Phonetic Intelligibility Testing in Developmental Motor Speech Disorders: a Preliminary Tool in Hebrew

Background: Speech intelligibility is a core outcome in the assessment and treatment of individuals with developmental motor speech disorders. While open-set intelligibility testing is widely used, a closed-set phonetic intelligibility assessment, which evaluates listener perception of systematically varied speech contrasts, offers a focused approach to identifying segmental errors that impact intelligibility. However, such tools are unavailable in Hebrew. Aims: This study introduces a novel, preliminary closed-set phonetic intelligibility tool designed for Hebrew speakers with development motor speech disorders, examining its utility in identifying phonetic contrasts produced in error by speakers with Down syndrome (DS), and determining overall error profiles of contrast categories. Methods and Procedures: Recordings from 23 Hebrew-speaking adults with DS, between the ages of 21 and 37 years, were analyzed using a closed-set intelligibility paradigm, wherein naïve listeners selected perceived words from contrast-based minimal pairs. Error rates were calculated for individual phonetic contrasts and contrast categories (voicing, place, manner, vowels, and syllable structure). Closed-set intelligibility assessment scores were compared with those of open-set assessments, and phonetic profiles of individual contrasts and categories were formed across speakers. Outcomes and Results: Closed-set intelligibility scores were higher than open-set transcription accuracy scores. Voicing contrasts, particularly in coda position, were most frequently impaired and significantly correlated with closed-set intelligibility scores. The overall contrast-category profile of the speakers with DS demonstrated voice, place, and manner difficulties across speakers, with only minimal vowel errors. Conclusions and Implications: The Hebrew closed-set intelligibility tool successfully identified contrast-specific deficits relevant to speech intelligibility in speakers with DS. Its potential clinical value lies in targeting intelligibility-reducing features with increased diagnostic precision and language-specific relevance. WHAT THIS PAPER ADDS: What is already known on this subject Closed-set phonetic intelligibility testing may facilitate the identification of errors that impact speech intelligibility among individuals with motor speech disorders. However, such testing is limited in languages other than English. What this study adds to existing knowledge The preliminary closed-set intelligibility tool in Hebrew identified phonetic contrasts that were related to speech intelligibility scores among speakers with Down syndrome. Voicing errors were most consistently associated with reduced speech intelligibility among speakers. What are the potential or actual clinical implications of this work? Language-specific tools are necessary for determining key factors affecting speech intelligibility among speakers with motor speech disorders. Furthermore, cross-linguistic factors may differentially affect phonetic contrasts that are associated with reduced speech intelligibility.