Influence of manipulation of short silent pause duration on speech fluency

Ordinary speech contains disfluencies in the form of hesitations and repairs. When listeners make global judgements on speech fluency they are influenced by the frequency and nature of the individual disfluencies contained in the speech. The aim of this study was to investigate a single dimension, pause duration, in the perception of speech fluency. The method involved simulation of pause duration within naturally fluent speech by manipulating existing acoustic silences in the speech. Four conditions were created: one for the natural speech and three with step wise increases in acoustic silence durations (average x2, x4 and x7.5 respectively). In a forced choice task listeners were asked to judge the speech samples as fluent or non fluent. The results showed that the percentage of judgements of disfluency increased as the pause durations increased, and that the difference between the unmanipulated speech condition and the two conditions with the longest pause durations were statistically significant. The results were interpreted to indicate that the individual dimension of pause duration has an independent influence on the judgement of fluency in ordinary speech.