Rigid Head Motion in Expressive Speech Animation: Analysis and Synthesis
Rigid head motion is a gesture that conveys important nonverbal information in human communication, and hence it needs to be appropriately modeled and included in realistic facial animations to effectively mimic human behaviors. In this paper, head motion sequences in expressive facial animations are analyzed in terms of their naturalness and emotional salience in perception. Statistical measures are derived from an audiovisual database, comprising synchronized facial gestures and speech, which revealed characteristic patterns in emotional head motion sequences. Head motion patterns with neutral speech significantly differ from head motion patterns with emotional speech in motion activation, range, and velocity. The results show that head motion provides discriminating information about emotional categories. An approach to synthesize emotional head motion sequences driven by prosodic features is presented, expanding upon our previous framework on head motion synthesis. This method naturally models the specific temporal dynamics of emotional head motion sequences by building hidden Markov models for each emotional category (sadness, happiness, anger, and neutral state). Human raters were asked to assess the naturalness and the emotional content of the facial animations. On average, the synthesized head motion sequences were perceived even more natural than the original head motion sequences. The results also show that head motion modifies the emotional perception of the facial animation especially in the valence and activation domain. These results suggest that appropriate head motion not only significantly improves the naturalness of the animation but can also be used to enhance the emotional content of the animation to effectively engage the users