Speech disfluency characteristics among Japanese adults who stutter and clutter and fluent speakers
2College of Education, Ibaraki University, Japan
3Department of Otorhinolaryngology, Head and Neck Surgery, Keio University School of Medicine, Japan
4Kusunoki Dental Clinic, Shiyuukai Medical Corporation, Japan
5Department of Rehabilitation, Tsukuba Memorial Hospital, Japan
Purpose: Stuttering and cluttering are fluency disorders with distinct and overlapping speech characteristics. However, detailed speech disfluencies in stuttering and cluttering remain underexplored. This study aimed to investigate speech disfluencies among Japanese adults who stutter (AWS), clutter (AWC), or not stutter and clutter (Control).
Methods: Speech samples with multiple speech tasks were collected from 50 participants self-identifying as having a fluency disorder and 25 participants who do not. Participants were classified using Tomisato et al.`s (2024) provisional criteria, where cluttering is defined as both a disfluency ratio (normal disfluencies/stuttering-like disfluencies) greater than 1.2 and a mean articulatory rate greater than 7.5 in a monologue task.
Results: Of the 50 fluency-disordered participants, 25 were classified as cluttering, and 25 as stuttering. The mean (SD) rate of stuttering-like disfluencies per 100 speech units was 14.4 (16.7) in AWS, 5.9 (5.2) in AWC, and 0.6 (1.0) in Controls. Stuttering-like disfluencies were significantly higher in AWS (Z= 32.8, p<.001, nonparametric test) and AWC (Z= 26.6, p<.001) compared to Controls, but no significant difference was found between AWS and AWC (Z= 6.14, p =.939, Bonferroni correction). Normal disfluencies averaged 23.1(9.7), 24.4(8.2), and 15.3(7.2) for AWS, AWC, and Controls, respectively. Control participants exhibited significantly lower disfluencies than both AWS and AWC, but no significant difference emerged between AWS and AWC. Trends were consistent across other speech tasks, with minor variations.
Discussions: While overall disfluency rates were similar between AWS and AWC, stuttering-like disfluencies differed to some extent. Variability in disfluency type (e.g., repetition, block, or interjection), task-specific differences (e,g, monologue, oral reading, or other speech tasks), and articulation rate variability may influence perceived differences between stuttering and cluttering.
Reference: Tomisato, S., Mori, T., Asano, K., Iimura, D., Yada, Y., Takahashi, S., Wasano, K., Kono, T., Ozawa H. (2024). Speech characteristics that differentiate stuttering and cluttering in Japanese speakers. Frontiers in Psychology, 15, 1408929.