Effect of central and surrounding gratings of test stimulus on appearance of motion aftereffect

We conducted three experiments to examine the effect of spatial arrangement of test stimulus on the motion aftereffect (MAE). The adaptation and test stimuli were presented to subjects successively. Each adaptation stimulus consisted of a set of three gratings; a central stationary grating was located between the two surrounding gratings, one above and the other below respectively, which were arranged to move leftward for two minutes. The location and/or the shape of the test stimulus were varied to examine the effects of the spatial arrangement. The first and second experiments revealed that the MAE lasted longer when the surrounding gratings for the test were superimposed on those for the adaptation than when they were not superimposed. Further, the results of both experiments showed that the duration was not affected by the distance between the central grating and surrounding one. The results of the third experiment showed that the MAE lasted longer when the central grating for the test was identical with that for the adaptation than when not, and that the surrounding for the test need not to be identical with that for the adaptation. These results support Wade's hypothesis for explaining how MAE occurs.