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Bilingualism as a protection against the onset of symptoms of dementia

31 May

Bialystok, E., Craik, F. I. M., & Freedman, M. (2007). Bilingualism as a protection against the onset of symptoms of dementia. Neuropsychologia, 45(2), 459–464.

This entry discusses research in bilingualism which has had a lot of media presence.

Very briefly, Bialystok, Craik and Freedman examined whether bilingualism delays the onset of the symptoms of dementia. Amazingly, their findings suggest that it is the case that bilingualism protects against the onset of the symptoms of dementia; however, as will be discussed, their results must not be generalized too much.

Initially, let’s look at how Bialystok and her colleagues designed their methodology. The researchers looked at 184 patient reports from the Memory Clinic at Baycrest in Toronto, Canada. The reports documented, amongst a lot of other factors, (1) the patients’ language backgrounds (e.g. whether they were bilingual or not) and (2) the age of onset of cognitive impairment (this age was determined in an interview during which a neurologist asked the patients and their caregivers at which age the symptoms were first noticed). Bialystok et al. then compared this age of onset of the symptoms of dementia in the monolinguals (49% of their population) with that of the bilinguals (51% of their population). Indeed, they found that there was a significant difference between the age of onset of the symptoms of dementia in the monolinguals and the bilinguals. Specifically, the bilinguals showed symptoms of dementia 4.1 years later than the monolinguals. All other factors, e.g. level of education, were considered to be equal, so it could be claimed that the “groups do not differ apart from their language abilities” (p. 462).

However, some interpretations of their results incorrectly suggest that learning a second language prevents dementia. This interpretation of their results is misleading for three reasons. Firstly, the bilinguals Bialystok et al. examined were people who “spent the majority of their lives, at least from early adulthood, regularly using at least 2 languages” (p. 460). It would therefore be incorrect to infer from their study that, for example,  attending an evening course to learn a foreign language in late adulthood could delay the onset of the symptoms of dementia (this might be the case, but their study didn’t examine such individuals, who, I emphasize here, could nevertheless arguably be considered to be bilinguals). Secondly, it would be incorrect to infer from their study that bilingualism prevents dementia. The bilinguals were just as likely to be diagnosed with dementia, it was simply the case that the diagnosis occurred on average later in the bilinguals than in the monolinguals, i.e. the onset of the symptoms of dementia was delayed in the bilinguals. Finally, the researchers suggest that (a specific type of) bilingualism is a protection against the onset of the symptoms of dementia. It may very well be that the bilinguals in their study actually acquired dementia at, on average, the same age as the monolinguals; crucially, it can only be claimed from their study that in the bilinguals the symptoms surfaced later than in the monolinguals (or, even more critically, that these symptoms were noticed later in the bilinguals than in the monolinguals).

However, if it is accepted that their findings indicate that (a certain type of) bilingualism delays the onset of the symptoms of dementia (and it seems that this would be a valid conclusion), there are practical implications. For example, it appears that raising a child in a bilingual environment has benefits in old age in addition to those potentially evidenced earlier on. Moreover, maintaining bilingualism instead of monolingual assimilation could postpone the onset of the symptoms of dementia in rather large immigrant populations.

Overall, Bialystok et al.’s results are truly amazing, indicating that the effects of bilingualism extend far beyond the immediate benefits of knowing more than one language.

Esther de Leeuw

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