Dissecting the influence of the collinear and flanking bars in White’s effect

Abstract

In White’s effect equiluminant test patches placed on the black and white bars of a square-wave grating appear different in brightness. The illusion has generated intense interest because the direction of the brightness effect does not correlate with the amount of black or white border in contact with the test patch, or in its general vicinity. Therefore, unlike brightness induction effects such as simultaneous contrast, White’s effect is not consistent with explanations based on contrast or assimilation that depend solely on the relative amounts of black and white surrounding the test patches. We independently manipulated the luminance of the collinear and flanking bars to investigate their influence on test patch matching luminance (brightness). The inducing grating was a 0.5 c/d square-wave and test patches measured 1.0° in width and either 0.5° or 3.0° in height. Test patches measuring 0.5° in height had more extensive contact with the collinear bars and test patches measuring 3.0° in height had more extensive contact with the flanking bars. The luminance of the collinear (or flanking) bars assumed twenty values from 3.2 to 124.8 cd/m2, while the luminance of the flanking (or collinear) bars remained white (124.8 cd/m2) or black (3.2 cd/m2). Under these conditions the influence of the collinear and flanking bars was found to be purely in the direction of contrast. The effect was dominated by contrast from the collinear bars (which results in White’s effect), however, the influence of the flanking bars was also in the contrast direction. The data elucidate the luminance relationships between the collinear and flanking bars which produce the behavior associated with White’s effect as well as that associated with “the inverted White effect” which is akin to simultaneous contrast.

What Fechner could not do: Separating perceptual encoding and decoding with difference scaling

“…The targets in white are decrements and their brightness scale similarly crispens near the white collinear bar as well as near the black minimum luminance. This dominant role for the collinear, but not the flanking, contrast in White's (1979) effect has previously been implied (e.g., Betz et al., 2015a ; Betz et al., 2015b ; Blakeslee, Padmanabhan, & McCourt, 2016 ).…”

Urban experience alters lightness perception.

“…One obvious possibility is that the Himba possess uncorrected refractive errors (although previous tests of visual acuity have not supported this). While White’s illusion—like simultaneous lightness contrast—is purely contrast-based at the low spatial frequencies of grating used here (Blakeslee, Padmanabhan, & McCourt, 2016), refractive errors would effectively cause assimilation effects that also affect White’s illusion (Blakeslee & McCourt, 2004). Assimilation effects, however, enhance White’s illusion, suggesting that refractive differences do not play an important causal role here.…”

Isolation of brightness induction effects on target patches from adjacent surrounds and remote backgrounds

“…The oriented filter explanation for the White effect is further supported by a more recent study (Blakeslee et al, 2016 ) in which the luminance of the collinear and flanking bars was independently manipulated in order to investigate their separate influence on target patch matching luminance (apparent intensity or brightness). The inducing grating was a 0.5 c/d square-wave and target patches measured 1.0° in width and either 0.5° or 3.0° in height.…”

“…Optical blurring does not obviate the need for a neural explanation of the effect as well, however, since the signature of optical blurring (a linear increase in magnitude as a function of inducing luminance), is not always observed (Jameson and Hurvich, 1989;Hong and Shevell, 2004). In other instances (discussed in detail below), effects that are described as brightness assimilation have been shown to result from strong directional brightness contrast mechanisms (Blakeslee et al, 2016); while others, which are the topic of the present article, appear to be the manifestation of remote brightness contrast mechanisms (Shapley and Reid, 1985;Reid and Shapley, 1988).…”