Perceptions of audible nasal emission in speakers with cleft palate: A comparative study of listener judgments

Objective: Audible nasal emission is a common speech distortion observed in persons with cleft palate. This study examined the validity and reliability of perceptual judgments of audible nasal emission using interval scaling and magnitude estimation techniques. Participants: Speech samples were collected from six adolescents with repaired cleft palate, all of whom demonstrated audible nasal emission. A total of 31 adults performed rating tasks in which they judged the severity of audible nasal emission in speech samples. Measures: Occurrences of audible nasal emission in speech samples were identified using visual and auditory inspection. Using an acoustic modification technique, samples were digitally modified to amplify perceived occurrences of audible nasal emission to create three stimulus conditions. The original recording of the speech samples served as a control condition. The severity of audible nasal emission in the samples was judged by multiple listeners using interval scaling and magnitude estimation without a modulus. Statistical analysis included analysis of variance, regression, and curve-fitting methods. Results: Magnitude-estimation ratings demonstrated stronger evidence of validity and reliability than interval scaling. A curvilinear relationship was found between the sets of ratings. Conclusions: The results of this study suggest that audible nasal emission may be a prothetic or ratio-level perceptual continua. Listeners should consider using magnitude estimation or other ratio-based methods for perceptual judgments of audible nasal emission.