Rapid Figure – Ground Responses to Stereograms Reveal an Advantage for a Convex Foreground

Convexity has long been recognised as a factor that affects figure – ground segmentation, even when pitted against other factors such as symmetry [Kanizsa and Gerbino, 1976 Art and Artefacts Ed.M Henle (New York: Springer) pp 25–32], It is accepted in the literature that the difference between concave and convex contours is important for the visual system, and that there is a prior expectation favouring convexities as figure. We used bipartite stimuli and a simple task in which observers had to report whether the foreground was on the left or the right. We report objective evidence that supports the idea that convexity affects figure – ground assignment, even though our stimuli were not pictorial in that depth order was specified unambiguously by binocular disparity.