How do system questions influence lexical choices in user answers?

This paper describes some studies on the effect of the system vocabulary on the lexical choices of the users. There are many theories about human-human dialogues that could be useful in the design of spoken dialogue systems. This paper will give an overview of some of these theories and report the results from two experiments that examines one of these theories, namely lexical entrainment. The first experiment was a small Wizard of Oz-test that simulated a tourist information system with a speech interface, and the second experiment simulated a system with speech recognition that controlled a questionnaire about peoples plans for their vacation. Both experiments show that the subjects mostly adapt their lexical choices to the system questions. Only in less than 5% of the cases did they use an alternative main verb in the answer. These results encourage us to investigate the possibility to add an adaptive language model in the speech recognizer in our dialogue system, where the probabilities for the words used in the system questions are increased.