The development of a Zulu speech reception threshold test for Zulu first language speakers in KwaZulu-Natal (KZN).

Abstract

The measurement of speech reception threshold (SRT) is best evaluated in an individual's first language. Currently there is a paucity of linguistically matched materials to measure the SRT of Zulu First Language Speakers (ZFLS) in Kwa Zulu-Natal (KZN). Therefore, the present study focused on developing and assessing a Zulu SRT word list for Zulu First language Speakers (ZFLS) in KZN, according to adapted criteria for SRT in Zulu. In addition, the application of the developed list was evaluated. The study therefore followed a two phase methodological framework. Phase one focused on the development and assessment of the word list. Phase two focused on the application of the word list in a normal hearing population from KZN. Phase one of the study was realized within a descriptive survey design and Phase two was realized using a within- participant quasi experimental design. Phase one included aims one and two of the study. Phase two included aim three of the study. However, each aim had several objectives which were realized consecutively. For aim one of the study, three objectives were achieved i.e. for objective one, 131 common bisyllabic words were identified by two Zulu speaking language interpreters and two tertiary educators. Eighty two percent of these words were described as bisyllabic verbs. The outcome of objective two concluded that 58 bisyllabic verbs were rated as being familiar, phonetically dissimilar and low tone verbs by five linguistic experts, using a three point Likert scale. The agreement among the raters was generally good for each criterion, according to the Kendall's co-efficient of concordance at 95% level of confidence. Two objectives were generated to realize aim two of the study. These included, the measurement of homogeneity of audibility of the 58 words selected in aim one and the acoustic analysis of the words. The findings for the homogeneity of audibility were based on a logistic regression analysis. Thirty normal hearing adult ZFLS (18-25 years) participated in this aim of the study. The mean slope of 50% for 28 words was 5.98%/dB. Therefore, 28 words were measured as being most homogenous. The 28 words were also assessed acoustically. The acoustic analysis indicated that the pitch contours confirm the prosodic pattern of the words selected in terms of Zulu linguistic structure, as the majority of the verbs (89%) indicated a difference in the pitch pattern between the two syllables. Furthermore, trends were noted with regard to the energy contours. The acoustical analysis supports the findings of objective one of aim two. For aim three of the study, twenty six normal hearing adult ZFLS, with functional proficiency in English were assessed. The SRT was measured using the developed Zulu SRT word list. In addition, the SRT was measured using the original CIDW2 list. The Pearson product moment correlation co-efficient was utilized for the measurement of the relationship between the SRT (Zulu) and the Pure Tone Average (PTA). Similarly, the Pearson product moment correlation between the SRT (English) and PTA was obtained. A good relationship between the SRT scores and PTA was reported when both lists were used. However, a stronger correlation between the Zulu SRT and PTA (r=.76) than with the English SRT and PTA (r=0.62) were noted. The results in aim one and aim two of the study highlighted the importance of adapting the criteria for SRT to suit the structure of the language. Aim three confirmed this premise as the implication of a stronger correlation may be related to the familiarity of the stimuli to the Zulu First Language Speaker. The study therefore contributed to both research and clinical implications. Some of the important research implications for the study include: the application of the Zulu SRT word list to a varied clinical population with a hearing disorder or loss, the standardization of the developed Zulu SRT word list on a larger sample, the development of SRT materials in other African languages in South Africa. Important clinical implications of the study include that the findings in the study support the need for speech material to be appropriate to the language of the client and the developed SRT word list in Zulu is applicable to adult ZFLS in KZN.