Chromatic induction from surrounding stimuli under perceptual suppression

The appearance of colors can be affected by their spatiotemporal context. The shift in color appearance according to the surrounding colors is called color induction or chromatic induction; in particular, the shift in opponent color of the surround is called chromatic contrast. To investigate whether chromatic induction occurs even when the chromatic surround is imperceptible, we measured chromatic induction during interocular suppression. A multicolor or uniform color field was presented as the surround stimulus, and a colored continuous flash suppression (CFS) stimulus was presented to the dominant eye of each subject. The subjects were asked to report the appearance of the test field only when the stationary surround stimulus is invisible by interocular suppression with CFS. The resulting shifts in color appearance due to chromatic induction were significant even under the conditions of interocular suppression for all surround stimuli. The magnitude of chromatic induction differed with the surround conditions, and this difference was preserved regardless of the viewing conditions. The chromatic induction effect was reduced by CFS, in proportion to the magnitude of chromatic induction under natural (i.e., no-CFS) viewing conditions. According to an analysis with linear model fitting, we revealed the presence of at least two kinds of subprocesses for chromatic induction that reside at higher and lower levels than the site of interocular suppression. One mechanism yields different degrees of chromatic induction based on the complexity of the surround, which is unaffected by interocular suppression, while the other mechanism changes its output with interocular suppression acting as a gain control. Our results imply that the total chromatic induction effect is achieved via a linear summation of outputs from mechanisms that reside at different levels of visual processing.

Perceiving Opponent Hues in Color Induction Displays

According to Hering's color theory, certain hues (red vs green and blue vs yellow) are mutually exclusive as components of a single color; consequently a color cannot be perceived as reddish-green or bluish-yellow. The goal of our study is to test this key postulate of the opponent color theory. Using the method of adjustment, our observers determine the boundaries of chromatic zones in a red–green continuum. We demonstrate on two distinct stimulus sets, one formed using a chromatic grid and neon spreading and the other based on solid colored regions, that the chromatic contrast of a purple surround over a red figure results in perception of 'forbidden' reddish-green colors. The observed phenomenon can be understood as resulting from the construction of a virtual filter, a process that bypasses photoreceptor summation and permits forbidden color combinations. Showing that opponent hue combinations, previously reported only under artificial image stabilization, can be present in normal viewing conditions offers new approaches for the experimental study of the dimensionality and structure of perceptual color space.

The Munker–White Effect and Chromatic Induction Share Similar Nonlinear Response Properties

The brightness or color appearance of a region may be altered by the presence of a pattern surrounding it in the visual field. The Munker–White effect (grating surround) and brightness or color induction from concentric annuli ('bull's-eye' surround) are two examples. We examined whether these two phenomena share similar properties. In the asymmetric matching experiment, the task of an observer was to adjust the appearance of a matching patch to match the appearance of a test patch embedded in one of the two types (square wave grating or concentric annuli) of inducing surrounds (inducers). The inducer modulated in one of three color directions (isochromatic: ±(L + M + S) and isoluminance: ±(L – M) or ±S). Each inducer type and color direction had two opposing phases and four contrast levels. The results show that the induced appearance shift increases as a power function of the inducer contrast, regardless of the spatial configuration of the inducer. Further analysis showed that a sensitivity modulation model of lateral interaction could explain both induction effects.

V1 Response Timing and Surface Filling-In

There is ample evidence from demonstrations such as color induction and stabilized images that information from surface boundaries plays a special role in determining the perception of surface interiors. Surface interiors appear to “fill-in.” Psychophysical experiments also show that surface perception involves a slow scale-dependent process distinct from mechanisms involved in contour perception. The present experiments aimed to test the hypothesis that surface perception is associated with relatively slow scale-dependent neural filling-in. We found that responses in macaque primary visual cortex (V1) are slower to surface interiors than responses to optimal bar stimuli. Moreover, we found that the response to a surface interior is delayed relative to the response to the surface's border and the extent of the delay is proportional to the distance between a receptive field and the border. These findings are consistent with some forms of neural filling-in and suggest that V1 may provide the neural substrate for perceptual filling-in.