WHO defines stuttering as disorders in speech rhythm during which the person who stutters knows what they want to say, but they are unable to do so due to involuntary blocks, repetitions and prolongations of sounds or words.

How is it that stuttering is common in almost all cultures across the world? Does language have any impact on stuttering? If someone speaks more than one language, do they stutter equally and similarly in all of them?

Defining, observing and treating stuttering is comparatively easy when the speaker is monolingual. When the person speaks and stutters in more than one language, it results in additional complexity.

What Is Bilingualism?

1% of the world’s population stutters, but more than 60% of the world’s population is bilingual. There is a high chance that speech-language pathologists (SLPs) encounter one or more individuals daily, who stutter and speak more than one language.

There is no universally-accepted definition of bilingualism. The term typically refers to the simultaneous and alternating use of two languages by an individual. It can also signify the individual’s fluency in one language and a limited extent of knowledge in a second language.

In past research, “bilingualism” has been referred to as “the use of two or more languages” (Borsel et al, 2000).

Manifestation of Stuttering in the Bilingual Population

Over the last few years, attention has shifted to the incidence of stuttering in the bilingual population. According to a literature review by Borsel et al in 2000, stuttering may be more prevalent in people who speak two or more languages, as compared to people who speak just one.

According to Nwokah (1988), a bilingual individual may stutter in both languages, but the disfluencies can manifest differently in each language. The review further states that the speech disfluencies may affect one or all the languages equally.

There are rare cases when the individual may experience a higher frequency and intensity of stuttering in a particular language. At the same time, the individual may be almost fluent in another language.

Nwokah suggests that in such cases, the individual might be significantly more proficient in conversing in one language as compared to the other.

What Are the Different Types of Bilingualism?

Everyone who speaks more than one language has picked up the second language either at a very young age (simultaneously with their first language), during elementary school (7 to 12 years old) or high school, or later in life (12+ years of age).

Au-Yeung et al (2000) categorized bilinguals into three broad groups that have helped speech-language pathologists (SLPs) note their observations on the link between stuttering and bilingualism.

i. The early bilinguals

These are individuals who began learning a second language almost simultaneously with their first language or mother tongue (simultaneous bilingualism). They completed acquiring and mastering the second language by the time they were 6 years old.

ii. The middle bilinguals

Individuals who have begun learning the second language between the ages of 7 and 12 years. Travis et al and Mussafia et al have studied and discussed consecutive bilingualism in their respective work.

iii. The late bilinguals

These are people who have begun the acquisition of the second language after the age of 12. They may have also chosen to learn the second language later in their teenage years or in adulthood.

What Is The Prevalence Of Stuttering In Bilinguals?

In one of the earliest studies on bilingualism and stuttering conducted by Travis, Johnson and Shover (1937), the stuttering prevalence among 4,827 children surveyed were around 1.80%, 2.80% and 2.38% for monolingual (English-speaking) kids, children who spoke two, and more than two languages in addition to English respectively.

The study subjects were between 4 and 17 years old. 2405 participants in the study were boys and 2,422 were girls. The determination was based on observation of the subjects’ reading, and conversation fluency in all languages.

An interpreter was present for children who spoke languages other than English.

The results showed that the stuttering prevalence was significantly lower in monolingual children (1.80%) as compared to those who speak two or more languages (2.80% and 2.38% respectively).

A similar study by Stern in 1948 involved 1861 children from 4 different schools in Johannesburg (South Africa). It showed that stuttering prevalence was 1.66% in monolingual and 2.16% in bilingual children.

At the same time, the severity rate of stuttering was much higher in bilinguals who stuttered as compared to monolinguals who stuttered.

However, both studies had one major drawback – the clinical judgments were based on single assessment only. According to Ingham and Costello (1984) single assessment studies are not enough to report stuttering like disfluencies.

A working alternative is the introduction of self-reports that can gather data including age, gender, ethnic background, education levels, occupational background, age of learning the second language etc.

Except for the research published by Au-Yeung et al (2000), the available data shows that stuttering prevalence is much higher in people who speak two or more languages as compared to those who speak only one language. Studies published by Travis et al indicate a direct link between bilingualism and stuttering.

Factors That Influence Stuttering In A Bilingual Population

A significant percentage of the world’s population is bilingual, but only 1% of the total population stutters. While there’s not much we know about the percentage of people who stutter covertly, we do know that not everyone who is bilingual has or had speech disfluency.

In 1937, Travis et al suggested a direct link between stuttering and bilingualism. For almost 26% of those who stuttered, there was a relationship between the introduction of a second language with the onset of their stuttering.

In another study by Pichon and Borel-Maisonny (1964), there was a strong suggestion that stuttering could be ascribed to bilingualism in 14% of their subjects.

So, what are the factors that influence the prevalence of stuttering in a bilingual population?

Synaptic Overload

Karniol suggested that in order to determine a direct link between stuttering and bilingualism, one has to consider the probability of synaptic overload. The 1992 study referred to a neuroscience model proposed in a 1989 study by Nudelman et al. The model proposes that speech disfluencies may reflect instances of instability in the language acquisition, processing and production loop in the brain.

Demands and Capacities of Language Processing

Another model Karniol and other researchers have considered and dismissed is the Demands and Capacities model by Starkweather (1987). According to this model, a child shows stuttering-like-disfluencies when they lack the capacities to meet the fluency demands of more than one language.

Genetic Predisposition and Environmental Factors

Travis et al also noted that 97.2% of the bilinguals who were also a part of the same study, didn’t stutter at all. Similarly, Mussafia observed in his study that children were susceptible to speech and language disorders when they have to pick up a second language suddenly and abruptly.

Other factors Travis et al considered in their research included –

• The economic insecurity in the homes of migrants whose children typically spoke more than one language
• The stress and confusion of moving from one state or country to another
• The stress of picking up a new language that is not typically spoken at home of migrant children

Possibly, the most important and relevant observation regarding the relationship between bilingualism and stuttering comes from the studies of Lebrun and Paradis (1984). They mention that stuttering may be a result of the input of mixed language utterances around children who are already predisposed to stuttering.

Brain Structures Involved in Language Acquisition and Processing

In 1997, imaging studies published by Kim et al on late bilinguals showed that second and native languages were spatially distinct in the Broca’s area. Whereas, in the case of early and middle bilinguals the native and second languages are represented in the common frontal cortical areas.

The same study inspires the discussion that the middle and early bilinguals are more susceptible to stuttering due to high demands of functioning of the same brain areas for both languages.

Limitations In The Research On The Link Between Bilingualism And Stuttering

There isn’t enough research to indicate the reason behind the strong link between stuttering and bilingualism.

Another link that remains to be investigated is the one between the similarities of the two or more languages spoken by the children who stutter.

The current hypothesis is that two closely related languages may lead to further confusion and more disfluencies in children who have picked up the second language later in life.

A contradictory hypothesis is that two unrelated languages may require more resources and cause more disfluencies in children predisposed to stuttering.

However, one of the most common observations in studies by Au-Yeung et al, and Travis et al is that disfluencies are less common among middle bilinguals as compared to early and late bilinguals. Nonetheless, the apparent “immunity” of adults towards the development of stuttering is unclear.

So, What Can We Tell About Stuttering and Bilingualism?

There is more to bilingualism and stuttering than we currently know. Last six decades of studies and research show that children (predisposed to stuttering) who picked up a second language while staying in a vulnerable or new environment have grown up to retain their stutter.

It is for certain that the middle bilinguals are more susceptible to stuttering as compared to early and late bilinguals.

There is no saying whether a person will stutter similarly in all the languages they speak. We must not forget that stuttering is highly heterogeneous. Apart from genetic predisposition, anomalies in the brain structure and possibilities of synaptic overload, there might be other factors that scientists and SLPs are yet to explore.