Amodal completion versus induced inhomogeneities in the organization of illusory figures.

An analysis is presented of a phenomenological model of illusory contours. The model is based on amodal completion as the primary factor giving rise to the illusory figure. In the experiment, conducted by the method of paired comparisons, the same parameter was manipulated in two series of equivalent configurations. The first series yielded examples of amodal completion, the second examples of illusory figures. Three groups of subjects evaluated the magnitude of completion, the brightness contrast of the illusory figure, and the contour clarity of the illusory figure. A control experiment was conducted, which demonstrated that in these configurations amodal completion and amodal continuation behave in the same way. Line displacement did not influence the brightness or the contour clarity of the illusory figures, though it influenced the magnitude of amodal completion. These results are in agreement with the energetic model developed by Sambin.

A dynamic model for anomalous figures: the shape of line-induced brightness modifications.

It is recognized that a fundamental role in the perception of anomalous figures is played by the intensity and shape of brightness modifications induced by line ends. The aim of this work was to study the structure of these modifications experimentally, by using variously arranged dots as probes. It was thus assumed that dots can measure activations generated inside abrupt line ends. The results show distribution of activation which differs according to dot distance and angle with respect to the continuation of the line near its end. These data do not agree with the predictions of information processing models in the literature on anomalous figures, which are based on perceptually postulated figures accounting for unlikely gaps. However, they do agree with the dynamic model proposed here, which is based on the idea that certain figure characteristics, eg the differential brightness of anomalous figures, depend on activation distribution which in turn depends on the organization of the forces in play. This idea is rooted in Gestalt theory. Another model supported by our experimental data is Grossberg's neural dynamic approach. In this case too, the basic idea is that of activation distribution which depends on the interaction of complex neural networks functioning according to special algorithms.