The role of orientation processing in the scintillating grid illusion.

In the scintillating grid illusion, illusory dark spots are perceived on white patches at the intersections of gray bars. Previous studies have suggested that processing related to the orientation of the bars plays a role in this illusion, but the specific underlying mechanisms are unclear. In the present study, we investigated the role of orientation processing across the intersection in generating the scintillating grid illusion. The results revealed that the illusion was attenuated when the patch was located at the intersection of short bars (Experiment 1), irrespective of the spatial distance between patches (Experiment 2). The local cruciform patterns determined the strength of the illusion, even when lateral offset of the patches was employed (Experiment 3). The illusion was observed even when a small spatial gap was introduced around the patches. A larger gap produced a weaker illusion (Experiment 4). Spatial offsets of the bars across the gapped intersection greatly reduced the illusion (Experiment 5). We discuss these findings with regard to the activity of S1-type simple cells that respond to the luminance along an oriented edge across the intersection.