Synthesized speech intelligibility and persuasion : speech rate and non-native listeners

This experiment assessed the effect of variation in speech rate on comprehension and persuasiveness of a message presented in text-to-speech (TTS) synthesis to native and non-native listeners. Eighty non-native speakers of English and 80 native speakers of Australian English were randomly assigned to listen to eight banking product descriptions under one of four conditions: normal rate (155 words per minute) with no background noise, normal rate with multi-talker background noise (+6 dB SNR), fast-normal (178 words per minute) with no background noise, and fast-normal with multi-talker background noise. Participants completed comprehension tests and rated each product's usefulness. A faster rate lowers comprehension for both native and non-native listeners but does not influence the persuasiveness of the message. The findings have implications for the selection of speech rates for persuasive messages delivered to native and non-native listeners using TTS.