Spatial Dependence of Color Assimilation by the Watercolor Effect

Abstract

Color assimilation with bichromatic contours was quantified for spatial extents ranging from von Bezold-type color assimilation to the watercolor effect. The magnitude and direction of assimilative hue change was measured as a function of the width of a rectangular stimulus. Assimilation was quantified by hue cancellation. Large hue shifts were required to null the color of stimuli ≤ 9.3 min of arc in width, with an exponential decrease for stimuli increasing up to 7.4 deg. When stimuli were viewed through an achromatizing lens, the magnitude of the assimilation effect was reduced for narrow stimuli, but not for wide ones. These results demonstrate that chromatic aberration may account, in part, for color assimilation over small, but not large, surface areas.

Illusory spreading of watercolor

“…The WCE appears to involve different mechanisms at a different level of processing than are needed to explain previously described color assimilation effects. Although larger color assimilation effects are seen with decreasing distance between the inner components of the inducing contours in the WCE, assimilation is still seen in relatively large patterns in which the assimilated area is much larger than would be expected from classical accounts of contrast versus assimilation (Devinck et al, 2006;Pinna et al, 2001). Consequently, classical receptive field organization does not fully explain the WCE.…”

“…Assimilation effects are most often observed in displays containing high spatial frequency patterns (Helson, 1963;Smith, Jin, & Pokorny, 2001); however, other factors such as the width of the inducing contour (Fach & Sharpe, 1986) or the luminance relationships within the stimulus can also influence whether assimilation is observed (Cao & Shevell, 2005;De Weert & Spillmann, 1995;Hamburger, 2005;Helson, 1963;Wook Hong & Shevell, 2004). As with other assimilation patterns, the strength of the WCE decreases with increasing edge width (Pinna et al, 2001) and induced area (Devinck, Delahunt, Hardy, Spillmann, & Werner, 2006) or increases with the luminance contrast between the two double contours (Devinck, Delahunt, Hardy, Spillmann, & Werner, 2005). These variables are also known to influence the strength of color contrast tested under a wide range of conditions (Krauskopf, Zaidi, & Mandler, 1986;Ware & Cowan, 1982;Zaidi, Yoshimi, Flanigan, & Canova, 1992).…”

Spatial selectivity of the watercolor effect

“…A temporal presentation was ruled out to avoid the possibility of memory effects. Free viewing has been used to study the WCE in numerous previous studies [1][2][3]6,7,16,17]. Two previous studies have used durations, respectively, of 1 s [10], not too much shorter than our estimated average duration, and 150 ms to study an achromatic variant of the WCE [4].…”

“…For example, increasing the luminance contrast between the inner and outer contours leads to a stronger saturation of the fill-in color [3][4][5]. Also, larger chromatic contrasts between the contour pairs leads to a stronger effect [2,6]. Although the WCE has been reported for straight contours [2,7], its strength has been demonstrated to depend on the frequency and amplitude of the contour undulation [8].…”

Contributions of contour frequency, amplitude, and luminance to the watercolor effect estimated by conjoint measurement

“…The strength of the WCE is influenced by several factors, including the relative luminances of the contours (Devinck, Delahunt, Hardy, Spillmann, & Werner, 2006;Devinck & Knoblauch, 2012), the width of the inducing contours (Pinna et al, 2001;Devinck, Gerardin, Dojat, & Knoblauch, 2014), and the continuity and contiguity of the contour pairs (Devinck & Spillmann, 2009). Most studies have assessed the strength of the effect with matching or hue cancellation Citation: Gerardin, P., Devinck, F., Dojat, M., & Knoblauch, K. (2014).…”