Slow updating of the achromatic point after a change in illumination

Abstract

For a color constant observer, the color appearance of a surface is independent of the spectral composition of the light illuminating it. We ask how rapidly color appearance judgments are updated following a change in illumination. We obtained repeated binary color classifications for a set of stimuli defined by their reflectance functions and rendered under either sunlight or skylight. We used these classifications to derive boundaries in color space that identify the observer's achromatic point. In steady-state conditions of illumination, the achromatic point lay close to the illuminant chromaticity. In our experiment, the illuminant changed abruptly every 21 s (at the onset of every 10th trial), allowing us to track changes in the achromatic point that were caused by the cycle of illuminant changes. In one condition, the test reflectance was embedded in a spatial pattern of reflectance samples under consistent illumination. The achromatic point migrated across color space between the chromaticities of the steady-state achromatic points. This update took several trials rather than being immediate. To identify the factors that governed perceptual updating of appearance judgments, we used two further conditions, one in which the test reflectance was presented in isolation and one in which the surrounding reflectances were rendered under an inconsistent and unchanging illumination. Achromatic settings were not well predicted by the information available from scenes at a single time point. Instead, the achromatic points showed a strong dependence on the history of chromatic samples. The strength of this dependence differed between observers and was modulated by the spatial context.

What is white?

“…To return to the question of what it is that underlies perception of white, it is clear from our results and those of many others (Helson & Michels, 1948;Honjyo & Nonaka, 1970;Hurvich & Jameson, 1951;Jameson & Hurvich, 1951a, 1951bLee, Dawson, & Smithson, 2012;McDermott & Webster, 2012;Webster & Leonard, 2008;Werner & Schefrin, 1993;Werner & Walraven, 1982) that white is not a single chromaticity. Different observers and even the same observer on different occasions can perceive a surprisingly large range of chromaticities as white, with this range about 2.5 times greater in the blueyellow direction than in the red-green direction.…”

The achromatic locus: Effect of navigation direction in color space

“…The idea that the chromatic system is at a ''resting state'' at the achromatic locus has led to the use of the achromatic point as a means to scale the cone fundamentals (Bompas, Powell, & Sumner, 2013;Walraven & Werner, 1991). Experimentally, settings of the achromatic loci are widely used to establish the effect of illumination or to assess spatial or temporal context effects (see, e.g., Doerschner, Boyaci, & Maloney, 2004;Lee, Dawson, & Smithson, 2012). The extent of invariance of these achromatic settings depends on the spatial configuration, the chromaticity Citation: Chauhan, T., Perales, E., Xiao, K., Hird, E., Karatzas, D., & Wuerger, S. (2014).…”

Context-dependent judgments of color that might allow color constancy in scenes with multiple regions of illumination

“…Ten additional stimuli, randomly chosen from those in the session, were presented at the start of the session. In a previous study, we showed that, after a change in illumination conditions, color classification reaches steady-state levels within approximately ten 2 s trials [27]. The responses to these ten additional presentations were discarded.…”

“…If the time constants of temporal adaptation were sufficiently long, spatially localized mechanisms might be made to extract a spatial average if eye movements sampled sufficient spatial locations [26]. Indeed, we have shown that, with limited eye movements, the temporal sequence of chromaticities is equally as effective in determining color appearance as the spatial array of chromaticities [27,28]. To first approximation, temporal adaptation is set by the mean chromaticity of the sequence of chromatic samples to which the observer is exposed, at least over a time course of tens of seconds [12].…”