Monday, September 27, 2010

can language affect blood flow?

Do languages affect blood flow in the brain differently? Apparently, yes! In a recent fMRI study, researchers showed that Cantonese verbs and nouns are processed in (slightly) different parts of the brain than English nouns and verbs in bilinguals. The researchers used a lexical decision task to contrast the processing of English and Cantonese verbs and nouns in the brains of bilingual speakers.

Chinese nouns and verbs showed a largely overlapping pattern of cortical activity. In contrast, English verbs activated more brain regions compared to English nouns. Specifically, the processing of English verbs evoked stronger activities of left putamen, left fusiform gyrus, cerebellum, right cuneus, right middle occipital areas, and supplementary motor area. The cognition of English nouns did not evoke stronger activities in any cortical regions.

This is truly language affecting thought, no? The point of general interest to linguist is that bilingual speakers seem to process words in their two languages differently. Cantonese words are processed using diffuse brain regions and English words are processed using localized regions (this is a simplified explanation of course).

Now, I have to admit that this is not my specialty so I am not familiar with the background literature. However, as interesting as this is, I must say I have some serious questions about their methodology and underlying assumptions. I

First, they use orthography as their base for determining the "similarity" and "complexity" of languages. That is, if two languages use an alphabet, they are considered similar. While they give some passing references to other linguist measures, ultimately it is orthography that they use to compare "complexity" of stimuli (their word, not mine). So, they compared the mean number of strokes in a Chinese character with the number of letters in an English word to determine which was "more complex" than the other. I found this weird.

Then they made an assumption that Cantonese words are more ambiguous with respect to parts of speech. I do not klnow if this is true, but it certainly is true that English has plenty of POS ambiguity (just ask Eric Brill), so it's not obvious to me that this is a fair assumption. Furthermore, they provider no evidence for this. Unfortunately, they do not publish their actual sets of stimuli, so it's not possible (this morning while googling around) to look at which words they actually use, but I suspect there's plenty of ambiguity to be found in the English words.

Based on earlier work, they conjecture that morphological simplicity leads the brain to distribute where words are processed in the brain:

...a recent fMRI study examining monolingual Chinese adults in our own laboratory indicated that Chinese nouns and verbs activate a wide range of overlapping brain areas (without a significantly different network) than those reported in the English studies cited above (Li et al., 2004). Relatively fewer distinctive  grammatical features of nouns and verbs at the lexical level are likely to be responsible for this finding, but the question may be addressed more directly by employing bilingual individuals.

And the corollary should be true: the fact that English has tense and number markings means English verbs and nouns are processed ion more isolated parts of the brain. This is my wording of their conjecture. I may be oversimplifying just a bit, but I'm trying to wrap my head around the underlying claim. It's not clear to me why this would be true.

Next (and this may be a bit nit-picky), they judged the level of bilingual proficiency using a self-assessment questionnaire. Call me a cynic, but I just don't trust people's perceptions of their own language skills.

Then, the researches used frequency data from really dated sources including Francis and Kuceras 1982. I love F&K as much as the next guy, but in the age of the BNC, Davies's freely available 400 million word COCA, and the redonkulous Web 1T corpus of 1 trillion words (yes, 1 Trillion!), I see no reason to use resources so old.

Their basic conclusions are a tad confusing too. They never clearly explained the connection between bilingualism and morphological complexity, imho. The interplay is complicated and requires thorough discussion, which they simply did not provide. When I used to teach writing to college freshmen, I always told them that their job when writing a paper was to make my job as a reader easy. Explain things clearly so I don't have to work too hard to figure out what you mean. These authors failed to make my job easy. I had to figure things out too much for myself.

Ultimately, they found something interesting, I'm just not sure what it means and without more thorough linguistic vetting of their underlying assumptions, their results remain a head scratcher.

Chan, A., Luke, K.K., Li, G., Li, P., Weekes, B., Yip, V., & Tan, L.H. (2008). Neural correlates of nouns and verbs in early bilinguals. Annals of the New York Academy of Sciences, 1145, 30–40. (pdf)
Chan, A., Luke, K., Li, P., Yip, V., Li, G., Weekes, B., & Tan, L. (2008). Neural Correlates of Nouns and Verbs in Early Bilinguals Annals of the New York Academy of Sciences, 1145 (1), 30-40 DOI: 10.1196/annals.1416.000

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