Repeats, Reformulations, and Emotional Speech: Evidence for the Design of Human-Computer Speech Interfaces

Firstly, the acoustic characteristics of the users’ utterances have been found to be very different if they constitute repetitions or reformulations of previous utterances. That is, if the system claims not to have understood a contribution by the speaker, the speaker will repeat his utterance, however, usually with a different stress pattern, different phrasal intonation, with a strong emphasis on exact pronunciation or even hyper−articulation, and short pauses between the words. Some of these properties may cause severe problems for current automatic speech processing systems; for instance, Levow (1998) describes that the error rate in speech recognition rises from 16% to 44% for repetitions. That means that the characteristics of an utterance are very different if it constitutes a repetition of a previous contribution, and that these differences cannot be neglected in human−computer interaction (HCI).