To create conversational systems with human-like listener behavior, generating short feedback responses (e.g., “mhm”, “ah”, “wow”) appropriate for their context is crucial. These responses convey their communicative function through their lexical form and their prosodic realization. In this paper, we transplant the prosody of feedback responses from human-human U.S. English telephone conversations to a target speaker using two synthesis techniques (TTS and signal processing). Our evaluation focuses on perceived naturalness, contextual appropriateness and preservation of communicative function. Results indicate TTS-generated feedback were perceived as more natural than signal-processing-based feedback, with no significant difference in appropriateness. However, the TTS did not consistently convey the communicative function of the original feedback.

There has been a lot of work on predicting the timing of feedback in conversational systems. However, there has been less focus on predicting the prosody and lexical form of feedback given their communicative function. Therefore, in this paper we present our preliminary annotations of the communicative functions of 1627 short feedback tokens from the Switchboard corpus and an analysis of their lexical realizations and prosodic characteristics. Since there is no standard scheme for annotating the communicative function of feedback we propose our own annotation scheme. Although our work is ongoing, our preliminary analysis revealed lexical tokens such as “yeah” are ambiguous and therefore lexical forms alone are not indicative of the function. Both the lexical form and prosodic characteristics need to be taken into account in order to predict the communicative function. We also found that feedback functions have distinguishable prosodic characteristics in terms of duration, mean pitch, pitch slope, and pitch range.