Perceived area and the luminosity threshold

Abstract

Observers made forced-choice opaque/luminous responses to targets of varying luminance and varying size presented (1) on the wall of a laboratory, (2) as a disk within an annulus, and (3) embedded within a Mondrian array presented within a vision tunnel. Lightness matches were also made for nearby opaque surfaces. The results show that the threshold luminance value at which a target begins to appear self-luminous increases with its size, defined as perceived size, not retinal size. Moregenerally,the larger the target, the more an increase in its luminance induces graynesslblackness into the surround and the less it induces luminosityinto the target, and viceversa. Correspondingto this luminosity/grayness tradeoff, there appears to be an invariant: Across a wide variety of conditions, a target begins to appear luminous when its luminance is about 1.7times that of a surface that would appear white in the same illumination. These results show that the luminosity threshold behaves like a surface lightness valuethe maximum lightness value, in fact-and is subject to the same laws of anchoring (such as the area rule proposed by Li & Gilchrist, 1999)as surface lightness.

The effects of figure/ground, perceived area, and target saliency on the luminosity threshold

“…All observers reported that they could perceptually organize the trapezoidal target in such a way so that it appeared as a rectangle, but when asked if the target was really a rectangle, they all agreed that it was not. These results are in agreement with those obtained by Bonato and Gilchrist (1999); however, their subjects had other depth cues available to them (stereopsis, accommodation, and convergence), whereas depth information in our displays was provided entirely by pictorial cues-namely, linear perspective and a texture gradient.…”

“…Bonato and Gilchrist (1999) attempted to make a target more groundlike by placing a decrement (darker than its surround) in the target's center. Contrary to the results of the present Experiment 1,their target, which was the background to a square, had a lower luminosity threshold than a homogenous target.…”

The place of white in a world of grays: A double-anchoring theory of lightness perception.

“…Bonato and Gilchrist (1999) showed that a white surround was seen as off-white regardless of the actual luminance of a small incremental square sitting on it (solid triangles in Figure 14). However, the lightness of the same surround was an inverse function of the square's luminance when the incremental target square was much larger (solid circles in Figure 14).…”

“…Shrinking the incremental square (highest local luminance) has two consequences: first, it decreases the weight of the HL step (here, from 1.5 to 1); second, it increases the weight of the surround step (here, from 1 to 17). In the experiment by Bonato and Gilchrist (1999), reflectance matches were made to a separately illuminated Munsell scale on white, where white had a reflectance of 90% and a luminance of 539 cd/m 2 . Therefore, this white on the Munsell scale was the highest peripheral luminance (Lh).…”

“…Considering that the theory itself is still young and unrefined, this seems a sign that we are on a promising track. 7 My original article contains an explicit reference to a similar situation: "In the experiment by Bonato and Gilchrist (1999), reflectance matches were made to a separately illuminated Munsell scale on white, where white had a reflectance of 90% and a luminance of 539 cd/m 2 . Therefore, this white on the Munsell scale was the peripheral highest luminance" (Bressan, 2006b, p. 552).…”