Differential familiarity effects in amodal completion: support from behavioral and electrophysiological measurements.

We studied the effects of learning on amodal completion of partly occluded shapes. Amodal completion may originate from local characteristics of the partly occluded contours, resulting in local completions, or from global characteristics, resulting in global completions. Two classes of occlusion patterns were constructed: convergent occlusion patterns, in which global and local completions resulted in the same shape, and the much more ambiguous divergent occlusion patterns, in which these completions resulted in different shapes. We used a sequential matching paradigm and obtained behavioral responses (Experiment 1s and 2) and electroencephalogram recordings (Experiment 3) to investigate whether previously learned shapes influenced completions of partly occluded shapes. Experiment 1 revealed the preference for different completions of both occlusion patterns. In Experiment 2, learning effects were found only for test shapes following divergent occlusion patterns. Experiment 3 showed differential effects with regard to convergent and divergent occlusion patterns on a positive event-related potential in the 150- to 300-ms range, before learning. After learning, modulation of this effect was only found for the divergent occlusion patterns. The results show that amodal completion of shapes can be influenced by a simple learning task when multiple completions of partly occluded shapes are perceptually plausible.