Motion Aftereffect after Adaptation to Transparent MOtion Depends on Stimulus Contrast and Speed.

Characteristics of motion aftereffect (MAE) following adaptation to two dot-populations moving in orthogonal directions at different speeds are reported. The results of experiments indicate that: (1) when the contrast of test stimuli (randomly moving dots presented after adapting stimuli) is high, the perceived direction of MAE inclines toward the opposite direction of the population which is closer in speed to the test stimuli than the other; (2) when the test contrast is low, the MAE direction is not so much depend on test speed and inclines toward the opposite direction of the population whose speed is more dominant in human sensitivity than that of the other. Simple assumptions based on physiological findings enable us to account for the complex results.