Abstract
Adaptation to a distorted face (e.g. expanded) induces a negative aftereffect (e.g. contracted) in the original face. Previous studies have shown that these aftereffects are comparable for upright and inverted images, but have not controlled whether the distortion itself shows an inversion effect. We directly tested whether differences in adaptation are tied to differences in recognition, by using a contingent aftereffect in which observers are simultaneously adapted to opposite distortions in two different faces (e.g. expanded face A vs. contracted face B). For distinct upright faces this leads to opposite aftereffects depending on face identity. We examined whether this contingency is reduced for two faces that become less distinguishable when inverted. Face pairs consisted of an original frontal-view image and a Thatcherized version with mouth and eyes rotated, changes which are very salient in upright faces while difficult to discern in inverted faces. Subjects adapted to a contracted version of one alternated with an expanded version of the other at a rate of 1 sec/image. A 2AFC staircase was then used to null the perceived distortions in either face. Upright faces showed a contingent aftereffect between the original and Thatcherized face. This effect was weaker for the inverted face pair, though not for all subjects, a difference which could reflect differences in which aspects of the images were used to judge the distortions. Such effects are consistent with the possibility that face adaptation can show an inversion effect when inversion reduces sensitivity to the stimulus dimensions controlling the adaptation.