Acoustic measures of stutterers' and nonstutterers' fluency in two speech contexts.

The purpose of this study was to compare stutterers' and nonstutterers' fluency during multiple productions of two dissimilar speech contexts. Twenty-two adult stutterers were matched within 1 year of age to 22 nonstutterers. Spectrographic analyses were performed on subjects' five consecutively fluent productions of a simple isolated phrase and a phrase extracted from an oral reading passage. Measures of fluent voice onset time (VOT), and vowel, consonant, and total phrase durations were calculated from the five repetitions of each phrase. From the isolated phrase, there were a total of five fluent durational measures (i.e., one VOT, two vowel, one consonant, & one phrase duration). For the phrase taken from the oral reading passage, six fluent measures were obtained (i.e., one VOT, three vowel, one consonant, & one phrase duration). Results demonstrated that only one of the five measurements taken during the isolated phrase condition was significantly different between the groups. Three of the six measures obtained from the phrase taken from the oral reading condition revealed significant between-group differences. No group differences were associated with the repetitions of either phrase for any of the dependent measures for both groups. These findings suggest that the length and complexity of the speech tasks used to obtain acoustic measures of stutterers' fluency play an important role in the discovery of differences between the fluency of the two groups.