The homogeneity of audibility and prosody of Zulu words for speech reception threshold (SRT) testing

The aim of this investigation was to determine which of 58 preselected Zulu words developed by Panday et al. (2007) could be used for Speech Reception Threshold (SRT) testing. To realize this aim the homogeneity of audibility of 58 bisyllabic Zulu low tone verbs was measured, followed by an analysis of the prosodic features of the selected words. The words were digitally recorded by a Zulu first language male speaker and presented at 6 intensity levels to 30 Zulu first language speakers (18-25 years, mean age of 21.5 years), whose hearing was normal. Homogeneity of audibility was determined by employing logistic regression analysis. Twenty eight words met the criterion of homogeneity of audibility. This was evidenced by a mean slope of 50% at 5.98%/dB. The prosodic features of the twenty eight words were further analyzed using a computerized speech laboratory system. The findings confirmed that the pitch contours of the words followed the prosodic pattern apparent within Zulu linguistic structure. Eighty nine percent of the Zulu verbs were found to have a difference in the pitch pattern between the two syllables i.e. the first syllable was low in pitch, while the second syllable was high in pitch. It emerged that the twenty eight words could be used for establishing SRT within a normal hearing Zulu speaking population. Further research within clinical populations is recommended.