The need for a standard approach for the diagnosis of speech disorders, in particular resonance disorders associated with cleft lip and/or palate, has been recognised. A reliable and valid measure of nasality is important, because it not only affects clinical decision making but is also essential for the evaluation of treatment outcomes. In order to allow cross-linguistic comparisons of the assessment of resonance, language specific stimuli developed according to a common set of guidelines have been recommended. The aim of this thesis was to contribute to the development of an assessment protocol for use in Malay speaking individuals with clefts of the lip and/or palate, specifically focusing on the detection of nasality. A series of four studies were completed which systematically developed and then validated a set of stimuli in the Malay language using both perceptual and instrumental measures. / In the first study, three stimuli were developed for the assessment of nasality based on both the proportion of nasal phonemes in typical conversation samples in Malay and guidelines from the current international literature. The phonetic content of the stimuli were comparable to similar passages used in English and comprised of an Oral Passage, a Nasal Passage and a Set of Sentences. / In the second study, the stimuli constructed were tested in a large number of typically developing (non-cleft) Malay speaking children using both instrumental and perceptual methods of assessment. The results of this study provide the first set of normative data of nasalance scores for the three newly developed stimuli. The mean nasalance score for the Oral Passage was 13.86% (SD = 5.11, 95% CI = 13.04–14.68), 60.28% (SD = 6.99, 95% CI = 59.15–61.41) for the Nasal Passage, and 27.72% (SD = 4.74, 95% CI = 26.96–28.49) for the Set of Sentences. These scores were significantly different from each other suggesting that they can be used to detect the different types of resonance disorder in speech (e.g. hypernasality and/or hyponasality). / In the third study, the stimuli were validated in a sample of Malay speaking children with cleft of the lip and/or palate and compared with a control population. Nasality was measured using perceptual evaluation and nasometry. The results suggested that the Oral Passage and Set of Sentences developed in Malay were valid measures for detecting hypernasality for both perceptual evaluation of nasality, and for nasometry. Due to the small number of participants that were hyponasal, the validity of the Nasal Passage could not be determined. / For nasometry to be clinically relevant threshold values that indicate abnormal nasality are required. The threshold values for each of the stimuli were first ascertained after obtaining typical nasality levels from a group of healthy Malay speaking children and then tested in a sample of cleft and non-cleft Malay speaking children. In contrast to the nasalance cutoffs obtained from typical Malay speaking children, the cutoffs obtained from the cleft children yielded better outcomes for detecting resonance disorders. The cutoffs were: ≥ 22% for the Oral Passage (sensitivity = 0.91, specificity = 0.93, overall efficiency = 0.92), ≥ 30% for the Set of Sentences (sensitivity = 0.96, specificity = 0.85, overall efficiency = 0.88) and ≤ 39 on the Nasal Passage (sensitivity = 1.00, specificity = 0.99, overall efficiency = 0.99). / Finally, the fourth study explored the application of recently developed techniques for assessing nasality using spectral voice analysis and compared these results with nasometry using a sub-sample of Malay speaking children from the third study. The participants were children with cleft lip and/or palate with perceived hypernasality and a group of healthy controls perceived to have normal resonance. The potential of assessing nasality using vowels, which ideally can be an easier option to administer clinically and have minimal impact on language and literacy skills, were investigated. / The findings showed that only the one-third-octave analysis method could be successfully used to detect hypernasality in the cleft population compared to the VLHR method. Using the one-third-octave analysis, the spectral characteristics of nasalised vowel /i/ taken from /pit/ and /tip/ showed an increase in amplitude in F1, between F1 and F2 regions. The amplitude of the formants at F3 region was lower in the cleft group but did not differ from the control group as reported in previous studies. Although, the one-third-octave analysis has some potential in detecting hypernasality, the accuracy of the analysis compared to perceptual ratings of nasality was only moderate. Compared to nasometry, the diagnostic value of the one-third-octave analysis in detecting hypernasality was lower. / The overall findings suggest that, except for the Nasal Passage, the Oral Passage and the Set of Sentences developed in Malay using this systematic approach were culturally appropriate and valid for the assessment of nasality. Furthermore, by comparing two instrumental methods (nasometry and spectral analysis) with perceptual evaluation in a large number of cleft and typically developing children, the present thesis was able to demonstrate the clinical benefits of two recently proposed methods of spectral voice analyses and compare them to existing methods. Compared to spectral analysis, nasometry remains a superior method for assessing nasality. Threshold values that indicate abnormal nasality levels for the newly developed stimuli in Malay have been recommended.
| Identifer | oai:union.ndltd.org:ADTP/269926 |
| Date | January 2009 |
| Creators | Mohd Ibrahim, Hasherah |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Restricted Access: Abstract and Citation Only Available |
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