to investigate the MAE strength of the slow (or fast) motion system. [Results] The static and flicker MAEs showed different dependency of temporal frequency: the static MAE duration peaked at lower temporal frequency than the flicker MAE as has been shown with the MAE duration measurements. This indicates that the dependency of contrast sensitivity on temporal frequency is different between the two motion systems.