  We address the problem of inferring a speaker's level of certainty based on
prosodic information in the speech signal, which has application in
speech-based dialogue systems. We show that using phrase-level prosodic
features centered around the phrases causing uncertainty, in addition to
utterance-level prosodic features, improves our model's level of certainty
classification. In addition, our models can be used to predict which phrase a
person is uncertain about. These results rely on a novel method for eliciting
utterances of varying levels of certainty that allows us to compare the utility
of contextually-based feature sets. We elicit level of certainty ratings from
both the speakers themselves and a panel of listeners, finding that there is
often a mismatch between speakers' internal states and their perceived states,
and highlighting the importance of this distinction.
