Replicating Color Term Universals through Human Iterated Learning

Replicating Color Term Universals through Human Iterated Learning Jing Xu (jing.xu@berkeley.edu) Thomas L. Griffiths (tom griffiths@berkeley.edu) Department of Psychology, 3210 Tolman Hall Berkeley, CA 94720 USA Mike Dowman (Mike@ImageScope.net) ImageScope Abstract in an attempt to resolve the debate over the universality of color naming. For example, Kay and Regier (2003; Regier, Kay, & Cook, 2005) showed that the focal colors in the WCS data largely fall in similar regions to those seen in English; in another study they defined a statistical measure of “well- formedness”, and used this measure to show that observed systems of color terms correspond to a near-optimal partition of color space (Regier, Kay, & Khetarpal, 2007). The consistent cross-linguistic structure highlighted by the WCS raises a new question: Where do these universals come from? They may be a result of cultural universals that may arise from the homogeneity of biological traits and evolu- tionary paths across cultures that constrain people to consider only a limited range of color categories when learning lan- guage, thus forcing color term systems to conform to a lim- ited range of universal types (Hawkins, 1988). However, if we view language as a system culturally transmitted from generation to generation, a simpler hypothesis is that these universals may arise directly from biases that cause learners to prefer some color categorizations over others, but that do not place absolute constraints on the types of color categories that are learnable. One way to explore this hypothesis is using the iterated learning model, a simple model of cultural trans- mission in which a sequence of agents each learns from the behavior of the previous agent in the sequence (Kirby, 2001). In an iterated learning model of the transmission of systems of color terms, each agent learns a system of color terms from examples provided by another agent, and then generates ex- amples which are provided to the next agent in the sequence. Mathematical analyses of iterated learning show that as this process continues, the information being transmitted gradu- ally changes to become consistent with the learning biases of the agents involved (Griffiths & Kalish, 2007; Kirby, Dow- man, & Griffiths, 2007). If systems of color terms similar to those seen in the WCS emerge from a process of cultural In 1969, Berlin and Kay proposed that there exist cross- cultural universals in the form of basic color terms. To test this hypothesis, the World Color Survey (WCS) collected color naming data from 110 non-industrial societies, identifying reg- ularities in the structure of languages with different numbers of terms. This leaves us with the question of where these uni- versals come from. We use a simple model of cultural evo- lution known as “iterated learning” to explore the hypothesis that universals emerge from human perceptual and learning bi- ases. We conducted an experiment simulating the process of cultural transmission in the laboratory, and compared the re- sults to the systems of color terms that appear in the WCS data. Our results show that cultural evolution results in convergence of systems of color terms towards a form consistent with the WCS, supporting the hypothesis that universals are the result of perceptual and learning biases. Keywords: basic color terms; iterated learning model; color term universals; cultural evolution; Bayesian inference. Introduction Linguistic universals – properties that seem to hold across all human languages – have the potential to provide unique in- sight into the nature of human cognition. Universals in sys- tems of color terms are among the best documented of these properties. Berlin and Kay (1969) proposed that color naming systems across different cultures are based on one or more of eleven focal colors corresponding to the English color terms black, white, red, green, yellow, blue, brown, purple, pink, or- ange, and gray. Kay and McDaniel (1978) and Kay and Maffi (1999) later refined this model to emphasize the six Hering primary colors (black, white, red, green, yellow, and blue) (Hering, 1964), and to characterize the process by which so- cieties might transition from one system of color terms to an- other as new terms are introduced. The World Color Survey (WCS) was initiated in the late 1970’s to provide a more comprehensive empirical test of the univerality hypothesis (Kay, Berlin, & Merrifield, 1991; Kay, Berlin, Maffi, & Merrifield, 1997). In the WCS, a total of 330 color chips, comprised of 40 equally spaced Munsell hues at 8 levels of lightness and achromatic chips at 10 levels of light- ness (see Figure 1), were presented to speakers of 110 dif- ferent languages in non-industrial societies. Those speakers were asked to name each color chip, and also to point out the most representative chip for each color term. Later analysis of the WCS data showed that the universality hypothesis was by and large confirmed (Kay et al., 1997). Recently, several sta- tistical analyses of the WCS data have also been conducted Figure 1: The World Color Survey stimulus array.