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Journée(s) d'étude

10h00 – 12h30

Jules Davidoff (Centre for Cognition, Computation and Culture, Goldsmiths, University of London)

Are colour categories universal?

The question of whether language affects our categorisation of perceptual continua is of particular interest for the domains of colour and shape where constraints on categorisation have been proposed both within the visual system and in the visual environment. Our initial research in New Guinea (Davidoff et al, 1999; Roberson et al, 2000) found substantial evidence of cognitive colour differences between different language communities, but concerns remained as to how representative might be a tiny, extremely remote community. That study has now been replicated (Roberson et al, 2004, 2005) extending previous findings with additional paradigms among a larger community in a different visual environment. Adult semi-nomadic Himba tribesmen in Namibia, also with a 5 term colour language, carried out similarity judgments, short-term memory and long-term learning tasks. They showed different cognitive organisation of colour to both English and the New Guinea language.
A group of Himba children was compared over a three-year period to a group of English children on colour naming and comprehension, together with the ability to remember colours. Despite large differences in visual environment, language and education, children from both cultures appeared to acquire colour vocabulary slowly and with great individual variation. The influence of naming on memory increased over time for both groups of children. Thus, longitudinal studies confirmed the role of colour labels in the acquisition of colour categories both in Himba and English. These results provide further evidence of the tight relationship between language and cognition.
As the visual system does not provide adequate neurophysiological discontinuities to give natural colour category boundaries, and our recent evidence points to a linguistic origin, baboons and humans were given the same task of matching to sample colours that crossed the green/blue boundary. The data and consequent modelling were remarkably clear-cut (Fagot et al, in press). All human participants matched our generalisation probe stimuli as if to a sharp boundary close to the midpoint between their training items. Despite good colour discrimination, none of the baboons showed any inclination to match to a single boundary but rather responded with two boundaries close to the training stimuli. These data, along with the cross-lingual studies give no support to the claim that colour categories are explicitly instantiated in the primate colour vision system.
Quelques références:

Davidoff, J., Davies, I.R.L., & Roberson (1999). Is colour categorisation universal? New evidence from a
stone-age culture. Nature, 398, 203-204.

Fagot, J. Goldstein, J., Davidoff, J. & Pickering, A. (in press) Cross-species differences in color categorization. Psychonomic Bulletin & Review.

Roberson, D., Davidoff, J, Davies, I. & Shapiro, L. (2005). Color categories: evidence for the relativity hypothesis. Cognitive Psychology, 50, 378-411.

Roberson, D., Davidoff, J, Davies, I. & Shapiro, L. (2004). The development of color categories in
two languages: a longitudinal study. Journal of Experimental Psychology: General, 133, 554-571.

Roberson, D., Davies, I. & Davidoff, J. (2000) Color categories are not universal: Replications and new
evidence from a stone-age culture. Journal of Experimental Psychology: General, 129, 369-398.

14h00-15h30

L'approche sensorimotrice des sensations se distingue de l'approche classique en postulant qu'une sensation n'est pas le produit final d'un processus de traitement de l'information dans le cerveau, mais est au contraire constituée par une habileté sensorimotrice exploratoire dans laquelle l'organisme entier est engagée. Cette conception, plus intuitive pour les sensations tactiles, paraît plus difficile à entretenir pour la couleur, car la couleur semble a priori impliquer aucune activité exploratrice. Néanmoins, comme prédit par l'approche sensorimotrice, des résultats d'expériences d'adaptation montrent que la sensation de couleur peut être modulée par l'association systématique avec des mouvements des yeux.

15h45-17h30

D. Philipona & J. K. O'Regan (Laboratoire de Psychologie Expérimentale, CNRS, Université René Descartes Paris 5)

Une approche biologique des propriétés de réfléchissement des surfaces prédit la catégorisation linguistique des couleurs et l'identité des couleurs uniques.

One of the most basic aspects of color vision, namely the special role of the colors red, green, blue and yellow, is usually assumed to have a purely neuronal cause. We will show a fact that suggests a fundamentally different origin: from the viewpoint of human photopigments, red, green, blue and yellow surfaces alter light in a simpler way than all other surfaces. This is demonstrated by constructing a biological restriction of the physicist's notion of reflectance that takes into account the statistical constraints satisfied by natural illuminants and the limitations induced by human photopigments. Using a dataset of natural and artificial reflectances, we then show numerically that the existence and the identity of four singular hues is actually to be expected from trichromatic theory alone, independently of any opponent mechanisms. This approach very directly provides correct quantitative predictions for psychophysical data about unique hues, hue cancellation, and cross-cultural data about color naming.