Acoustic properties of fricatives /s/ and /∫/ produced by speakers with apraxia of speech: Preliminary findings from Arabic

Abstract This study examines the acoustic characteristics of fricatives in Arabic-speaking individuals with apraxia of speech (AOS), contributing to cross-linguistic research on motor speech disorders in under-studied languages, such as Arabic. Participants included two Palestinian Arabic speakers with AOS and two healthy controls, each producing 120 repetitions of word-initial /s/ and /ʃ/ followed by long vowels (/a:, u:, i:/). Acoustic analyses focused on fricative duration, formant frequencies (F1 and F2), intensity, the center of gravity (M1), and spectral moments for the fricatives. In contrast to previous findings, AOS speakers in this study exhibited significantly longer segment durations, lower intensity contrast between vowels and fricatives, and reduced spectral distinctiveness of /s/ and /ʃ/ compared to controls. These findings also provide further evidence that M1 is an effective metric for identifying misarticulations in fricatives in AOS. Interestingly, although AOS speakers showed higher formant values, they still produced distinct vowel categories. Together, these results suggest that AOS broadly impacts articulation in Arabic speakers, while vowel production remains relatively preserved – a pattern inconsistent with some previous studies. Clinically, these results highlight potential diagnostic markers for AOS in Arabic-speaking populations. However, given the small sample size, further research is needed to validate these findings and explore AOS characteristics across larger Arabic-speaking groups.