Evaluation of nasal speech a study of assessments by speech-language pathologists, untrained listeners and nasometry
Abstract: Excessive nasal resonance in speech (hypernasality) is a disorder which may have negative communicative and social consequences for the speaker. Excessive nasal resonance is often associated with cleft lip and palate, velopharyngeal impairment, dysarthria or hearing impairment. Evaluation of hypernasality has proved to be a challenge in the clinic and in research. There are questions regarding the accuracy and reliability of auditory perceptual evaluations of nasal speech, and whether instrumental measures can be used to improve the reliability of clinical evaluation. There is also the question of whether clinical evaluation reflects the impact of hypernasality in a speaker’s everyday life.The purpose of this thesis was to evaluate the extent of reliability problems connected with auditory perceptual assessment of nasality in speech, to explore whether they might interfere with treatment decisions or have an impact in the everyday life of patients, and whether they can be effectively diminished by the use of nasometry.Speakers with cleft lip and palate or velopharyngeal impairment formed the basis of the clinical population used in this study. Speech samples from 52 of these speakers, along with samples from a reference population of 21 speakers who did not have cleft palate, velopharyngeal impairment or speech disorders were used in perceptual evaluation tasks. Fourteen speakers from the clinical population and 11 from the reference population also underwent nasometric evaluation. A further reference population of 220 children from three Swedish cities, whose ages were consistent with those used for clinical checks of children born with cleft palate were assessed with nasometry to establish normative data for the Nasometer™. Perceptual speech assessments were conducted on hyper- and hyponasality, as well as audible nasal air emission and/or nasal turbulence, using 5-point ordinal scales. Listeners were SLPs experienced in the evaluation of cleft palate speech, non-expert SLPs and untrained listeners. Listening assessments were performed from audio recorded speech samples assembled in random order. Nasometry measures were made on three speech passages each with specific phonetic content, using the Nasometer™, model II.Perceptual evaluation Results showed that for hypernasality assessment, 15% of hypernasality assessments had disagreements between expert SLPs that were potentially important for clinical decisions, as did 6% of assessments for audible nasal air emission and/or nasal turbulence. For nasality problems, a comparison of expert and untrained listeners showed that they generally agreed on which speakers were hypernasal and on the ranking of nasal speakers. All speakers that had been rated with moderate to severe hypernasality by expert listeners were considered by the untrained listeners as having a serious enough speech disorder to call for intervention. However, in the case of audible nasal air emission and/or nasal turbulence the expert listeners were more prone to notice this feature than the untrained listeners.Instrumental evaluation The development of normative values for the three Swedish passages for the NasometerTM (comparable to normative values in other languages) has provided a basis for use of instrumental measures in Swedish clinics, oral sentences mixed sentences nasal sentences. The measures showed no significant differences due to city, gender or age within an age range of 4-10 years. When nasometry measures were compared with perceptual evaluation of speech samples from the same speakers, all correlations were moderate to good for expert SLPs and non-expert SLPs. The difference between correlations was significantly higher for expert SLPs than for untrained listeners.Reliability figures for perceptual assessments for expert SLP listeners indicated that there were some cases where lack of reliability could affect clinical decision making. However, in the main, judgements of nasality problems made by clinicians had everyday validity. They reflected the impressions of the everyday listener, especially in regard to the need for intervention. The study also indicates that now that Swedish norms are available, the Nasometer™ might be useful as a complement to auditory perceptual clinical speech assessments in Swedish cleft palate clinics in order to improve reliability of clinical assessment.
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