# The Link Between Syntactic Complexity and Stuttering‐Like Disfluencies in French Speaking Adults

## TL;DR

This study finds that more complex sentences lead to more stuttering-like disfluencies in adults who stutter, with sentence length being a key factor.

## Contribution

The study introduces MLU as a clinically useful measure for predicting disfluencies in adults who stutter.

## Key findings

- Adults who stutter produce more disfluencies as syntactic complexity increases.
- MLU is the most effective measure for predicting disfluency rates in adults who stutter.
- Severe stutterers show higher disfluency rates than mild or moderate ones.

## Abstract

Stuttering is a neurodevelopmental disorder characterized by speech disfluencies. While studies have shown a link between syntactic complexity and stuttering in children, its role in adults who stutter (AWS) remains unclear. This study investigates whether increased syntactic complexity correlates with stuttering‐like disfluencies (SLDs) in AWS and evaluates three syntactic complexity indices.

Participants included 24 French‐speaking adults (12 AWS, 12 controls), matched for age, gender, and education. Participants completed a sentence description task using sentences of varying syntactic complexity. Syntactic complexity was quantified using three measures: Mean Length of Utterance (MLU), Index of Syntactic Complexity (ISC), and Index of Productive Syntax (IPSyn). Disfluencies were categorized as SLDs or other disfluencies (ODs). Statistical analyses examined the relationship between syntactic complexity and disfluencies across participant groups.

AWS produced significantly more SLDs than controls across all levels of syntactic complexity. The number of disfluencies increased with syntactic complexity in AWS but not in controls. MLU was the most sensitive index for predicting disfluencies. Severe stutterers exhibited higher disfluency rates compared to mild and moderate stutterers.

Increased syntactic complexity exacerbates stuttering in AWS. MLU, a measure of sentence length, proved most effective for explaining disfluency rates, suggesting its clinical utility. Findings support the demands and capacities model, indicating that reducing syntactic demands may alleviate stuttering.

What is already known on this subject
Persistent developmental stuttering is characterized, among others, by an increased number of disfluencies, known as stuttering‐like disfluencies. Many linguistic factors influence the apparition of stuttering‐like disfluencies, such as phonological characteristics of disfluent sounds. Regarding morphosyntactic factors, it is known that disfluencies switch from function to content words in adults and studies on some languages show that syntactic complexity does influence stuttering in the adult population. However, such studies use different measures of syntactic complexity and are scarce for French.
What this paper adds to existing knowledge
In our study, we tested a protocol designed to explore syntactic complexity and its relationship with stuttering. Disfluencies were elicited during speech production across varying levels of complexity, and three different measures were used to address the research question. Among these, MLU proved to be the most effective in explaining the occurrence of stuttering‐like disfluencies, confirming that sentence length plays a more significant role than sentence structure in adults who stutter.
What are the potential or actual clinical implications of this work?
This study highlights the importance of syntactic complexity in stuttering, offering insights for clinical speech therapy and research. While stuttering therapy often focuses on children, these findings suggest that simplifying sentence production could also benefit adults who stutter. Speech therapists could work on improving the linguistic abilities of PWS, particularly syntax, to reduce disfluencies and build a stronger language foundation. The study also validates MLU as a reliable tool for measuring disfluencies, easily applicable in clinical practice. Combining these insights with existing programs, such as the Camperdown program, could enhance treatment by addressing both speech fluency and disorder awareness.

Persistent developmental stuttering is characterized, among others, by an increased number of disfluencies, known as stuttering‐like disfluencies. Many linguistic factors influence the apparition of stuttering‐like disfluencies, such as phonological characteristics of disfluent sounds. Regarding morphosyntactic factors, it is known that disfluencies switch from function to content words in adults and studies on some languages show that syntactic complexity does influence stuttering in the adult population. However, such studies use different measures of syntactic complexity and are scarce for French.

In our study, we tested a protocol designed to explore syntactic complexity and its relationship with stuttering. Disfluencies were elicited during speech production across varying levels of complexity, and three different measures were used to address the research question. Among these, MLU proved to be the most effective in explaining the occurrence of stuttering‐like disfluencies, confirming that sentence length plays a more significant role than sentence structure in adults who stutter.

This study highlights the importance of syntactic complexity in stuttering, offering insights for clinical speech therapy and research. While stuttering therapy often focuses on children, these findings suggest that simplifying sentence production could also benefit adults who stutter. Speech therapists could work on improving the linguistic abilities of PWS, particularly syntax, to reduce disfluencies and build a stronger language foundation. The study also validates MLU as a reliable tool for measuring disfluencies, easily applicable in clinical practice. Combining these insights with existing programs, such as the Camperdown program, could enhance treatment by addressing both speech fluency and disorder awareness.