Academic journal article Perception and Psychophysics

Using Afterimages for Orientation and Color to Explore Mechanisms of Visual Filling-In

Academic journal article Perception and Psychophysics

Using Afterimages for Orientation and Color to Explore Mechanisms of Visual Filling-In

Article excerpt

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.

Part of the construction of visual percepts seems to involve a filling-in process that computes information about perceived colors and brightness across surfaces (Gerrits & Vendrik, 1970; Pessoa, Thompson, & Noë, 1998). Illusions such as neon color spreading and the water-color illusion (da Pos & Bressan, 2003; Pinna, Brelstaff, & Spillmann, 2001) have been taken as direct evidence of filling-in. Filling-in processes have also been invoked to explain a variety of other percepts, including brightness perception (Grossberg & Todorovic, 1988; Todorovic, 1987), properties of McCollough afterimages (Broerse, Vladusich, & O'Shea, 1999; Grossberg, Hwang, & Mingolla, 2002), properties of color complement afterimages (Shimojo, Kamitani, & Nishida, 2001), and some aspects of 3-D perception (Grossberg, 1997).

Although there is agreement in some circles that filling-in mechanisms exist, the details of those mechanisms are unclear. The standard view is that the filling-in process is similar to an isotropic diffusion of information, from edges to interiors of regions (Gerrits & Vendrik, 1970). Consistent with this idea, Paradiso and Nakayama ( 1991 ) demonstrated that a circular mask appeared to block the diffusive spread of brightness information (see also Arrington, 1994; Stoper & Mansfield, 1978). Neurophysiological evidence on filling-in mechanisms has been unclear. Early reports on the representation of edge and surface information in area V1 of monkeys suggested that whereas edges were coded by orientation-sensitive neurons, color-sensitive neurons were not orientationally tuned (e.g., Livingstone & Hubel, 1984). This has been taken as evidence for an anatomical segregation of form (edges) and surface (color) information in visual cortex. Komatsu, Kinoshita, and Murakami (2000) measured activity from cells responding to a homogeneous pattern that covered the blind spot, which implies the presence of a filling-in mechanism. Generally, these findings are consistent with a diffusive filling-in mechanism for surface brightness and color. However, Friedman, Zhou, and von der Heydt (2003) report evidence that many color-sensitive cells are also highly orientation selective. Friedman et al. argue that current neurophysiological evidence no longer supports the hypothesized anatomical separation of form and color information. The orientation sensitivity of neurons supporting a filling-in mechanism seems contrary to isotropic diffusion of color and brightness that is part of most filling-in theories.

Perhaps the most advanced model that incorporates a filling-in process is the FACADE (form and color and depth) model proposed by Grossberg and colleagues (Cohen & Grossberg, 1984; Grossberg, 1987, 1997; Grossberg & Mingolla, 1985a, 1985b). In this model, a feature contour system (FCS) includes a diffusive filling-in process that computes and distributes brightness and color information across a region, but the filling-in is restricted by signals from a boundary contour system (BCS) that block the filling-in process from spreading into adjacent regions. …

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