Friday, April 10, 2009

Language and color perception

by Terry Regier, University of Chicago and Paul Kay, University of California at Berkeley

[At the 2007 IS&T/SID Color Imaging Conference, Terry Regier gave a keynote address on how color discrimination is influenced by linguistic categories in the right but not in the left visual field. Now he revisits the topic with noted color/language expert Paul Kay. While reading, you might contemplate, how do I try this at home? - MHB ]

Does language affect perception, or not? The yes-or-no framing of this question obscures an interesting possibility. Several recent studies on color suggest that language does indeed affect perception (or at least perceptual discrimination) – but it does so primarily in the right visual field (RVF), and much less if at all in the left visual field (LVF), a pattern suggested by the functional organization of the brain. Thus, half of our perceptual world is viewed through our native language, and half is viewed without a linguistic filter.

This pattern was first shown in a study [1] that probed the discrimination of colors straddling the boundary between green and blue, a boundary present in English but absent in many other languages. The study found evidence for categorical perception of color – faster discrimination of colors from different categories – but only in the RVF, not in the LVF. This lateralization was disrupted by a concurrent task that interfered with verbal processing, but not by a concurrent task of comparable difficulty that interfered only with non-verbal processing – suggesting that the pattern is verbal in origin. Other studies replicated and extended this finding, exploring the cross-cultural and developmental origins of our tendency to view half of our visual world through language, and half of it less so if at all.

If color categories affect perception, at least in half the visual field, where do those categories come from? Why do languages have the color categories they do? An influential universalist view of color naming holds that color categories across languages are organized around the universal focal colors black, white, red, green, yellow, and blue. A recent relativist challenge holds in contrast that there are no such universal foci, and that color categories are defined at their boundaries by largely arbitrary linguistic convention. Both of these views are partly supported and partly challenged by existing data, which show universal tendencies in color naming, coupled with interesting cross-language variation of category boundaries.

This complex picture can be accounted for starting with the observation that perceptual color space is irregular, in the sense that the maximum possible saturation varies unevenly across hue/lightness combinations. One proposal [2] is that color naming reflects optimal or near-optimal partitions of this irregular space. Recently, this idea was formalized and tested against empirical data [3]. A well-formedness measure was defined that captures the extent to which a given categorical partition of color space maximizes perceptual similarity within color categories and minimizes it across categories. Across the 110 languages of the World Color Survey – a database of color naming from non-industrialized societies worldwide – color naming tended to be near-optimal in well-formedness. At the same time, linguistic convention may get some wiggle room: Often, similar but different partitions are roughly equally well-formed, suggesting a middle ground between “nature” and “nurture” in color naming across languages.

Neither of these findings – that language affects color perception primarily in the right visual field, or that color naming is near-optimal – is anticipated by the traditional universalist-versus-relativist debate over language and perception. Instead, these findings suggest novel perspectives on the relation of language and perception.

[1] A. Gilbert et al. (2006). Whorf hypothesis is supported in the right visual field but not the left. PNAS 103, 489-494.
[2] K. Jameson & R. D’Andrade (1997). “It’s not really red, green, yellow and blue: an inquiry into perceptual color space,” in Color Categories in Thought and Language, C. L. Hardin and L. Maffi (eds.), Cambridge University Press, 295-319.
[3] T. Regier et al. (2007). Color naming reflects optimal partitions of color space. PNAS 104, 1436-1441.