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What #Thedress Reveals About the Role of Illumination Priors in Color Perception and Color Constancy

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What #Thedress Reveals About the Role of Illumination Priors in Color Perception and Color Constancy Aston S, Hurlbert A. What #theDress reveals about the role of illumination priors in color perception and color constancy. Journal of Vision 2017, 17(9). Copyright: © 2017 The Authors This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. DOI link to article: http://doi.org/10.1167/17.9.4 Date deposited: 07/11/2017 This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International licence Newcastle University ePrints - eprint.ncl.ac.uk Journal of Vision (2017) 17(9):4, 1–18 1 What #theDress reveals about the role of illumination priors in color perception and color constancy Institute of Neuroscience, Newcastle University, # Stacey Aston Newcastle upon Tyne, UK $ Institute of Neuroscience, Newcastle University, # Anya Hurlbert Newcastle upon Tyne, UK $ The disagreement between people who named #theDress media in February 2015; Figure 1) ‘‘blue and black’’ (the Internet phenomenon of 2015) ‘‘blue and black’’ versus ‘‘white and gold’’ illustrates the subjectivity and versus ‘‘white and gold’’ is thought to be caused by individuality of color perception. While there are individual differences in color constancy. It is many examples of illusions in which an individual hypothesized that observers infer different incident observer sees a colored object differently in different illuminations, relying on illumination ‘‘priors’’ to viewing conditions (e.g., color contrast and color overcome the ambiguity of the image. Different assimilation; Brainard & Hurlbert, 2015), #theDress experiences may drive the formation of different phenomenon differs from these in eliciting striking illumination priors, and these may be indicated by differences in chronotype. We assess this hypothesis, inter-individual differences under identical viewing asking whether matches to perceived illumination in the conditions. image and/or perceived dress colors relate to scores on When #theDress first appeared people immediately the morningness-eveningness questionnaire (a measure fell into two groups: one group reported a blue dress of chronotype). We find moderate correlations between with black lace and the opposing group saw a white chronotype and illumination matches (morning types dress with gold lace. As controlled studies have since giving bluer illumination matches than evening types) and shown, these naming differences are not due to chronotype and dress body matches, but these are different viewing devices (Gegenfurtner, Bloj, & To- significant only at the 10% level. Further, although scani, 2015; Lafer-Sousa, Hermann, & Conway, 2015). inferred illumination chromaticity in the image explains In addition, the stark division of people into only two variation in the color matches to the dress (confirming the naming groups seems to have occurred only due to the color constancy hypothesis), color constancy thresholds way the question was posed on social media. When obtained using an established illumination discrimination participants were allowed to free-name the colors of the task are not related to dress color perception. We also dress, a continuum of color names emerged, but with find achromatic settings depend on luminance, suggesting three modal groups: blue and black (B/K), white and that subjective white point differences may explain the gold (W/G), and blue and gold (B/G; Lafer-Sousa et variation in dress color perception only if settings are al., 2015). made at individually tailored luminance levels. The results of such achromatic settings are inconsistent with their Previous studies have also shown that observers assumed correspondence to perceived illumination. differ not only in how they name the dress but also in Finally, our results suggest that perception and naming the colors to which they match it (Chetverikov & are disconnected, with observers reporting different color Ivanchei, 2016; Gegenfurtner et al., 2015; Lafer-Sousa names for the dress photograph and their isolated color et al., 2015), leading to the conclusion that the matches, the latter best capturing the variation in the phenomenon is a perceptual one and therefore not matches. explained solely by differences in color naming and/or color categorization. However, previous studies differ somewhat in their matching results. In one study, where 53 laboratory participants made matches to the Introduction dress body and lace using a color picker tool, matches to both regions differed between B/K and W/G The division between people who named #theDress observers in both lightness and chromaticity (Lafer- (the dress photograph that first appeared on social Sousa et al., 2015). In another, Gegenfurtner et al. Citation: Aston, S., & Hurlbert, A. (2017). What #theDress reveals about the role of illumination priors in color perception and color constancy. Journal of Vision, 17(9):4, 1–18, doi:10.1167/17.9.4. doi: 10.1167/17.9.4 Received January 10, 2017; published August 9, 2017 ISSN 1534-7362 Copyright 2017 The Authors This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. Downloaded From: http://jov.arvojournals.org/pdfaccess.ashx?url=/data/journals/jov/936403/ on 11/07/2017 Journal of Vision (2017) 17(9):4, 1–18 Aston & Hurlbert 2 light (see figure 2 in Brainard & Hurlbert, 2015). If a difference in inferred illumination is responsible for the difference in perception then we must ask, what causes different observers to infer different illumina- tions? It might be that observers rely on previous experience—unconsciously embedded in the percep- tual process—to determine the most likely illumina- tion and overcome the uncertainty in the visual information. In the Bayesian framework for visual perception, the knowledge learned from previous visual experience is incorporated as prior probability distributions on thestimulusspace,or‘‘priors.’’UndertheBayesian brain hypothesis, it is assumed that the visual system Figure 1. The photo of the dress taken from Wikipedia. uses priors to weight the uncertainty of sensory Photograph of the dress used with permission. Copyright Cecilia signals, effectively biasing perception towards the Bleasdale. observer’s internal expectations based on prior expe- rience with stimuli (Allred, 2012; Brainard & Free- (2015) asked participants to make color matches to man, 1997; Kersten & Yuille, 2003; Sotiropoulos & both the dress body and lace as well as to select the Serie`s, 2015). For example, internal priors may bias best matching chip from the glossy version of the strawberry shapes to be red, or more relevant to the Munsell Book of Colour. Contrary to the results of current study, daylight illuminations to vary from blue Lafer-Sousa et al. (2015), both sets of matching data to yellow. Although there is evidence for the contri- did not differ in chromaticity between the two groups bution of prior knowledge to color perception (Allred, of observers but did differ in luminance (or value in 2012; Hansen, Olkkonen, Walter, & Gegenfurtner, the case of the Munsell chips). A later online survey 2006), there is a lack of evidence for illumination found differences in the matches for the B/K and W/G priors per se. Previous work has shown that the observer groups along all axes of CIELAB color space human visual system displays a robust color constancy (Chetverikov & Ivanchei, 2016). It is clear from these bias for bluer daylight illumination changes, with results that representing an individual’s perception of observers finding it harder to discriminate an illumi- the photograph only by the color names they assign is nation change on the scene if the illumination becomes not enough to capture the variability in perception bluer rather than yellower, redder, or greener (Pearce, across the population. Clearly, there are substantial Crichton, Mackiewicz, Finlayson, & Hurlbert, 2014; individual differences in the processes of color Radonjic, Pearce et al., 2016). It is unresolved whether perception that are responsible for the phenomenon, this reduced sensitivity to bluer illumination changes but the detailed characteristics of these underlying is a top-down influence on visual perception, as priors factors remains somewhat elusive. are generally considered to be, or whether the lack of Brainard and Hurlbert (2015) suggested the color sensitivity to these changes has become embedded in constancy hypothesis to account for the differences. bottom-up visual processing through development Color constancy is the phenomenon by which the and/or evolution. In either case, it is possible that perceived colors of objects remain stable despite individual differences in illumination estimation or changes in the incident illumination (Hurlbert, 2007; illumination change discrimination may be due to for review see Foster, 2011, or Smithson, 2005). The differences in experience. If two individuals experience perceptual mechanisms underlying color constancy different occurrence distributions of illumination are generally thought to involve an unconscious spectra, leading to the formation of different illumi- inference about the incident illumination, which is nation priors, or to their visual systems adapting to then discounted to enable the recovery of constant become insensitive to these changes, the consequence surface properties. The color constancy hypothesis for in either case will be a difference in immediate #theDress phenomenon implies that individual differ- perception. ences in perception of the photograph arise because
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