Date of Defense

4-16-2015

Date of Graduation

5-2015

Department

Speech Pathology and Audiology

First Advisor

Helen Sharp

Second Advisor

Stephen Tasko

Third Advisor

Gregory Flamme

Abstract

Background. Vowels are a commonly used stimulus for evaluating speech resonance because hypernasality is best detected in vowel sounds. It was observed that steady-state sustained vowels show considerable within sample nasalance variance, although nasalance is expected to be stable for this speech target.

Purpose. The purpose of the study was to ascertain the prevalence of variability among normal speakers in steady state vowel nasalance traces and to determine the variables that predict variability.

Methods: Sixty-one participants aged 18 through 30 years were recruited. All participants were lifelong residents of the lower peninsula of Michigan with normal hearing sensitivity and no history of cleft palate. Nasalance was measured using the KayPentax Nasometer II 6450 for nasometry paragraphs, sentences, repeated CV syllables, and sustained vowels presented in random order. Variability in nasalance was evaluated for 1411 steady state vowel productions. Presence of variability was identified using standard deviation around mean nasalance and nasalance distance (maximum nasalance – minimum nasalance). All nasalance measures were transformed to rationalized arcsine units (RAU) to allow for statistical analyses of percentage data. Variables considered included individual speaker, gender, trial, vowel produced, speaker fundamental frequency, laryngeal periodicity, and signal intensity.

Results: Nearly all (92%) samples had a standard deviation around mean nasalance greater than 5%, showing greater variance than expected. Half of all vowels produced had a within sample minimum to maximum nasalance distance of at least 19% or greater, also demonstrating larger than expected variance. No significant relationship was found between within sample variation and trial, fundamental, frequency, periodicity, or gender. However, speaker, vowel, and vocal intensity were significantly related to likelihood of variability of nasalance within steady state vowel productions.

Discussion: Variation in nasalance is common in a sample of 61 healthy adult volunteers, with half of all vowels produced with a nasalance distance of 19% or greater. It is expected that variation would be more likely in clinical populations of children and those with velopharyngeal or neuromotor dysfunction. Instability of nasalance traces within steady state speech production raises concerns about interpretation of nasalance measures in clinical and research settings.

Conclusion: Sustained vowels should be considered an unreliable stimuli for measuring nasalance. Further research is needed to understand the reason for unstable nasalance in sustained vowel productions.

Access Setting

Honors Thesis-Open Access

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