What the Optics of the Aging Eye Can Teach Us About Color Language

Many languages without separate terms for green and blue are or were spoken in locations receiving above-average exposure to ultraviolet-B (UV-B) radiation. It has been proposed that this correlation is caused by premature lens aging. This conclusion was supported by an experiment in which younger observers used the term ‘‘blue’’ less often when they described simulated paint chips filtered through the equivalent of an older observer’s lens—removing much short-wavelength light—than when they described the unfiltered versions of the same paint chips. Some stimuli that were called ‘‘blue’’ without simulated aging were called ‘‘green’’ when filtered. However, in the experiment reported here, we found that the proportion of ‘‘blue’’ color-name responses did not differ between younger subjects and older observers with known ocular media optical densities. Color naming for stimuli that were nominally green, blue-green, or blue was virtually identical for older and younger observers who viewed the same (unfiltered) stimuli. Our results are inconsistent with the lens-brunescence hypothesis. Most humans can discriminate millions of colors, yet in every language studied systematically, the number of basic color terms (BCTs) is comparatively small. In English, for example, there are 11 BCTs, that is, black, white, red, yellow, green, blue, purple, brown, orange, pink, and gray (Berlin & Kay, 1969). BCTs refer to the smallest collection of simple words with which a speaker can name any color. A few languages have more than 11 BCTs— Russian has distinct BCTs for light blue and dark blue, Hungarian for light red and dark red—but many languages have fewer. Welsh and most other Celtic languages, for example, do not have distinct BCTs for green and blue (Lazar-Meyn, 2004), and the same is true for almost all unwritten languages. The set of color terms within a language is not random. Rather, there is a distinct tendency for languages to evolve color terms in a particular order. For example, no language is known to have distinct words for blue and green and yet fail to distinguish red and yellow. The origins and mechanisms underlying the regularity of color naming across languages have been topics of considerable investigation (e.g., Heider, 1972; Kay & Maffi, 1999; Kay & McDaniel, 1978) and debate (e.g., Davidoff, Davies, & Roberson, 1999; Hickerson, 1971; Lucy, 1997). Recently, Lindsey and Brown (2002) have offered an interesting hypothesis to explain why some languages lack BCTs that distinguish green and blue. According to their argument, most so-called grue languages (those with a single term covering both green and blue) occur in geographic locations closer to the equator or at higher elevations than the locations of languages that have separate terms for green and blue. Thus, speakers of grue languages tend to receive above-average levels of ultraviolet-B (UV-B) radiation from the sun. High UV-B exposure is linked to accelerated ocular media aging, most particularly of the crystalline lens (Javitt & Taylor, 1994–1995; Werner, Peterzell, & Scheetz, 1990; Young, 1991). As the crystalline lens ages, a process known as brunescence occurs. The lens becomes denser and more opaque, allowing less light, especially at shorter wavelengths, to reach the retina (Weale, 1988). Individuals experiencing premature lens aging would receive less short-wavelength light at the retina when viewing the same Address correspondence to Joseph L. Hardy, Department of Ophthalmology, 4860 Y St., Suite 2400, Sacramento, CA 95817; e-mail: joe.hardy@positscience.com. PSYCHOLOGICAL SCIENCE Volume 16—Number 4 321 Copyright r 2005 American Psychological Society stimuli as people with more transparent lenses. Lindsey and Brown argued that this reduced exposure to short-wavelength light would reduce the need for the color term ‘‘blue,’’ usually assigned to stimuli predominantly composed of energy at shorter visible wavelengths. Thus, they proposed that languages spoken by cultures located in high-UV-B areas would tend to be grue languages. To test this hypothesis, Lindsey and Brown (2002) performed a color-naming experiment in which they simulated the effects of lens brunescence in young individuals. This simulation took advantage of the lens-aging model of Pokorny, Smith, and Lutze (1987) to transform stimulus chromaticities to simulate the effects of optical aging. Young observers were shown simulated Munsell chips (a set of color standards) made yellower and darker in the exact proportions prescribed by the Pokorny et al. lens model to simulate the effects of age-related lens opacity changes of individuals ages 50 to 100. As predicted by Lindsey and Brown’s lens-brunescence hypothesis, observers used the term ‘‘blue’’ progressively less often as the simulated lens was increasingly aged. Chips previously called ‘‘blue’’ were called ‘‘green’’ or ‘‘gray’’ after being transformed by simulated aging. Lindsey and Brown concluded that the results of this experiment show that premature lens brunescence could lead to a reduced need for the term ‘‘blue. ’’ This argument has created considerable interest and some controversy (e.g., Lazar-Meyn, 2004; Lindsey & Brown, 2004; Regier & Kay, 2004). Although Lindsey and Brown’s (2002) aging simulation was mathematically consistent with a valid model of lens brunescence, the effects of lens aging can be tested more directly by testing individuals of various chronological ages and, thus, a range of ocular media optical densities (ODs). The results of this more direct test could differ from the results of a simulation. Younger observers viewing stimuli designed to simulate the optics of the aging eye experience lower light levels and higher proportions of long-wavelength light for a matter of minutes. Older individuals with brunescent lenses live with their optics continuously, as do people with more brunescent lenses as a result of living in high-UV-B areas. Although Lindsey and Brown did have observers briefly (3 min) adapt to the background color prior to the experiment, chromatic adaptation can operate on very long time scales, on the order of days (Neitz, Carroll, Yamauchi, Neitz, & Williams, 2002) or even months (Delahunt,Webster, Ma, &Werner, 2004). Chromatic adaptation has the effect of changing how the visual system interprets the light reaching each of the three photoreceptor types (Jameson & Hurvich, 1956; Uchikawa, Uchikawa, & Boynton, 1989). Longterm chromatic adaptation could largely compensate for changes in the average spectral distribution of light reaching the retina due to age-related changes in the lens. Thus, although such a simulation can closely replicate the patterns of wavelengths reaching the retina in observers with differing ocular media ODs, it is unlikely to accurately simulate the perceptual experience of observers with naturally brunescent lenses. To test Lindsey and Brown’s (2002) lens-brunescence hypothesis, we compared color naming in individuals with a range of known ocular media ODs. We did this in two ways. In one set of conditions, we tested color naming in groups of younger and older observers with the same standard stimulus set used by Lindsey and Brown. In a separate set of conditions, we tested color naming in each of these groups using stimuli that simulated the effects of ocular media present in the complementary age group (i.e., younger observers viewed stimuli filtered through the simulated ocular media of older observers, and older observers viewed stimuli filtered through the simulated ocular media of younger observers). If Lindsey and Brown’s (2002) proposal is correct, color naming by older observers in the standard condition would be expected to be similar to color naming by younger observers in the simulated-aging condition. Also, color naming by younger observers in the standard condition would be expected to be similar to color naming by older observers in the simulated‘‘youthening’’ condition. Specifically, stimuli denoted in the Munsell color system as ‘‘blue-green’’ and ‘‘blue’’ would be expected to be identified with the color name green more often by older subjects viewing standard stimuli and younger subjects viewing simulated-aging stimuli than by younger subjects viewing standard stimuli and older subjects in the simulatedyouthening condition. Additionally, in the standard stimulus conditions, a strong negative correlation between ocular media OD and use of the color term blue would be expected. Evidence from studies examining the effects of aging on unique hue loci (Schefrin & Werner, 1990), hue scaling (Schefrin & Werner, 1993), and color naming in Japanese (Okajima, Yamashita, Takamura, Watanabe, & Tsuchiya, 2002), however, casts doubt on these predictions. These studies show that older observers, despite their increased ocular media OD, tend to use linguistic color descriptors in much the same way as younger observers. This suggests that when older observers and younger observers are presented with the same stimuli, their color naming should be similar.