New study links stuttering severity to heightened anxiety and altered sound processing in the brain

Adults who stutter experience differences in how their brains process sound, and these sensory differences tend to overlap with both stuttering severity and anxiety levels. A recent study published in BMC Psychology provides evidence that stuttering involves a complex interaction between sensory processing, emotional states, and speech production. The findings suggest that evaluating both neurological and psychological factors could improve therapies for people who stutter.

Stuttering is typically understood as a communication disorder that interrupts the physical flow of speech. People who stutter often experience involuntary repetitions, prolongations, or blocks in their vocal expressions. Most therapeutic approaches focus primarily on the motor aspects of speaking, treating the condition as an issue with the muscles and nerves controlling the vocal cords, tongue, and lips.

Agit Şimşek, an assistant professor in the Department of Speech and Language Therapy at İnönü University in Malatya, Turkey, designed a study to explore whether non-motor factors also contribute to developmental stuttering. “Stuttering has traditionally been viewed primarily as a speech motor disorder,” Şimşek said. “However, a growing body of evidence suggests that auditory processing and emotional factors may also play important roles in its clinical presentation.”

Şimşek, who is also the author of the book A Holistic Perspective on Stuttering, wanted to look beyond the physical mechanics of speech. “As a speech and language therapist and researcher, I have long been interested in understanding stuttering from a broader perspective,” Şimşek said. “This study was designed to examine how neurophysiological processes and anxiety levels relate to stuttering severity in adults who stutter.”

Previous studies have hinted that individuals who stutter might process sounds differently in their brains. Auditory processing refers to how the brain recognizes, interprets, and responds to sounds coming through the ears. This processing is heavily involved in fluent speech, as humans rely on an auditory feedback loop to monitor and adjust their own voices while talking.

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By combining brain wave measurements with psychological assessments, the author aimed to map out the broader neurological and emotional landscape of the communication disorder. “One important message is that stuttering is much more complex than simply ‘getting stuck on words,’” Şimşek said. “Our findings suggest that adults who stutter show differences in how the brain processes auditory information and also report higher levels of anxiety than fluent speakers.”

He noted that these results support the view that speech, brain function, and emotional experiences interact with one another and should be considered together when understanding stuttering. To investigate this, the study included 29 adults who stutter and 30 adults with no history of speech disorders. All participants were between the ages of 18 and 45.

The two groups were matched based on age, education, and biological sex to ensure fair and balanced comparisons. Şimşek verified that all participants had normal hearing through standard auditory tests. He also confirmed that all participants were right-handed, as handedness can influence which side of the brain handles language tasks.

A certified speech and language therapist evaluated the stuttering group using a standardized severity instrument to determine whether their symptoms were mild, moderate, or severe. To measure emotional states, participants completed a standardized questionnaire that evaluates both immediate anxiety and long-term anxiety tendencies. Immediate anxiety describes how a person feels in the current moment, while long-term anxiety refers to a person’s general personality trait.

To assess brain activity, the researcher used an electroencephalogram. This non-invasive tool involves placing small sensors on the scalp to record electrical signals, which are often called brain waves. The researcher specifically looked at event-related potentials, which are distinct electrical spikes and dips that happen in the brain milliseconds after a person hears a sound.

During the first part of the experiment, participants listened to a series of 250 short, pure tones through headphones. These standard tones were played at a frequency of 1000 Hertz. The equipment recorded the exact timing and electrical strength of the brain’s reaction to each sound.

The study tracked early brain wave responses, which show the exact moment a sound reaches the auditory cortex in the brain. It also tracked later responses, which reflect how the brain integrates that sound and prepares to react to it sensorily and physically.

In the second part of the experiment, participants completed a passive listening test designed to measure automatic auditory change detection. They listened to 500 tones, where 80 percent were the standard 1000 Hertz tone. The remaining 20 percent were slightly higher-pitched tones played at 1200 Hertz.

This unpredictable shift triggers a specific, automatic brain wave response when the brain notices an unexpected change in its environment. Compared to the control group, adults who stutter showed delayed and physically smaller brain wave responses across almost all measurements. The time it took for their brains to register the sounds was longer.

Additionally, the electrical strength of the response was generally weaker than in those who do not stutter. These brain wave differences were closely linked to the severity of a person’s stuttering. Participants with severe stuttering exhibited the most delayed and reduced responses in the early and middle stages of sound processing.

As stuttering severity increased from mild to moderate to severe, the brain’s processing speed and electrical response strength decreased in a progressive, step-by-step pattern. The psychological measurements showed that adults who stutter experience significantly higher levels of both immediate and general anxiety. Just like the brain wave patterns, anxiety scores increased alongside stuttering severity.

Those with severe stuttering reported the highest levels of daily anxiety. “One of the most interesting findings was the strength and consistency of the relationships between stuttering severity, anxiety levels, and neurophysiological measures,” Şimşek said. “We observed that individuals with more severe stuttering tended to show greater alterations in auditory cortical responses and higher anxiety scores.”

He explained that this pattern reinforces the idea that stuttering is a multidimensional condition rather than solely a speech motor disorder. Interestingly, the brain wave associated with detecting unexpected sound changes showed a unique pattern in individuals with severe stuttering. While the overall stuttering group had weaker responses to changing sounds than the control group, those with severe stuttering reacted faster and more intensely to the unexpected sounds than those with mild stuttering.

The researcher suggests this heightened reaction to unexpected sounds might be linked to elevated anxiety. High anxiety could cause the nervous system to become hypervigilant. This state of high alert might make the brain overly sensitive to sudden shifts in the auditory environment, speeding up the automatic detection response.

While these patterns are consistent, they do not prove that sound processing differences or anxiety actually cause stuttering. “The study included a relatively modest sample size and used a cross-sectional design,” Şimşek said. “Therefore, the findings show associations rather than cause-and-effect relationships.”

“We cannot determine whether anxiety influences neurophysiological processing, whether neurophysiological differences contribute to anxiety, or whether both are influenced by other factors,” Şimşek said. He added that larger longitudinal studies will be necessary to clarify these relationships.

The study has a few other limitations that provide avenues for future research. The experiment relied on simple, pure tones rather than actual human speech sounds. Testing participants with spoken syllables or words might provide a more realistic picture of how the brain processes language during conversation.

The sample only included adults under the age of 45. Studying children, teenagers, or older adults could help scientists understand how these brain wave patterns change over a person’s lifespan. Additionally, the researcher excluded individuals with diagnosed psychiatric disorders, relying entirely on self-reported medical histories.

Methodologically, the raw electrical data from the brain scans was not retained after the specific wave peaks were extracted. Keeping the full datasets in future studies would allow scientists to conduct deeper, more advanced analyses of the brain signals. The study also did not apply formal statistical corrections for multiple comparisons, meaning a small portion of the statistical findings could be the result of random chance.

Future research might track individuals over several years or measure brain waves before and after speech therapy. “Our long-term goal is to better understand how neurophysiological and emotional factors interact in stuttering across the lifespan,” Şimşek said. “Future studies will investigate whether these brain responses change following speech therapy and whether they can serve as markers of treatment outcomes.”

He noted an interest in examining these relationships in different age groups and clinical populations. “Stuttering affects millions of people worldwide, yet misconceptions remain common,” Şimşek said. “Research often focuses on speech symptoms alone, but our findings suggest that sensory processing and emotional experiences are also important parts of the picture.”

“A more comprehensive understanding of stuttering may ultimately help clinicians develop more individualized and effective approaches to assessment and intervention,” Şimşek said. Identifying how these sensory and emotional pieces fit together could lead to more comprehensive treatments that address the entire nervous system.

The study, “Anxiety and Neurophysiological Correlates of Stuttering Severity in Adults Who Stutter,” was authored by Agit Şimşek.