Effects of hoarseness on ratings of hypernasality -source-filter-theory approach-

Abstract

The effects of hoarseness on ratings of hypernasality were examined by the perceptual experiment using synthesized stimuli. Twenty-four kinds of stimuli were synthesized by combining 6 sources (normal, moderate roughness, and severe roughness × 2 (/a/,/i/)), and 4 filters (severe hypernasality and normalx2 (/a/,/i/)), based on source-filter theory. Four experienced speech pathologists rated the severity of hypernasality of the stimuli using a 5-point equal-appearing interval scale. Results revealed that severely rough voices were rated lower in hypernasality than normal or moderately rough voices, especially for severe hypernasal filters. Moderately rough voices were rated differently depending on kinds of filter. Acoustical analysis suggested that some spectral changes to the stimuli caused by roughness result in changes in perceived hypernasality. Clinical issues pertaining to these follow-up investigations are discussed, and future works are suggested.