Orientation detectors in the human visual system and figural aftereffects.

Figural aftereffects were measured by using square patches of high-contrast grating on a dark background as inspection and test figures. The orientation of the outer square border and the enclosed grating were varied independently in order to evaluate their relative influence on the strength of the induced change of overall apparent size of the test figure. The largest effect is obtained when inspection and test figures are identical in the orientation of both outer border and enclosed grating. The strength of the aftereffect is reduced as a difference in orientation is introduced between inspection and test figure for either the outer contour or the contained grating, although the former is a more potent factor than the latter.