The Impact of Clear and Loud Speech Cues on Acoustic and Perceptual Features of Speech Production in Adolescents With Down Syndrome

Purpose: There are few evidence-based speech interventions designed to alter speech production in a way that ultimately results in increased speech intellig-ibility in adolescents with Down syndrome (DS). The primary purpose of this study was to examine the impact of clear and loud speech cues on acoustic and perceptual features of speech production in adolescents with DS. Method: Eight adolescents diagnosed with DS repeated sentences of varying lengths in three conditions: habitual, big mouth (i.e., clear speech), and strong voice (i.e., loud speech). Four hundred eighty adult listeners (20 listeners per adolescent per condition) provided orthographic transcriptions of adolescent’s speech, which were used to calculate intelligibility scores. Acoustic measures of speech rate, articulation rate, proportion of time spent pausing, vocal intensity, and fundamental frequency were calculated for each sentence. Results: The big mouth condition resulted in significantly increased intelligibility, slowed speech and articulation rates, increased pauses, increased vocal intensity, and increased fundamental frequency. The strong voice condition resulted in signif-icantly increased vocal intensity and fundamental frequency, but no other changes. Speech rate was the only variable that explained any of the variance in intelligibility. Conclusions: Adolescents with DS respond differently to clear and loud speech cues. In particular, clear speech cues resulted in significant increases in intellig-ibility, but loud speech cues did not. Clear speech cues hold promise as an intervention strategy for adolescents with DS.