The effect of gap duration on the perception of fluent versus disfluent speech

Gap duration contributes to the perception of utterances as fluent or disfluent, but few studies have systematically investigated the impact of gap duration on fluency judgments. The purposes of this study were to determine how gaps impact disfluency perception, and how listener background and experience impact these judgments.

Sixty participants (20 adults who stutter [AWS], 20 speech-language pathologists [SLPs], and 20 naïve listeners) listened to four tokens of the utterance, "Buy Bobby a puppy," produced at typical speech rates. The gap duration between "Buy" and "Bobby" was systematically manipulated with gaps ranging from 23.59 ms to 325.44 ms. Participants identified stimuli as fluent or disfluent.

The disfluency threshold - the point at which 50 % of trials were categorized as disfluent - occurred at a gap duration of 126.46 ms, across all participants and tokens. The SLPs exhibited higher disfluency thresholds than the AWS and the naïve listeners.

This study determined, based on the specific set of stimuli used, when the perception of utterances tends to shift from fluent to disfluent. Group differences indicated that SLPs are less inclined to identify disfluencies in speech potentially because they aim to be less critical of speech that deviates from "typical".