Amodal Completion, Depth Stratification, and Illusory Figures: A Test of Kanizsa's Explanation

Subjective contours have been explained by Kanizsa as being a consequence of amodal completion of incomplete figures. According to the theory of amodal completion, figural incompleteness triggers the emergence of an illusory object superimposed on the gaps in the inducers, which in turn hide parts of the pattern, thus suggesting that the plane of the illusory object must always be seen to be above the plane of the inducers. A figure was created in which subjective contours are seen despite the fact that the perceived depth relationships run counter to that required by the theory of amodal completion. In four experiments, this depth relationship is confirmed by using direct and indirect measures which assess both registered and apprehended depth. By emphasizing a logical inconsistency in the explanation based on amodal completion, the results show that amodal completion, at least in Kanizsa-like patterns, cannot be considered as a causal factor for subjective contour figures.