Have there been any studies into detrimental effects of language learning?

Question

There have been many studies into the varied benefits of being bilingual, but things are rarely uniformly beneficial.

Have there been any studies into whether or not there are detrimental effects to being bilingual (Aside from the opportunity cost of the time you spend learning)?

Answer 1

Yes, there have been studies showing some disadvantages.

Bialystok (2008) notes that

It is now well documented that bilinguals generally control a smaller vocabulary in each language than monolinguals (Oller and Eilers, 2002; Perani et al., 2003; Portocarrero, Burright and Donovick, 2007).

This has been found to be true in children, adolescents, and adults, although the author notes that

The bilingual deficits in lexical access and retrieval persist with aging (Gollan, Fennema-Notestine, Montoya and Jernigan, 2007), although a study by Gollan, Montoya, Cera, and Sandoval (2008) showed that the effects of aging interacted with word frequency in that older bilinguals demonstrated a smaller deficit for low-frequencywords.

Protocarrero et al. (2007) come to the same conclusion as Bialystok and the other studies cited.

While the reasons for this are not known, there are two competing theories:

1. Bilinguals, on average, use each language less often, and therefore reinforcement of different links is weaker in each language. Mindt et al. (2008) touch on this hypothesis a little.
2. Bilinguals may have worse abilities to recall words because their L2 language may have been learned significantly later than their L1.

Note that older studies believed that bilingualism caused a reduction in IQ (see e.g. Darcy (1953)). However, these studies were flawed and are no longer accepted as accurate.

There seems to be a consensus that bilingualism is, on the whole, an advantage, and various benefits are constantly touted. I'm not disputing those findings, but it's interesting to pay attention to the fact that there may be a bias towards studies that show that bilingualism is a positive thing, as this New Yorker article says (the cited study is de Bruin et al. (2014)).

A relevant phenomenon is code-switching, when a multilingual switches between multiple languages in the same sentence or conversation. The Linguistic Society of America says that this is not an issue for children talking bilingually at home. However, it makes sense that it could be disorienting in a conversation with people who speak only one language. That said, this is not a likely common problem, nor a severe one.

Answer 2

According to this paper, in general, bilinguals have smaller vocabularies for each language. They also match pictures to words and list common words at a slower pace. Most of the disadvantages fall under the category of lexical access. In my own experience, I started taking a while to recall some advanced English words around the time I started learning extra languages. I quote the paper's summary of the topic here:

Research with adult bilinguals built on these studies with children and reported two major trends. First, a large body of evidence now demonstrates that the verbal skills of bilinguals in each language are generally weaker than are those for monolingual speakers of each language. Considering simply receptive vocabulary size, bilingual children [23] and adults [24] control a smaller vocabulary in the language of the community than do their monolingual counterparts. On picture-naming tasks, bilingual participants are slower [25–28] and less accurate [29, 30] than monolinguals. Slower responses for bilinguals are also found for both comprehending [31] and producing words [32], even when bilinguals respond in their first and dominant language. Finally, verbal fluency tasks are a common neuropsychological measure of brain functioning in which participants are asked to generate as many words as they can in 60 seconds that conform to a phonological or semantic cue. Performance on these tasks reveals systematic deficits for bilingual participants, particularly in semantic fluency conditions [33–37], even if responses can be provided in either language [38]. Thus, the simple act of retrieving a common word is more effortful for bilinguals.

The studies referenced are these:

23. Bialystok E, et al. Receptive vocabulary differences in monolingual and bilingual children. Bilingualism: Language and Cognition. 2010;13:525–531. [PMC free article] [PubMed]
24. Bialystok E, Luk G. Receptive vocabulary differences in monolingual and bilingual adults. Bilingualism: Language and Cognition. 2011 [PMC free article] [PubMed]
25. Bialystok E, et al. Lexical access in bilinguals: effects of vocabulary size and executive control. J. Neurolinguistics. 2008;21:522–538.
26. Costa A, Santesteban M. Lexical access in bilingual speech production: evidence from language switching in highly proficient bilinguals and L2 learners. J. Mem. Lang. 2004;50:491–511.
27. Gollan TH, et al. Bilingualism affects picture naming but not picture classification. Mem. Cognit. 2005;33:1220–1234. [PubMed]
28. Hernandez, et al. In search of the language switch: an fMRI study of picture naming in Spanish-English bilinguals. Brain Lang. 2000;73:421–431. [PubMed]
29. Gollan TH, et al. The bilingual effect on Boston Naming Test performance. J. Int. Neuropsychol. Soc. 2007;13:197–208. [PubMed]
30. Roberts PM, et al. English performance of proficient bilingual adults on the Boston Naming Test. Aphasiology. 2002;16:635–645.
31. Ransdell SE, Fischler I. Memory in a monolingual mode: when are bilinguals at a disadvantage? J. Mem. Lang. 1987;26:392–405.
32. Ivanova I, Costa A. Does bilingualism hamper lexical access in speech production? Acta Psychol. 2008;127:277–288. [PubMed]
33. Bialystok E, et al. Cognitive control and lexical access in younger and older bilinguals. J. Exp. Psychol. Learn. Mem. Cogn. 2008;34:859–873. [PubMed]
34. Gollan TH, et al. Semantic and letter fluency in Spanish-English bilinguals. Neuropsychology. 2002;16:562–576. [PubMed]
35. Luo L, et al. Effect of language proficiency and executive control on verbal fluency performance in bilinguals. Cognition. 2010;114:29–41. [PubMed]
36. Portocarrero JS, et al. Vocabulary and verbal fluency of bilingual and monolingual college students. Arch. Clin. Neuropsychol. 2007;22:415–422. [PubMed]
37. Rosselli M, et al. Verbal fluency and repetition skills in healthy older Spanish-English bilinguals. Appl. Neuropsychol. 2000;7:17–24. [PubMed]
38. Gollan TH, Ferreira VS. Should I stay or should I switch? A cost-benefit analysis of voluntary language switching in young and aging bilinguals. J. Exp. Psychol. Learn. Mem. Cogn. 2009;35:640–665. [PMC free article] [PubMed]

Answer 3

Barely

Language learning has many benefits but I could find a few:

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Anxiety is the biggest one I found. Language learning can be a difficult process and it doesn't come as easily to some people. When students are having trouble learning a new language, getting more lost in a language can cause a great deal of anxiety for students. ^[source]

Wikipedia has divided language anxiety into three parts, communication apprehension, test anxiety ,and fear of negative evaluation. Communication apprehension is commonly caused by a deficiency in a specific part of a language. Test anxiety is more specific to students learning a language in a class room. Learning a language is a complex task, and being tested on it can be a daunting feeling for some. Additionally the fear of negative evaluation is also commonly caused in a class room, where a student is anxious due to feeling incompetent. Most causes of anxiety are due to a lack of confidence, or self-esteem. ^{[source][yet another source]}

"Cultural Discrepancies" This one applies more to children rather than adults. When learning a language you are exposed to its culture. For children, especially in teenagers can result in a tangle in the intimate connection between one's language and culture (but this isn't common). ^[source]

Language learning has so many positives, they greatly outweigh the negatives, so I hope this answer doesn't make you not want to learn a new language.

Those are the only negatives I could find though I'll update if I can find more.

Answer 4

There has been quite some research into the influence of a second language on a speaker's first language. A collection of papers on these topics has been edited by Vivian Cook (Effects of the Second Language on the First, Multilingual Matters, 2003).

Research suggests that even speakers who remain in their L1 community but acquire advanced skills in an L2 are influenced in their pronunciation of their mother tongue by the pronunciation of similar sounds in their second language. (Gillian Lord: Second Language Acquisition and First Language Phonological Modification; 2008)

More generally, Pavlenko: "L2 Influence on L1 in Late Bilingualism" (Issues in Applied Linguistics, 2000) claims to provide evidence that even in adult L2 learning and use, L2 influences L1 phonology, morphosyntax, lexis, semantics, pragmatics, rhetoric, and conceptual representations.

Any of these effects will be viewed as detrimental by the speaker themselves and/or by their L1 community as soon as it leads to noticeable divergence from the L1 norm.

Answer 5

Here's one showing that bilinguals did substantially worse than monolinguals on a test of the Stroop effect (the [dis]ability to correctly and quickly name the colors in which other color names are written; thought to predict a number of intelligence-related cognitive functions, including processing speed and selective attention):Journal of the International Neuropsychological Society.