Vocal Characteristics across English-Northern Sotho Bilingual Speakers: A Comparative Study.

Introduction: Bilinguals constitute a significant portion of speech-language pathologists' (SLPs) caseloads. Insight into the cross-linguistic effect on voice is needed to guide SLPs to make linguistically appropriate observations when working with heterogenous populations.

Method: Nineteen female English-Northern Sotho bilinguals performed three speech tasks (reading, picture description, and monologue) in each language. Acoustic analysis of mean fundamental frequency (f0), intensity, and articulation rate was conducted with Praat. A panel of blinded listeners reached consensus after independently reviewing the recordings during perceptual analysis of voice quality, resonance, and glottal attack.

Results: The following statistically significant differences were found across and within the languages: The mean f0 was 204.61 Hz in the Northern Sotho picture description yet 196.50 Hz in the English picture description. The mean intensity of reading in Northern Sotho was 66.38 dB whereas the mean intensity of reading in English was 65.09 dB. Articulation rate was 3.78 syllables/s in English passage reading and 3.41 syllables/s in Northern Sotho passage reading. Within English, passage reading elicited a significantly quicker articulation rate than the picture description (3.34 syllables/s) and monologue (3.46 syllables/s). Within Northern Sotho, mean f0 was 203.83 Hz in passage reading yet 191.11 Hz in the monologue. Perceptual voice quality, glottal attack, and resonance were comparable across languages.

Conclusion: Relationships between languages spoken, task performance, and vocal characteristics were observed in English-Northern Sotho bilingual females. SLPs must consider the interaction of language, task performance, and vocal characteristics when working with bilingual clients.