Perceptual and acoustic predictors of speech intelligibility among Hebrew-speaking young adults with down syndrome

Background: Down syndrome (DS) is a common chromosomal disorder associated with various speech impairments, including reduced intelligibility. While speech subsystem deficits in DS have been documented, their relative influence on intelligibility remains understudied, particularly in non-English speaking populations. This study investigated speech intelligibility and select subsystem functioning in Hebrew-speaking young adults with DS, aiming to describe the speech production disorder and identify predictors of single-word intelligibility in this population. Methods: Twenty-four adults with DS and 24 typically developing (TD) peers produced common single words in Hebrew. Perceptual and acoustic analyses were conducted on select speech subsystems, including articulatory (consonant and vowel production) and phonatory measures. Results: Speakers with DS had higher error rates for complex consonants and demonstrated vowel space centralization compared to TD peers. Group differences were observed in most acoustic vowel measures, with interactions with speaker gender, but only select acoustic voice measures. Stepwise regression analysis identified three significant predictors of single-word intelligibility in the DS group, namely Percentage of Consonants Correct (PCC), Jitter (ppq), and average ellipse size of vowel clusters within the acoustic vowel space. Conclusions: These findings highlight the complex nature of speech intelligibility deficits in individuals with DS, emphasizing both articulatory and phonatory contributing factors. The results also suggest potential cross-linguistic differences in subsystem contributions to intelligibility. Clinical implications include the need for comprehensive assessment and targeted interventions addressing multiple speech subsystems in this population.