Dissociation of color and figure–ground effects in the watercolor illusion

Abstract

Two phenomena can be observed in the watercolor illusion: illusory color spreading and figureground organization. We performed experiments to determine whether the figure-ground effect is a consequence of the color illusion or due to an independent mechanism. Subjects were tested with displays consisting of six adjacent compartments, three that generated the illusion alternating with three that served for comparison. In a first set of experiments, the illusory color was measured by finding the matching physical color in the alternate compartments. Figureness (probability of 'figure' responses, 2AFC) of the watercolor compartments was then determined with and without the matching color in the alternate compartments. The color match reduced figureness, but did not abolish it. There was a range of colors in which the watercolor compartments dominated as figures over the alternate compartments although the latter appeared more saturated in color. In another experiment, the effect of tinting alternate compartments was measured in displays without watercolor illusion. Figureness increased with color contrast, but its value at the equivalent contrast fell short of the figureness value obtained for the watercolor pattern. Thus, in both experiments figureness produced by the watercolor pattern was stronger than expected from the color effect, suggesting independent mechanisms. Considering the neurophysiology, we propose that the color illusion follows from the principles of representation of surface color in the visual cortex, while the figure-ground effect results from two mechanisms of border ownership assignment, one that is sensitive to asymmetric shape of edge profile, the other to consistency of color borders.

The organization of shape and color in vision and art

“…Under these conditions, the border ownership is weakened and the figure–ground segregation appears reversible. This result suggest that figure–ground and depth segregation are independent from the coloration effect (Pinna, 2005; Pinna and Reeves, 2006; von der Heydt and Pierson, 2006). Pinna (2005) and Pinna and Reeves (2006) introduced the “asymmetric luminance contrast principle” (Pinna, 2005) stating that, all else being equal, given an asymmetric luminance contrast on both sides of a contour, the region, whose luminance gradient is less abrupt, is perceived as a figure if compared to the complementary more abrupt region perceived as a background.…”

“…Furthermore, Zhou et al (2000) reported that approximately half of the neurons in the early cortical areas are selective in coding the polarity of color contrast. The same correlate can be assumed to explain the figure–ground effect of the watercolor illusion (von der Heydt and Pierson, 2006). The specialized phenomenal roles of the juxtaposed and displaced contours in boundary and color and the phenomenal logic of their organization can shed light to understand how neurons become more and more specialized by firing to only one attribute and how they are then integrated, after a level of juxtaposition of attributes.…”

“…Given that a single contour is perceived like the boundary of an object and appears to impart a surface color/brightness attribute, it follows that the information about shape and color is placed on the contour. This is clearly demonstrated by the watercolor illusion (Pinna, 1987, 2005, 2008; Pinna et al, 2001, 2003; Wollschläger et al, 2002; Spillmann et al, 2004; Devinck et al, 2005; Pinna and Grossberg, 2005; von der Heydt and Pierson, 2006; Werner et al, 2007). The illusion (see Figure 5), induced by two juxtaposed contours of different colors and luminance contrast, strongly increases the unilateral belongingness of the boundaries and the surface coloration through a long range color spreading (see Pinna, 2010a).…”

Simultaneous Brightness and Apparent Depth from True Colors on Grey: Chevreul Revisited

“…Given that such induction effects often occur together with changes in the perceived depth of either the inducing field or the test field, as in the watercolor illusion (e.g. Pinna and Reeves, 2006;von der Heydt and Pierson, 2006), we compared probabilities of simultaneous induction with the probabilities that the patterns which generate them are seen as nearer to the observer. In fact, inducers with a stronger tendency to be perceived as separated in depth from their immediate backgrounds may also have a stronger tendency to produce induction effects in terms of apparent contrast.…”

Perceptual Organization of Shape, Color, Shade, and Lighting in Visual and Pictorial Objects

“…To answer these questions, we suggest introducing along the contours some variations as demonstrated by the watercolor illusion (Devinck et al 2005; Pinna 1987, 2005, 2008b; Pinna and Grossberg 2005; Pinna et al 2001; Pinna et al 2003; Spillmann et al 2004; von der Heydt and Pierson 2006; Werner et al 2007; Wollschläger et al 2002). The set of figural properties emerging from this illusion depends on two factors: the juxtaposition of contours and the formation of asymmetrical luminance and chromatic conditions along the contours.…”