The aftereffect of a spatial offset between Gabor patches depends on carrier orientations

This study explored the orientation connectivity in a contrast modulation processing mechanism, modeled as two filtering stages with nonlinear processing in between, by investigating how a negative aftereffect of a contrast-defined spatial offset is influenced by carrier orientations in the adapting stimulus. After adaptation to multiple, globally presented pairs of Gabor patches with a specific horizontal offset, subjects perceived a vertically aligned test pair of patches as offset in the orientation opposite to that of the adaptor. Although the orientations of the carrier gratings in the adaptor pairs were irrelevant to the task, the aftereffect magnitude depended on them. A large aftereffect was observed when the carrier orientations were parallel and/or perpendicular to the contrast-defined orientation, supporting the notion that second-stage filters receive strong inputs from first-stage filters with parallel and perpendicular orientation preferences. Furthermore, the aftereffect was also large when the carrier for only one patch was parallel or perpendicular, and no significant difference in the aftereffect magnitude was observed whether the adaptor pair contained one or two such patches. These results suggest that connectivity is not strictly selective to parallel and perpendicular relationships. Spatially heterogeneous connectivity might explain the observed effect.