08. Color illusion biases perception of foreground

Abstract

The watercolor illusion (WCI), sometimes referred to as the water-color effect, is a visual illusion in which physically white space appears to be a less saturated hue of a physically colored contrast edge (Hale & Brown, 2018). In this experiment, we used images of abstract shapes to examine the extent to which this illusion could bias a particular region toward foreground (i.e. the region looks like a figure or object) or background. Images consisted of a centrally located square with a dark wavy line dividing it into two parts. There were three conditions: no WCI, WCI only on the left side of the wavy line, and WCI only on the right. Therefore, either the right or left part of the square contained illusory color for the two WCI conditions. Thirty participants were asked to indicate which side of each image appeared to be the foreground. We predicted participants would perceive the WCI-containing region as figure more often since the WCI is a strong cue for figure-ground (e.g. Pinna & Grossberg, 2005). Participants saw the left and right of the control condition as figure statistically half the time indicating no figure-ground bias for the control. In the WCI conditions, participants reported seeing the WCI-containing region as figure statistically more often than the non-WCI-containing region when it was on the left, t(30) = -7.084, p < .001, or on the right, t(30) = 6.462, p < .001. This study further supports the strong figural biasing nature of the WCI.