Orientation masking and the tilt illusion with subjective contours.

Exposure to one edge renders another edge less visible as a function of relative orientation. Experiment 1 showed that orientation-selective masking occurs between phenomenal edges located at sites where the visual display is homogeneous (subjective contours) as well as between edges defined in terms of luminance discontinuity (real edges). In addition, real contours can be masked by subjective contours, and vice-versa. In experiment 2 it was found that the tilt illusion (apparent expansion of the angle formed by intersecting lines) can be induced with subjective as well as with real contours. These results suggest that it is inappropriate to attribute the perception of real and subjective contours to fundamentally different processes.