The Bilingual Brain
Understanding the bilingual brain with the help of neuroimaging techniques
Posted Aug 12, 2013
Post written by François Grosjean.
In 1978, researchers Martin L. Albert and Loraine K. Obler wrote a highly influential book, The Bilingual Brain, which gave great momentum to the neuropsycholinguistic study of bilingualism, but also offered, as it happens, a very catchy title to talk about it. For the next twenty years, researchers concentrated on such topics as bilingual aphasia (see here) and the lateralization of languages in bilinguals. Various experimental techniques involving listening, reading and finger tapping were used to see if the involvement of each hemisphere (left and right) was the same or not in monolinguals and bilinguals, and, for the latter, whether this depended on the type of bilingualism. Unfortunately, clear and definitive answers were never obtained, despite what is stated in the more popular press and in some general public books.
With the advent of neuroimaging techniques such as event-related potentials (ERPs) and functional magnetic resonance imaging (fMRI), much more sophisticated research could be undertaken in an attempt to understand how the brain organizes and processes the bilingual's languages. In this post I will describe a research project initiated by Penn State University Professor Ping Li which lasted some seven years and involved researchers from the USA, Hong Kong, China and the United Kingdom.
In a first study, Li and his coauthors wanted to find out whether verbs and nouns in Chinese are represented in the same way in the brain as are their counterparts in English: verbs in the frontal region of the brain and nouns in the posterior region. The authors noted that verbs and nouns in Chinese do not contain grammatical markers as do similar words in English and other Western languages. In addition, many Chinese verbs can occur as subjects, and nouns as predicates. Finally, Chinese has a much higher number of ambiguous words than English that can be used either as a noun or a verb (e.g. "huihua" means both to draw and a drawing).
Native speakers of Chinese took part in an imaging (fMRI) study in which they were presented with the written version of two-character Chinese words as well as nonwords (lexical items that looked like words but weren't). They were asked to decide whether what they saw was a real word or not. The results the researchers obtained were that nouns and verbs in Chinese were not confined to specific brain regions, as in English; rather they activated a wide range of overlapping areas, in both the left and the right hemisphere. The authors explained the involvement of the right hemisphere (language is usually lateralized in the left hemisphere in right-handers) because of the visual features of Chinese characters and the lexical tones carried by Chinese words.
Having shown that very different languages, in this case English and Chinese, have different neural representations for nouns and verbs, the interesting question became: What about bilinguals who store and process these two languages? Researcher Alice H. D. Chan of the University of Hong Kong along with six other researchers, among them Ping Li, addressed this question. Their participants, this time, were early Chinese-English adult bilinguals who had started to learn each language before the age of 3 on average. They were asked to do the same task as above, first in one language and then in the other.
The researchers found that Chinese nouns and verbs involved activation of common brain areas (thus replicating the first study) whereas English verbs engaged many more regions than did English nouns. They concluded that under specific conditions, bilingual learners may deal with word information of the two languages separately. Thus, when word class is an important marker during language development, as it is in English, early bilinguals will acquire this language-specific property. In sum, the bilingual brain is highly plastic.
But is this true of late bilinguals? A third study, this time headed by researcher Jing Yang also of the University of Hong Kong, along with two other researchers including Ping Li, answered this question. The participants they used were native Chinese adults who had began to learn English at age 12 on average. They too showed no significant differences in brain activation for nouns versus verbs in Chinese (once again replicating the earlier study) but, to the surprise of the researchers, they showed little neural differentiation of nouns and verbs in English, unlike the early bilinguals.
The authors concluded that when a second language is acquired later, such as in adolescence, the linguistic experience one develops for one's native language can shape the neural representation of the second language. This said, they noted aspects of their data that seemed to show that with more linguistic exposure to English, and hence improved language proficiency, the late bilinguals may yet develop neural sensitivity to noun-verb differences in their second language.
These three studies are a fine example of how modern imaging approaches can contribute to our understanding of how the bilingual brain organizes and processes languages, and how the degree of overlap of languages, as well as age of onset of the second language, play an important role at the neuropsycholinguistic level.
Photo of an artistic representation of a head from Shutterstock.
Li, Ping, Jin, Zhen & Tan, Li Hai. (2004). Neural representations of nouns and verbs in Chinese: an fMRI study. NeuroImage, 21, 1533–1541.
Chan, Alice H. D., Luke, Kang-Kwong, Li, Ping, Yip, Virginia, Li, Geng, Weekes, Brendan & Tan, Li-Hai. (2008). Neural correlates of nouns and verbs in early bilinguals. Annals of the New York Academy of Sciences, 1145, 30-40.
Yang, Jing, Tan, Li-Hai & Li, Ping. (2011). Lexical representation of nouns and verbs in the late bilingual brain. Journal of Neurolinguistics, 24, 674-682.
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