Tone variation in Tswana-speaking individuals : the effect of voice disorders

Abstract

Introduction: Bantu languages, such as Tswana, are tone languages which use syllabic tone variation to convey word meaning. Vocal pathologies may affect vocal fold control that is required to vary syllabic tone. A person with a voice disorder could therefore be misperceived due to inability to effectively vary tone. Aim: To develop and validate a Tswana minimal pair word list for the assessment of tone production and tone perception, and to determine whether a voice disorder in a first language (L1) Tswana-speaker influences the accuracy of tone perception by typical L1 Tswana-speaking individuals. Method: A word list of 45 Tswana words, with accompanying pictures and sentences were compiled and validated by means of three pilot studies. Based on the results of the pilot studies the word list was narrowed down to 16 minimal pairs. Data were collected from a control group (9 typical L1 Tswana-speaking individuals) and an experimental group (5 L1 Tswana-speaking individuals with voice disorders). Participants from both groups produced the target words and a recording of each word production was judged by a listeners’ panel of five typical L1 Tswana-speaking judges. Results: Typical L1 Tswana listeners did not achieve 100% accuracy in a tone perception task. The mean scores of the control speakers ranged between 71% and 98%. The experimental group participants’ scores were lower although not significantly lower (p=0.109), ranging between 61% and 90%, compared to the scores of the control group. The experimental participant, who obtained the lowest mean score (61%), presented with a severe primary organic voice disorder. Conclusion: Not all typical speakers were able to produce word-level tone variation that makes word identification possible in a single-word context. Although no significant difference was found between the results of the two groups, indications are that a voice disorder could negatively impact syllabic tone variation.