Re-evaluation of local adaptation for motion aftereffect.

Abstract

A motion aftereffect (MAE) can be induced by stimuli moving in surrounding areas. This suggests the relevance of mechanisms for relative motion, rather than early-level motion detectors, which are considered to work locally. Experiments are reported in which the role of local adaptation in the MAE with a stimulus configuration comprising relative motion has been discussed. Sinusoidal gratings were presented in three rectangular windows: a centre window, and two windows one above and one below the central one. The surrounding top and bottom windows, which were divided into left and right halves, had gratings presented in only one of the two halves. The MAE duration was measured after adaptation to motion either in the central or in the surrounding windows, by controlling the regions with the gratings. From this, the regions of surrounding gratings were found not to have a significant effect with adaptation in the centre window. With adaptation in the surrounds, however, these regions did affect the MAE; the MAE duration was reduced when the adapted region had no gratings in the test phase. Thus, for an MAE it is necessary for the adapted area to be covered with stimuli in the test phase, which indicates the dominance of local adaptation for the MAE even when relative motion is relevant in producing the MAE.