A speaker’s level of fluency has a direct impact on a listener’s perception of that speaker who stutters. A limited number of studies have investigated listeners’ perceptions of stuttering that have been systematically altered acoustically. The purpose of the present study was to examine how three acoustically altered sound prolongation durations (200 ms, 300 ms, and 420 ms) contained within a passage affect listeners’ perceptions of stuttering; how different frequencies (5%, 10%, and 15%) of the three altered sound prolongation affect listeners’ perceptions of stuttering; how listeners’ attention process (focused versus unfocused) on altered sounds within a passage affect listeners’ perceptions of stuttering, and how a gender difference in the perception of altered sounds in a variety of duration and frequency conditions affect listeners’ perceptions of stuttering.

Eighteen adult male and 18 adult female listeners participated in the experiment. In the first condition, listeners heard word-initial voiceless fricatives within a passage that were digitally altered at 200, 300, and 420 ms at one frequency of occurrence (5, 10, or 15% stuttering). They were asked to identify the words perceived as “stuttered.” In condition two, listeners heard the passage again but were told to listen to specific words and rate the sound on a range of 1 (fluent)–100 (stuttered).

The results showed that listeners had more difficulty identifying the moments of altered sounds and rating sounds that were 200 ms in duration than 300 and 420 ms at all three frequencies. The frequency of occurrence of altered sounds also influenced listeners’ identifications and ratings for those sounds. Listeners who listened to 10 and 15% frequency conditions gave higher ratings for the speech that included altered sounds at 300 and 400 ms when they were told to focus on specific words in the passage. No significant gender differences were found for either the first or second conditions.

The findings are discussed relative to speech perception models, current knowledge of what factors contribute to listeners’ perceptual change from fluent to stuttered sounds, and the clinical implications these findings have for the field of stuttering. Directions for future research are also proposed.