Acoustic Variability in the Fluent Connected Speech of Adults who Stutter

Abstract

Previous research has investigated acoustic and perceptual comparisons between the fluent speech of adults who stutter (AWS) and adults who do not stutter (ANS). Numerous studies demonstrate differences in temporal and frequency-related characteristics of the fluent speech of AWS. For example, the literature has suggested that the fluent speech of AWS is characterized by an increased number of pauses, increased voice onset time, centralized vowel space, reduced F2 transitions, reduced variability in fundamental frequency, longer segment durations, and reduced articulation rate. However, findings are mixed overall and there is a large degree of heterogeneity in methodologies employed by these studies. Furthermore, most of this literature is based on vowels, syllables, words and phrases with limited research on variability in the connected speech of AWS. The current study compared the fluent speech samples of 3 AWS with sex- and age-matched ANS. Four different connected speech tasks were investigated: recitation, reading, monologue, and conversation. Using a schema to define typical and atypical disfluencies, researchers removed stutter-like disfluencies from speech samples. Acoustic analyses measured speech and articulation rate, ratios of pause time to total time, of voiced time to total time, and of articulation time to total time, fundamental frequency (fo), fo range and coefficient of variation, sound pressure level range, cepstral peak prominence, vowel space area, and voice range density profile. There were no statistically significant group differences for any measure except for the ratio of pause time to total time, and no significant effect of speaking condition on any measure. This supports prior evidence (Few & Lingwall, 1972) that AWS do not experience increased pause time when compared to fluent controls. Findings loosely suggest that fluent connected speech of AWS does not differ significantly from that of ANS in terms of acoustic characteristics related to rate, intensity, and frequency.