Amodally completed angles

When the vertex of an occluded angle geometrically belongs to the side of the occluding surface, the occluded angle looks distorted. This characteristic effect of coincidental occlusion – called the Gerbino illusion – is consistent with the phenomenal rounding of angles observed under conditions of symmetrical occlusion. Both effects are robust and appear in static and dynamic displays. The Gerbino illusion differs from distortions observed in Poggendorff-like displays, runs against the tendency to global Prägnanz, and reveals important aspects of amodal completion processes. Alternative explanations based on visual interpolation and visual approximation are discussed. According to the approximation-based explanation the possible discrepancy between internal models and the sensory input is perceptually represented as a phenomenal distortion.