Invariance to low-level features and partial transfer over space in the tilt aftereffects evoked by symmetrical patterns

The symmetry axis is the midline that divides a pattern into congruent halves, which is physically nonexistent but evokes tilt aftereffect (TAE). To investigate the cortical correspondence of the symmetry axis, we examined the invariance of symmetry-induced TAE with regard to low-level visual features and the spatial transfer of TAE over visual fields. When the adaptation pattern was rotated and changed sequentially with the orientation of the symmetry axis unchanged, the measured TAE decreased only slightly (18%) compared to stationary patterns. This effect persisted when the adaptation and test patterns were presented in different visual fields. These results indicate that the cortical representation of symmetry is generated independently of low-level features and involves higher-level visual areas.