Abstract
A new filling-in model is proposed in order to account for challenging brightness illusions, where inducing background elements are spatially separated from the gray target such as dungeon, cube and grating illusions, bullseye display and ring patterns. This model implements the simple idea that neural response to low-contrast contour is enhanced (facilitated) by the presence of collinear or parallel high-contrast contours in its wider neighborhood. Contour facilitation is achieved via dendritic inhibition, which enables the computation of maximum function among inputs to the node. Recurrent application of maximum function leads to the propagation of the neural signal along collinear or parallel contour segments. When a strong global-contour signal is accompanied with a weak local-contour signal at the same location, conditions are met to produce brightness assimilation within the Filling-in Layer. Computer simulations showed that the model correctly predicts brightness appearance in all of the aforementioned illusions as well as in White's effect, Benary's cross, Todorović's illusion, checkerboard contrast, contrast-contrast illusion and various variations of the White's effect. The proposed model offers new insights on how geometric factors (contour colinearity or parallelism), together with contrast magnitude contribute to the brightness perception.
Highlights
Simultaneous brightness contrast, in which a gray target appears brighter when surrounded by black than a gray target surrounded by white, suggests that brightness perception is not determined solely by the luminance of the target but depends on the luminance of the surrounding region as well
The effect of Boundary Contour System (BCS) output attenuation is to allow the filling-in of brightness signals across those edges where contour facilitation occurs in BCS. This activity spreading in Feature Contour System (FCS) simulates the effect of assimilation which opposes the effect of the local contrast computed along the low-contrast edge
The second part shows that the same assimilation effect arises when contours are arranged in parallel
Summary
Simultaneous brightness contrast, in which a gray target appears brighter when surrounded by black than a gray target surrounded by white, suggests that brightness perception is not determined solely by the luminance of the target but depends on the luminance of the surrounding region as well. This activity spreading in FCS simulates the effect of assimilation which opposes the effect of the local contrast computed along the low-contrast edge. Threshold for the L/G Interaction removes completely Boundary Contour representation of the horizontal edges of gray square Such removal of the Boundary Contour signals will produce activity spreading (assimilation) within the Filling-in Layers. In FCS, filling-in enables the brightness signals to spread until they are blocked at the luminance borders by the output of BCS (i.e., the output of L/G Interaction) These Boundary Contour signals are effective in preventing filling-in only when they are complete, that is, when they cover all edges of the surface. The computational analysis of natural image statistics suggests that colinearity and parallelism are both relevant factors (Kruger, 1998). Yen and Finkel (1998) included both, collinear and parallel projections in a model of contour integration in order to achieve better contour detection
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