Cocco M L, Pinna B, Spillmann L, 2000, "Illusory contours and neon colour spreading reconsidered in the light of Petter's rule" Perception 29 ECVP Abstract Supplement
Illusory contours and neon colour spreading reconsidered in the light of Petter's rule
M L Cocco, B Pinna, L Spillmann
A black pattern formed by two overlapping surfaces may segregate into its component patterns separated by an illusory contour. Typically, the surface with the shorter contours appears in front of the larger one (Petter's rule, PR).
We studied PR for illusory contours (ICs) and neon colour spreading (NCS) to test the hypothesis that contour formation determined by PR can affect the presence/absence, the strength, and the appearance in depth of ICs and NCS. In the cases of ICs or NCS induced by lines, PR determines the contour orientation (same or perpendicular) abutting a line end. In the 'same' condition, ICs and NCS should be absent. In the 'perpendicular' condition, both ICs and NCS should be strong. Medium strength would be expected for ambiguous orientations. Eight experiments were carried out to test cognitive theories, and computational theories based on interactions at line-ends. The inducing stimuli were interrupted parallel lines, and we varied the thickness of lines, the spacing between lines, and the magnitude of the gap between line-ends.
Results show that both ICs and NCS follow PR. It is proposed that PR derives from the formation of two different kinds of contours, modal and amodal, linked to the dynamics of filling-in of contour gaps.
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