Abstract:
This study investigated the relationship between specific acoustic features and perceptual judgment of speech intelligibility of Mandarin-speaking young adults with cerebral palsy. Use of the minimum phonetic contrast task allowed for intelligibility analysis and correlated acoustic analysis according to specific articulators spatial and temporal movements. Selected task contrasts included vowel height, vowel frontness, aspiration--unaspiration, affricate--fricative, stop--nasal, nasal, and stop articulation place. Speech materials consisted of 90 bisyllabic words. Perceptual judgments from item identification and scaling procedures reflected the diversity of speech intelligibility in 20 cerebral-palsied adults. Vowel contrasts yielded higher perceptual accuracy than consonant. All phonetic contrasts correlated well with speech intelligibility. However, multiple regression analysis revealed that three contrasts (aspiration--unaspiration, affricate--fricative, and vowel frontness) accounted for 99% intelligibility variability. Seven acoustic parameters were examined; they were F1, F2-F1, VOT, frication duration, percentage of burst appearance, nasal characteristic, and burst spectrum. F1, F2-F1, nasal characteristic, and burst spectrum were found to differentiate the cerebral-palsied subjects from the normal speakers. Results from multiple regression predicted intelligibility scores with 74.8% accuracy by acoustic parameters related to F2-F1, VOT, and percentage of burst appearance. These findings are discussed in relation to specific areas of production deficiency in the cerebral-palsied population.