Cortical dynamics of surface lightness anchoring, filling-In, and perception

Using afterimages for orientation and color to explore mechanisms of visual filling-in

Simulations of Grossberg's FACADE model of visual perception have previously been used to explain afterimage percepts produced by viewing a sequence of orthogonally oriented gratings. Additional simulations of the model are now used to predict new afterimage percepts. One simulation emphasizes that the afterimage percepts are the result of orientation afterresponses and color afterresponses that interact at a filling-in stage. We report experimental data that agree with FACADE's prediction. A second simulation emphasizes the properties of the model's filling-in stage and predicts a situation where the afterimage percept should not appear. We report experimental data indicating that this model prediction is incorrect. We argue that the model is unable to account for this result unless the filling-in stage mechanisms are different from a diffusive-type process. We propose an alternative mechanism, and simulations demonstrate the system's ability to account for the afterimage data.

Using afterimages to test neural mechanisms for perceptual filling-in

Many theories of visual perception propose that brightness information spreads from edges to define the perceived intensity of the interior of visual surfaces. Several theories of visual perception have hypothesized that this filling-in process is similar to a diffusion of information where the signals coding brightness spread to nearest neighbors. This paper shows that diffusive mechanisms fail to account for the characteristics of certain afterimage percepts that seem to be dependent on the filling-in process. A psychophysical experiment tests a key property of diffusion-based filling-in mechanisms and finds data that rejects this class of models. A non-diffusive based filling-in mechanism is proposed and is shown to act much like the diffusive based mechanism in many instances, but also produces afterimage percepts that match the experimental data.