Spoken language variation over time and state in a natural spoken dialog system

We are interested in adaptive spoken dialog systems for automated services. Peoples' spoken language usage varies over time for a fixed task, and furthermore varies depending on the state of the dialog. We characterize and quantify this variation based on a database of 20 K user-transactions with AT&T's experimental `How May I Help You?' spoken dialog system. We then report on a language adaptation algorithm which was used to train state-dependent ASR language models, experimentally evaluating their improved performance with respect to word accuracy and perplexity