Serendip is an independent site partnering with faculty at multiple colleges and universities around the world. Happy exploring!

Bilingualism and Stuttering

Bo-Rin Kim's picture

Having spent ten years of my life in Korea and the other eleven in America, I consider myself to be bilingual even though I am more comfortable in English. I was at the peak of my bilingual ability when I attended an international school in Korea. My English was strong because it was the language I used at school, and my Korean was improving daily as I interacted with the culture I lived in. However, after coming to America for college, I found myself having to adjust back to the Korean language every time I went home. It felt unnatural to use the language, and I would at times catch myself stuttering when speaking Korean.  It seemed to make intuitive sense that transitioning from one language to another would provoke some anxiety and difficulty in speech, but does switching between two languages cause stuttering? What is the neurological basis of stuttering and does being bilingual make one more susceptible to stutter?

Stuttering is defined as “a speech disorder in which sounds, syllables or words are repeated or prolonged, disrupting the normal flow of speech” (7). Muscle movements that control breathing, articulation and voice production coordinate to produce normal speech. The brain is responsible coordinating these muscles in response to thoughts and cognitive processes. Disruptions in this coordination are thought to cause stuttering although the exact causes andcognitive processes underlying stuttering are unknown. Researchers have, however, identified that genetic, developmental, psychological and neurological factors contribute to the onset of different types of stuttering. Developmental stuttering occurs in children during speech development when they lack the verbal skills necessary for their verbal demands.  This type of stuttering is usually outgrown. Neurogenic stuttering arises from brain injury that disenables the brain’s ability to coordinate signals to the various muscles involved in speech production. Rarely, psychological factors like mental illness or chronic stress can giverise to a psychogenic form of stuttering. Researchers have also noted that stuttering runs in families, showing a strong indication of its genetic nature, but there is no scientific evidence to support this statement (7).

However, there has been evidence indicating that stuttering may arise from how the brain processes linguistic information, which indicates a neurological basis of stuttering. Functional imaging has shown that the brains of stutterers and non-stutterers engage in different activation patterns when performing speech-related tasks. Positron Emission Topography (PET) scans taken of subjects as they orally read a list of words showed that stuttering subjects had greater amounts of brain activity in both hemispheres compared to non-stuttering subjects (3). The large amount of brain activity induced by verbal tasks shows that speech is not an automatic process for stutterers, but is one that requires a lot of effort. Moreover, PET scans taken of stutterers and non-stutterers as they completed a silent reading task revealed that stutters had more activity in their anterior cingulate cortex. This area of the brain is involved in anticipatory reactions and the preparation of responses to complex tasks. Greater activation in this area indicates that stutterers may be scanning the words they read for potential fluency problems and silently rehearsing these words (3). These findings show that stutters engage in more cognitive speech processing compared to non-stutterers. A neural basis of stuttering has been further supported by PET scans showing significant decreases in the brain activity of stutterers a year after they completed behavioral speech therapy. This indicates that over a prolonged period of training, the mechanisms involved inproducing fluent speech become engrained into an automatic process that requires less cognitive attention (3). These research findings show that stuttering is related to high levels of cognitive or neural activity and a decrease in such activity is related to a decrease in stuttering.

Another study that looked at the cognitive capacities of stutterers found that stutterers are more sensitive to cognitive load. That is, there are not able toperform as well as non-stutterers in complex tasks that require a lot ofcognitive effort. In one such task, subjects had to identify whether a pair ofwords rhymed or not. The word pairs either looked alike and rhymed, looked alike and did not rhyme, did not look alike and rhymed, or did not look alike and did not rhyme. The reaction times of stutterers were significantly slower than those of non-stutterers when the phonology and appearance of the words did not match (8). Identifying words that do not look alike yet rhyme (“cone” and“own”) or words that look alike but do not rhyme (“gown” and “own”) are more difficult tasks and demand more cognitive attention than identifying words that look alike and rhyme. These findings suggest that stutterers are not able to deal with cognitive stress as well as non-stutterers. In light of the research with PET scans discussed above, stutterers already use more cognitive energy than normal to process speech. Thus, when the incoming verbal information becomes complex, they may not have the cognitive capacity or attention to quickly process it.

The problem with all the studies discussed above is that they cannot prove a causal relationship between cognitive load and stuttering. They do not determine whether increased cognitive activity causes stuttering or if stuttering causes the increased cognitive activity. Moreover, if cognitive hyperactivity gives rise to stuttering, where does this increase in cognitive processing come from? One source of increased cognitive load is being bilingual. Bilinguals have to frequently switch from one language to another and suppress the language thatis currently not in use (2, 6). However, a significant portion of research done on the cognitive effects of bilingualism shows that bilingualism positively affects cognition. Researchers have found that bilinguals are better at selective attention, abstract thinking, switching between tasks and creative thinking (1, 2, 6). The increased cognitive load brought on by bilingualism seems to train the brain to be flexible in thought rather than overloading the brain, decreasing its ability to effectively process information.

However, researchers have also found that these cognitive benefits only apply to balanced bilinguals. For the brain to acquire true flexibility and the cognitive benefits of being bilingual, fluency in the two languages must be similar (1). Perhaps stuttering is prone to occur in imbalanced bilinguals, like myself, who experience the cognitive load brought on by processing two languages, but who have not acquired the cognitive benefits of being bilingual. Studies have indeed found that imbalanced bilinguals tend to stutter more intheir less dominant language (5). Researchers explain that imbalanced bilinguals have to perform two attention-demanding processes at the same time.They have to formulate words and syntax in their less dominant language, while suppressing interference from their native language, which is more automatically activated. Although imbalanced bilinguals showed more stuttering in their less dominant language compared to balanced bilinguals, balanced bilinguals were still found to stutter, to a lesser extent, in both languagesas well (5). So the question remains: does being bilingual make one more susceptible to stutter?

There has been a study that concluded that bilinguals are more prone to stutter. In this study, 317 stuttering children aged 8 to 10, who were enrolled in a speech clinic,were analyzed and compared to a control group of non-stuttering children. Ofthe stuttering sample, 69 children were bilingual and 38 of these primarily useda language other than English at home. 23 of the 38 children spoke both Englishand another language before starting school. The remaining 15 children learned English in school. In the non-stuttering group, 28 children learned English after starting school and only 10 children knew English before entering school. Researchers concluded that learning a second language before age 5 could increase the possibility of a child developing a stutter (4). They reason that children who learn two languages simultaneously in early childhood are more likely to stutter because of the heavy cognitive load brought by having to learn and differentiate two languages. This study supports the position that bilinguals are more likely to stutter due to the cognitive load they experience during early language development.

Although it presents interesting results, this study is flawed in several ways. First of all, only 21.8% of the stuttering sample was bilingual. Of these 69 children,only the 38 subjects who used a language other than English at home were focused on, which is a very small sample size. The other 31 bilingual, stuttering children were not looked at. The conclusion that bilingualism leads to stuttering does not seem very valid when bilinguals were a minority of the stuttering sample and when only bilinguals of such a specific background were looked at. It seems as if the researchers were trying to find whatever connection they could between bilingualism and stuttering and highlighted that finding even though it may not have been very significant in the big picture.

While this study only looked at a very specific subpopulation of bilinguals, it does indicate that cognitive load can lead to stuttering. Perhaps it is this cognitive load that comes frombalancing two languages that taxes the brain’s ability to efficiently process and produce the signals responsible for coordinating fluid speech. In balanced bilinguals, language processing is more automatic due to their high fluency, preventing them from experiencing such cognitive load and giving them morecognitive flexibility. Thus, imbalanced bilinguals, who need to make a conscious effort to construct their second language and suppress their first language, must be the ones who feel the most taxed by the cognitive load of knowing two languages.

Imbalanced bilinguals may have a type of stuttering similar to developmental stuttering, which results when the verbal skills of children do not meet their verbal needs. Although bilingual stuttering may not occur during language development, it can occur during a different stage of development when a second language is acquired and is frequently used. Bilinguals may have a flood of verbal thoughtsin either language, but their brains are not able to channel the large cognitive demand into clear, articulate vocalizations. Like children, imbalanced bilinguals are not able to coordinate the speech mechanisms necessary to project their thoughts. Since a significant portion of their cognitive energy is spent repressing one language while activating another, imbalanced bilinguals lack the cognitive attention needed to precisely coordinate their thoughts with the motor control needed for speech production.  

This is not to say that all imbalanced bilinguals are prone to stutter. It also depends on the individual’s selective attention, cognitive flexibility and cognitive capabilities. However, by tying together the research on stuttering and bilingualism, it seems reasonable to conclude that the cognitive load produced by processing two languages can limit the brain’s ability to precisely coordinate verbal thoughts and speech production, which would result in stuttering. Hence, while there are numerous other factors that contribute to the onset of stuttering, having to speak in a second language you are not completely fluent in can lead to a cognitive overload that can cause stuttering.



1. Baker, C. (2001). Bilingualism and Cognition. In Foundation of Bilingual Education and Bilingualism (pp. 135-161). Clevedon, Great Britain: Multilingual Matters Ltd.

2.Bialystok, E. (2005). Consequences of Bilingualism for Cognitive Development.In J. Kroll & A. De Groot (Eds.), Handbook of Bilingualism (417-432). New York: Oxford University Press.

 3. Kroll,Robert M., and Luc F. De Nil. "Neural Bases of Stuttering and itsTreatment." The Stuttering Foundation. 20 Feb. 2009. Stuttering Foundation of America.22 Feb. 2009 <>.

 4. Liberman,Mark. "Does Bilingualism Cause Stuttering?" Weblog post. LanguageLog. 17 Sept. 2008. 22 Feb. 2009 <>.

 5. Lim, ValerieP.C., et al. "Stuttering in English-Mandarin Bilingual Speakers: TheInfluence of Language Dominance on Stuttering Severity." Journal of Speech,Language, and Hearing Research. 51 (Dec.2008): 1522-1537.

 6. Peal, E., & Lambert, W. E.(1962). The relation of bilingualism to intelligence. Psychological Monographs:General and Applied, 76(27), 1-23.

 7. "Stuttering." 2009. WebMD. 22 Feb. 2009 <>.

 8. "Stutteringmore than talk, research shows brain's role in disorder." Medical NewsToday. 26 July 2004. MediLexicon International Ltd. 22 Feb. 2009 <>.





Paul Grobstein's picture

bilingualism and stuttering

Intriguing, and raises some further interesting questions. Is stuttering more common in "unbalanced bilinguals"? Can it, in such cases, occur in one language and not in the other? If so, is it always in the less dominant language? That might say a lot about the cognitive load idea.