Interaction of surface pattern and contour shape in the tilt after effects evoked by symmetry.

Integration of multiple properties of an object is a fundamental function of the visual cortex in object recognition. For instance, surface patterns and contour shapes are thought to be crucial characteristics that jointly contribute to recognition. However, the mechanisms of integration and corresponding cortical representations have not been fully clarified. We investigated the integration of surfaces and shapes by examining the tilt after effects (TAEs) evoked by the symmetry of patterns and contours. As symmetry in both pattern and contour evokes TAEs, we can directly measure the interaction between the two. The measured TAEs exhibited mutual transfer between the symmetry of the pattern (SP) and that of the contour shape (SS), i.e., adaptation by SP (SS) evoked TAEs when tested by SS (SP), suggesting the existence of an integrated representation. Next, we examined the interaction between SP and SS when both were simultaneously presented in adaptation. Congruent adaptors wherein their symmetry axes aligned evoked compressive interaction, whereas incongruent adaptors wherein the axes of SP and SS tilted to the opposite directions evoked subtractive interaction. These results suggest the existence of a cortical representation that integrates the properties of the surface and shape with suppressive interactions, which can provide crucial insights into the formation of object representation as well as the integration of visual information in the cortex.

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.