Corner salience varies linearly with corner angle during flicker-augmented contrast: a general principle of corner...

When corners are embedded in a luminance gradient, their perceived salience varies linearly with corner angle (Troncoso et al., 2005). Here we hypothesize that this relationship may hold true for all corners, not just corner gradients. To test this hypothesis, we developed a novel variant of the flicker-augmented contrast illusion (Anstis and Ho, 1998) that employs solid (non-gradient) corners of varying angles to modify perceived brightness. We flickered solid corners from dark to light grey (50% luminance over time) against a black or a white background. With this new stimulus, subjects compared the apparent brightness of corners, which did not vary in actual luminance, to non-illusory stimuli that varied in actual luminance. We found that the apparent brightness of corners was linearly related to the sharpness of corner angle. Thus this relationship is not solely an effect of corners embedded in gradients, but may be a general principle of corner perception. These findings may have important repercussions for brain mechanisms underlying the early visual processing of shape and brightness. A large fraction of Vasarely's art showcases the perceptual salience of corners, curvature and terminators. Several of these artworks and their implications for visual processing are discussed.