Have there been any studies that study the effect of having two first languages (simultaneous bilingualism) on the capacity of learning second languages later? If so, what was their result?
A relevant study (abstract at PubMed) was carried out at Northwestern University. They took 20 monolingual (presumably English) speakers, 20 English-Mandarin speakers, and 20 English-Spanish speakers. They then introduced them to a completely unrelated constructed language. The bilinguals successfully remembered about twice as many words as the monolinguals. An article on a similar study can be found here, using Russian-Hebrew bilinguals and Hebrew monolinguals.
It seems reasonable that bilinguals would be more adept at learning a second language closely related to one of the languages they speak than an individual who only speaks one of the languages, but the study shows that this holds even in the case of an unrelated case.
Sanz (2000) looked at 201 students (77 monolinguals and 124 bilinguals, knowing Catalan and Spanish) from roughly the same geographical and educational background (Jesuit schools in urban northern Spain). The students learned English via a combination of methods. The bilinguals outperformed the monolinguals.
One more thing to consider is that one of the languages can act as a bridge to learning a third language. For example, if a person is fluent in languages X and Y, and Y is closely related to both X and Z but X and Z are not closely related, it will be easier for the person to learn Z than it would be for a person who is only fluent in X.
In general language learners tend to acquire more learning skills which may quicker the progress of learning another language. However efficiency of learning another language largely depends on similarity and certain aspects of the languages already learnt in terms of fundamental differences such as words (also letters if different), grammar, conjugations, and sentence structure. It also strongly depends on the method used and your own unique learning abilities (some gifted people can learn any language in just few weeks).
Having learnt already two first languages makes you more aware of the language (e.g. concept of word as a component), especially how it's structured and manipulated. And these skills makes you more effective communicator, editor or writer. Also when you speak language, you develop a better ear for listening (e.g. distinguishing meaning from discreet sounds).
For example one Cambridge study from 1993 tested the levels of word awareness which shown no significant difference in the performance of two tested groups (the marginal bilingual and the monolingual group), however second round of tests after few months found that the children in the marginal bilingual group ‘were showing a significantly higher level of word awareness than their monolingual counterparts’p. 436.
Study: A1: Yelland, G., J. Pollard and A. Mercuri (1993) The metalinguistic benefits of limited contact with a second language. Applied Psycholinguistics 14: 423-444.
List of other studies related to benefits of bilingualism:
- Swain, M. and Lapkin, S. (1991) Additive bilingualism and French immersion education: the roles of language proficiency and literacy. In: Reynolds, A. Bilingualism, Multiculturalism, and Second Language Learning. The McGill Conference in Honour of Wallace E. Lambert. New Jersey: Lawrence Erlbaum Associates, pp203-216.
- Bialystok, E. (1987) Development of word concept by bilingual children. Studies in Second Language Acquisition 9: 133-140.
- Liddicoat, A. (2001) Learning a language, learning about language, learning to be literate. Babel Vol. 35, 3: 12-15.
- Baker, C. (2006) Foundations of Bilingual Education and Bilingualism. (4th Edition) Clevedon: Multilingual Matters.
- Ianco-Worrall, A. (1972) Bilingualism and cognitive development. Child Development 43, pp 1390-1400.
- Ben-Zeev, S. (1977) The influence of bilingualism on cognitive strategy and cognitive development. Child Development 48, pp 1009-1018.
- Eckstein, A. (1986) Effect of bilingual program on English language and cognitive development. In M. Clyne (ed) An Early Start. Melbourne: River Seine, pp 82-98.
- Bialystok, E. (2001) Bilingualism in Development: Language, Literacy and Cognition. Cambridge: Cambridge University Press.
- Bialystok, E., Craik, F., Grady, C., Chau, W. Ishii, R. Gunji, A., Pantev, C. (2005) Effect of bilingualism on cognitive control in the Simon task: evidence from MEG. Neuroimage 24, pp 40-49.
Above studies are well summarized in Report to the Department of Education and Training by Sue Fernandez, Research Unit for Multilingualism and Cross cultural Communication at the University of Melbourne.
So in general, several studies have shown that bilingual people (mostly children) have an advantage over monolingual people for certain tasks which involve this aspect of language, including some aspects of word awareness (e.g. Bialystok 1987).unimelb. Therefore speaking two or more languages is a great asset to the cognitive process since the brains of bilingual people operate differently than single language speakers which can offer several mental benefits.