Nature recently carried a short piece, Perception coloured by language (written by Kerri Smith), on several research papers, including one by Paul Kay at the University of California, Berkeley (well, actually, Kay is also the co-author on another of the three papers, too). The original article, in the Proceedings of the National Academy of Sciences (US), is not openly accessible, but the abstract is here (Franklin et al. abstract). We’ve had a number of related posts on Neuroanthropology, including Daniel’s Language and Color, and my piece that the title of this one references, Sapir-Whorf hypothesis is right… sort of?
The subject of language learning’s effect on the brain is an especially important one for a number of reasons to us at Neuroanthropology (other than our tendency to flog the occasional dead horse); not only is language a frequent surrogate for more amorphous concepts like ‘culture,’ but it is also one of the capacities that, due to the work of Chomsky, is frequently believed to have innate foundations in the brain. Chomsky’s discussion of a language function innate in all human brains provides one of the foundational texts for much broader, sweeping assertions about ‘massive modularity’ in the brain covering a wide variety of functions.
Work by Kay’s team focused on the brain hemisphere used to classify colours. They tested subjects by showing them coloured targets randomly in their visual fields, and then seeing how long subjects could shift attention to the targets. As Smith writes:
It is well known that in adults, perception of colour is processed predominantly by the left hemisphere, which is also where most people process language. Studies have shown that the language one speaks can have an impact on the colour one sees.
Because adults use their left hemisphere to categorize colours, they can do perceptual tasks requiring colour categorization faster in the right visual field (the one that the left hemisphere links to). So, as we might expect, adults could shift to coloured targets in their right visual field faster. A variety of studies suggest that the the faster categorization in the right visual field is the result of influence from the lexical capacities of the left hemisphere. I have no problem with this, although I’m still not entirely persuaded that I want to call the ability to visually shift to coloured targets an act of ‘categorization.’ (But I just get hung up on the use of linguistic-based terms to shade over into activities that are only analogous, or, perhaps worse, might be accomplished through language, but also might not be. But I digress…)
The interesting twist on this report is that the team also tested pre-linguistic infants, from four to six month olds. Unlike the adults, the children were able to do perceptual tasks requiring colour categorization faster in the left visual field, suggesting that colour perception is a right hemisphere phenomenon in 4- to 6-month-olds. As the abstract to Franklin et al. (2008) explains: ‘The findings suggest that language-driven [category perception] in adults may not build on prelinguistic [category perception], but that language instead imposes its categories on a [left hemisphere] that is not categorically prepartitioned.’
The article by Smith goes on to discuss a couple of other interesting research papers (one of which I might return to in another post), but I found this instability in colour perception fascinating. The data suggests that there might be a discontinuity in the way that people categorize (and perceive, more importantly) colours between infancy and later life. The pre-linguistic way in which infants perceive colour may not necessarily be the foundation for colour perception later on, once a child learns language.
In other words, instead of having a part of our brain which categorizes colours, we have at least two ways we could do it, one that only emerges after we’ve learned language. I suppose that, at least in the populations that the Berkeley team were testing, the later-to-arise language-related categorizing capacity seems to displace the earlier way of accomplishing the task. Of course, it might not wipe out the earlier capacity, and it might emerge under duress or if there was some organic problem with the left hemisphere, dominant solution (which might be language based).
This seems to me to be a very good example of a simple function being accomplished in diverse ways within the brain, even if one way is dominant under most circumstances. Not so much a colour categorization ‘module’ as a brain that solves perceptual problems with the tools at its resources, using language or a left hemisphere ‘node’ of some sort, when it used to accomplish the same function in a different way before the emergence of the new capacity.
Franklin, A., G. V. Drivonikou, L. Bevis, I. R. L. Davies, P. Kay, and T. Regier. 2008. Categorical perception of color is lateralized to the right hemisphere in infants, but to the left hemisphere in adults. Proceedings of the National Academy of Sciences (PNAS) 105(9): 3221-3225