Innateness of colour categories is a red herring: insights from computational modelling

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

2. 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)

3. 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)

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

5. 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)

6. 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.

7. 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)

8. 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.

9. 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)

10. 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.

11. 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.

12. 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.

13. Chromatic data • Three data sets: natural, urban and random

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

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

16. 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.

17. 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.

18. 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!

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

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

21. 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.

22. 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 http://arti.vub.ac.beSteels & Belpaeme (2005) Coordinating Perceptually Grounded Categories through Language: A Case Study for Colour. Behavioral and Brain Sciences. To appear.