Innateness of colour categories is a red herring: insights from computational modelling Tony Belpaeme Artificial Intelligence Lab Vrije Universiteit Brussel

Colour categories The colour spectrum is continuous Still, we divide it into colour categories What are the origins of colour categories? (Insights might be applicable to other perceptual categories as well)

Importance for language “… this may at first appear to be a comparatively trivial example of some minor aspect of language, but the implications for other aspects of language evolution are truly staggering.” (Deacon, 1997)

Universalism Berlin and Kay (1969) used naming experiments to extract colour categories

Universalism This universal character has been hailed by many and has been reconfirmed by some. (among others Rosch-Heider, 1972; Kay and McDaniel, 1978; Durham, 1991; Shepard, 1992; Kay and Regier, 2003)

Three positions Supposing we accept a certain universality of colour categorisation, what mechanisms could underlie this? –Nativism: genetic makeup. –Empiricism: interaction with the environment. –Culturalism: cultural interaction with others.

Nativism Colour categories are directly or indirectly genetically specified. –Regularities in human early visual perception, especially the opponent character of colour vision. (Kay and McDaniel, 1978) –Regularities in the neural coding of the brain. (Durham, 1991) –Genetic coding of colour categories. (Shepard, 1992)

Empiricism Our ecology contains a certain chromatic structure which is reflected in our colour categories. We extract colour categories by interacting with our environment. (e.g. Elman et al., 1996; Shepard, 1992; Yendrikhovskij, 2001) This all happens without the influence of culture or language.

Culturalism Colour categories are culture-specific. They are learned with a strong causal influence of language and propagate in a cultural process. (e.g. Whorf, 1954; Davidoff et al., 2001; Roberson, 2005; Belpaeme and Steels)

Nativism, empiricism or culturalism? The discussion has been held on many different fronts –Neurology. –Psychology. –Anthropology. –Linguistics. –Ophthalmology. –Philosophy. We will tackle the discussion from artificial intelligence and computer modelling.

How can Artificial Intelligence help? Artificial Intelligence allows us to create models of natural phenomena, of which we then observe their behaviour. Different premises can be implemented in the models, allowing us to get an insight into the validity of the premises. –E.g. traffic modelling.

Studying empiricism Procedure –Collect chromatic data. –Extract colour categories. For this we use a clustering algorithm. –Compare extracted categories with each other and with human colour categories. If empiricism holds, we would expect a high correlation between the extracted categories and human categories.

Chromatic data Three data sets: natural, urban and random

Extracting categories Categories from natural data: Categories from urban data:

Quantitative comparison 11 categories extracted from natural and urban data Correlation with human colour categories

Reflections on empiricism The claim that human colour categories are specified by the distribution of chromatic stimuli in the world is not supported by our data. However, there does seem to be a twofold influence by –The structure of the perceptual colour space. –The properties of perceptual categories.

Studying culturalism Procedure –Take a population of simulated individuals that learn colour categories and communicate about colour. If culturalism holds, we expect linguistic interactions to cause sharing of colour categories.

The simulations Agent-based simulations –An agent is a simulated individual, with perception, categorisation, lexicalisation and communication. –Perception maps spectral power distribution onto an internal colour space. –Categorisation maps percepts onto categories, categories have prototypical behaviour. –Lexicalisation connects categories to words. –Communication takes care of uttering word forms. –The agents have no way to access the internal state of other agents: there is no telepathy!

Results Colour categories of two agents Agents arrive at colour categories that are “shared”.

Results (2) Influence of linguistic interactions on categories. But as language is culture-specific, cultural evolution cannot explain universalism.

Summary Empiricism is not a good candidate to explain universalism –There is not enough ecological pressure. Culturalism can explain the sharing of categories in a culture, but not universalism. Nativism can explain universalism, but is to slow to follow ecological changes. –Also, recent neurophysiological and molecular studies point out many differences in colour perception between individuals.

Conclusion A blend of all three positions is needed to explain universalism. But language and culture play a crucial role as the catalysts which binds the perceptual categories of individuals. Read the full story at Steels & Belpaeme (2005) Coordinating Perceptually Grounded Categories through Language: A Case Study for Colour. Behavioral and Brain Sciences. To appear.