The effect of voice disorders on lexical tone variation: Exploratory study in an African language

Purpose: The aim was to determine if the presence of a voice disorder in speakers of Setswana, an African tone language, will negatively impact the accuracy of identification by typical first language judges of words belonging to tonal minimal pairs.Method: A quasi-experimental between-group comparison and individual case studies were conducted. Five participants with different types and degrees of voice disorders and nine control participants produced 10 tonal minimal word pairs. Five judges had to identify which of a pair was produced.Result: The mean scores of the control and experimental speakers as groups differed, but the difference was not statistically significant. Control participants scored between 19.6/20 and 14.2/20 words correctly identified. Individual data revealed that four of the nine control participants attained at least one perfect score across judges and six had mean scores of 18.0/20 and higher. The highest scoring experimental participant, presenting with a mild voice disorder, attained a mean of 18.0/20. The lowest scoring participant, presenting with the most severe dysphonia, had a mean of 12.2/20 words correctly identified.Conclusion: These preliminary results appear to suggest that a severe voice disorder could compromise lexical tone variation and by implication the intelligibility of a message.