Can the daily use of two or more languages impact cognitive capacity?

Question

I've read the following threads:

• Is it possible to think in a second language?
• Does language and/or culture affect an individual's cognitive capacity?
• is it possible to think without language?

Language is clearly a very good tool for structuring ideas and communicating. I want to know if there is a correlation between cognitive capacity (in the same way CheeseConQueso expressed it) and using two or more languages fluently.

The following questions might help define what I'm wondering:

• Is it possible for someone who uses two or more languages daily to switch between "thought languages"?
  • If so, would it help broadening one's conceptual skills and adaptability?
• What language combinations would then be better mixed together?

Answer 1

A lot of research seems to have been done on the challenges multilingualism poses for the human brain, but not so much on how much actually meeting those challenges improves one's overall cognitive capacity. At present the general approach seems to be summed up: "Cognitive science suggests that the brain has selective resources with limited capacity" (Emily Holmes et al.). Stanislas Dehaene in particular asks, "How can cerebral circuits that normally handle a single phonology, lexicon and syntax adapt to the storage of multiple language systems?", and suggests that "sophisticated mechanisms of segregation must exist to prevent cross-talk." These can be witnessed in action when "anyone trying the well-known party trick of reciting the number sequence while switching languages (for instance un, two, trois, four, cinq) will recognise that central coordination is a very plausible source of difficulty in translation and language switching." Source of difficulty maybe, but not yet apparently evidence of positive capacity for other tasks. Hopefully some work has gone down that road since.

References:

Holmes, E. et al. "Can Playing the computer game 'Tetris' reduce the Build-Up of Flashbacks for Trauma? A proposal from Cognitive Science" Abstract. http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0004153

Dehaene, S. "Fitting two languages into one brain" Brain (1999) 122(12)

Since this answer I have indeed found some reports on the beneficial cognitive effects of bi- if not multi-lingualism:

Researchers said the extra effort involved in using more than one language appeared to boost blood supply to the brain and ensure nerve connections remained healthy - two factors thought to help fight off dementia. "We are pretty dazzled by the results," Professor Ellen Bialystok of Toronto's York University said in a statement. "In the process of using two languages, you are engaging parts of your brain, parts of your mind that are active and need that kind of constant exercise and activity, and with that experience [it] stays more robust," she later told CTV television. (Bilingualism delays onset of dementia 23:22 12 January 2007 by New Scientist and Reuters)

So his team compared the age dementia symptoms appeared in some 650 natives of Hyderabad, India, over a six-year period. About half spoke at least two languages. This group's symptoms started on average four and a half years later than those in monolingual individuals. The same pattern appeared for Alzheimer's, frontotemporal and vascular dementia. The results also held true for a group of people who were illiterate, suggesting that the benefits of being bilingual don't depend on education (Neurology, DOI: 10.1212/01.wnl.0000436620.33155.a4). A leading theory as to why bilingualism may affect dementia involves the constant suppression of one language, and switching between the two. "This permanent switching and suppressing offers you constant brain training," says Bak. ("Learn une autre langue to hold off dementia" New Scientist 9 November 2013.)

Answer 2

To answer the question of the title, yes, bilingualism is beneficial in theory.

However, in practice, it is not so. In America we do not have a true bilingual system of education, so it is difficult to judge the success of bilingualism based on our public foreign language education. With about 90% of American High Schools offering and sometimes requiring a foreign language, the benefits of bilingualism (if immersion and high proficiency was not required) are observed to be limited at best.

Moreover, fully bilingual societies still have the same fluid intelligence overall. The nigh-universal Flynn effect isn't improved as societies become multilingual.

Moreover, if you consider my reasoning biased by social stratification, let's examine a more equal set of multilingual groups. Consider (a) the computer science major in college where each student is tasked with learning and using in detail several computer languages of many differing types and forms and (b) the foreign language major. They score well on IQ tests, but so do many other majors not intrinsically requiring immersion into multilingualism.

Yes, switching the languages of thought is a non-task. I do not think (but I cannot prove) there are any advantages to the non-task.

In Computer Science (and computer scientists have multilingual brains.) a diverse set of languages from multiple paradigms are taught as a general rule of thumb. This is done so that one is familiar with all the basic concepts of linguistics (declarative, imperative and functional come to mind). In spoken languages anthropology would point you to the most diverse set of languages to build a multilingual set of knowledge.

Though this is anecdotal, my IQ as measured by a trained psychologist (both times) did increase a small amount (5 points) after my training in Computer Science was finished.