Current interpolation models do not consider concavity/convexity as a factor that modulate the trajectory of amodally-completed contours. We ran 3 experiments using a simultaneous length comparison and probe localization, with pictures vs. random dot stereograms. Results indicate that contour polarity affects the amodally-completed angles of regular and irregular surfaces. As predicted by the minimal area hypothesis, image contours are less extrapolated when the amodal portion is convex rather than concave. The field model of interpolation (Fantoni & Gerbino 2003) has been revised to explain area minimization as an effect of surface support ratio.
