The effect of utterance duration on visual-speech intelligibility scores

Abstract

The effect of duration on the visual-speech intelligibility of talkers was investigated. The stimulus set consisted of 25 sentences. Each sentence had the same grammatical structure and contained three critical elements (subject, verb, object). Seven talkers were videotaped while they spoke a list of sentences twice using conversational and clear speech. For each talker, the mean duration of the conversational and clear sentences were measured. The recordings were digitized and dubbed under four conditions: (1) normal conversational; (2) conversational speech decelerated to a speed equivalent to the duration of the talker’s average utterances of clear speech; (3) natural clear speech; (4) clear speech accelerated to a speed equivalent to the talker’s average conversational speech. The test sentences (25 sentences × 2 iterations × 4 durations × 7 talkers) were randomized and shown (without sound) to a group of 18 subjects. The responses obtained during the perceptual task were used to determine each talker’s speech intelligibility for the four experimental conditions. The results revealed a significant effect for sentence duration and talker, as well as a significant sentence-duration x talker interaction. The effects of sentence duration on visual-speech intelligibility will be discussed. [Work supported by NSERC.]