Adults who stutter experience differences in how their brains process sound, and these sensory differences tend to overlap in both stuttering severity and anxiety levels. Recent research published in BMC Psychology Evidence suggests that stuttering involves a complex interaction between sensory processing, emotional states, and speech production. The results of this study suggest that assessing both neurological and psychological factors may improve treatment for people who stutter.
Stuttering is usually understood as a communication disorder that interrupts the physical flow of speech. People who stutter often have involuntary repetitions, lengthening, or interruptions in their vocal expressions. Most treatment approaches focus primarily on the motor aspects of speaking, treating the condition as a problem with the muscles and nerves that control the vocal cords, tongue, and lips.
Ajit Simsek, an assistant professor in the Department of Speech and Language Therapy at İnönü University in Malatya, Turkey, designed a study to investigate whether factors other than movement also contribute to developmental stuttering. “Stuttering has traditionally been thought of as primarily a motor speech disorder,” says Simszek. “However, increasing evidence suggests that auditory processing and emotional factors may also play an important role in clinical symptoms.”
Simsek, who is also the author of this book. A holistic perspective on stutteringI wanted to look beyond the physical mechanics of audio. “As a speech-language pathologist and researcher, I have long been interested in understanding stuttering from a broader perspective,” said Simshek. “This study aims to examine how neurophysiological processes and anxiety levels in adults who stutter are related to stuttering severity.”
Previous research suggests that people who stutter may process sounds differently in their brains. Auditory processing refers to how the brain perceives, interprets, and responds to sounds coming through the ears. This processing is highly relevant to speech fluency, as humans rely on auditory feedback loops to monitor and adjust their voices during conversations.
By combining electroencephalogram measurements and psychological evaluation, the authors aimed to uncover the broader neurological and emotional context of communication disorders. “One of the key messages is that stuttering is much more complex than just being ‘stuck for words,'” Simshek said. “Our findings suggest that adults who stutter have differences in how their brains process auditory information and report higher levels of anxiety than fluent speakers.”
He noted that these results support the view that language, brain function, and emotional experience interact 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 language disorders. All participants were between the ages of 18 and 45.
To ensure a fair and balanced comparison, the two groups were matched based on age, education, and biological sex. Simsek confirmed that all participants had normal hearing through standard hearing tests. They also ensured that all participants were right-handed, as handedness can affect which side of the brain processes language tasks.
A certified speech-language pathologist evaluated the stuttering group using a standardized severity assessment tool to determine whether symptoms were mild, moderate, or severe. To measure emotional state, participants completed a standardized questionnaire that assessed both immediate anxiety and long-term anxiety tendencies. Immediate anxiety refers to how a person feels at the moment, while long-term anxiety refers to a person’s general personality traits.
To assess brain activity, researchers used electroencephalograms. This non-invasive tool involves placing small sensors on the scalp to record electrical signals, often called brain waves. The researchers focused specifically on event-related potentials, which are the distinct electrical spikes and dips that occur in the brain milliseconds after a person hears a sound.
In 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 device recorded the precise timing and electrical intensity of the brain’s response to each sound.
The study tracked early brain wave responses that mark the exact moment the sound reaches the brain’s auditory cortex. We also tracked subsequent reactions. This reflects how your brain integrates that sound and prepares you to respond to it both sensory and physical.
In the second part of the experiment, participants completed a passive listening test designed to measure automatic auditory change detection. They heard 500 tones, 80 percent of which were standard 1000 hertz tones. The remaining 20% were slightly higher pitched tones played at 1200 hertz.
This unpredictable change triggers certain automatic brainwave responses when the brain notices unexpected changes in the environment. Compared to controls, adults who stutter showed slower EEG responses and smaller physical size on nearly every measure. It took even longer for their brains to recognize the sounds.
Furthermore, the electrical strength of the responses was generally weaker than in those who did not stutter. These differences in brain waves were closely related to the severity of a person’s stuttering. Participants with severe stuttering had the slowest and diminished responses during the early and middle stages of speech processing.
As the severity of stuttering increased from mild to moderate to severe, the brain’s processing speed and electrical response strength decreased progressively. Psychological measurements have shown that adults who stutter experience significantly higher levels of both immediate and general anxiety. Similar to EEG patterns, anxiety scores also increased with stuttering severity.
People 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,” Simshek said. “We observed that people with more severe stuttering tended to show greater changes in auditory cortical responses and higher anxiety scores.”
This pattern, he explained, supports the idea that stuttering is a multifaceted symptom and not just a speech motor disorder. Interestingly, brain waves associated with detecting unexpected sound changes showed a unique pattern in people with severe stuttering. Overall, the stuttering group was less responsive to sound changes than the control group, but the severe stuttering group responded faster and more intensely to unexpected sounds than the mild stuttering group.
Researchers suggest that this heightened response to unexpected sounds may be related to heightened anxiety. High anxiety can cause your nervous system to become hypersensitive. This state of high alertness can make the brain hypersensitive to sudden changes in the auditory environment, leading to faster automatic detection responses.
Although these patterns are consistent, they do not prove that differences in speech processing or anxiety actually cause stuttering. “This study included a relatively modest sample size and used a cross-sectional design,” Simsek said. “Thus, this finding indicates an association rather than a causal relationship.”
“We cannot determine whether anxiety affects neurophysiological processing, whether neurophysiological differences contribute to anxiety, or whether both are influenced by other factors,” Simszek said. He added that larger longitudinal studies are needed to clarify these relationships.
This study has several other limitations that provide avenues for future research. This experiment relied on simple, pure sounds rather than actual human speech. Testing participants on audio syllables and words could provide a more realistic picture of how the brain processes language during conversation.
The sample included only adults under 45 years of age. Studying children, teens, or older adults could help scientists understand how these brainwave patterns change over a person’s lifetime. Additionally, researchers relied entirely on self-reported medical history and excluded individuals diagnosed with mental disorders.
Methodologically, the raw electrical data from the brain scans was not retained after the peaks of a particular wave were extracted. Preserving the complete data set for future studies will allow scientists to perform deeper and more sophisticated analyzes of brain signals. Also, because no formal statistical correction for multiple comparisons was applied in this study, a small portion of the statistical findings may be due to chance.
Future studies could track individuals over several years and measure their 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,” Simshek said. “Future studies will investigate whether these brain responses change after speech therapy and whether they serve as markers of treatment outcome.”
He noted that he would be interested in examining these relationships in different age groups and clinical populations. “Stuttering affects millions of people around the world, but misconceptions remain common,” Simszek said. “While research often focuses solely on language symptoms, our findings suggest that sensory processing and emotional experience 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,” Simshek said. Identifying how these sensory and emotional parts 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.
