The Relationship Between Spatial Filtering and Subjective Contours

Abstract

The Kanizsa triangle represents a class of illusions that provide contours that are perceived but are not physically present in the original object. The question arises as to what visual processes, e.g., physical or cognitive, govern the visibility of subjective contours. Spatial filtering based on visual physiology has been shown to create physical intensity distributions from the Kanizsa triangle that generally correspond to the shape of the subjective contour (Ginsburg, 1975), which suggests that the basis for subjective contours may be physical rather than cognitive. This view was questioned by Tyler (1977), who noted that an outline version of the Kanizsa triangle also exhibited a subjective contour. However, examination of computer plots of the digitally filtered subjective contours of both the solid and outline triangles reveals a less well-defined subjective contour and reduced low spatial frequency energy from the outline triangle (Fig. 13.1).Both the reduce magnitude spectra and the less well-defined subjective contour predict a decreased perceived subjective contour for the outline triangle.