The timing of head movements: The role of prosodic heads and edges.

This study examines the influence of the position of prosodic heads (accented syllables) and prosodic edges (prosodic word and intonational phrase boundaries) on the timing of head movements. Gesture movements and prosodic events tend to be temporally aligned in the discourse, the most prominent part of gestures typically being aligned with prosodically prominent syllables in speech. However, little is known about the impact of the position of intonational phrase boundaries on gesture-speech alignment patterns. Twenty-four Catalan speakers produced spontaneous (experiment 1) and semi-spontaneous head gestures with a confirmatory function (experiment 2), along with phrase-final focused words in different prosodic conditions (stress-initial, stress-medial, and stress-final). Results showed (a) that the scope of head movements is the associated focused prosodic word, (b) that the left edge of the focused prosodic word determines where the interval of gesture prominence starts, and (c) that the speech-anchoring site for the gesture peak (or apex) depends both on the location of the accented syllable and the distance to the upcoming intonational phrase boundary. These results demonstrate that prosodic heads and edges have an impact on the timing of head movements, and therefore that prosodic structure plays a central role in the timing of co-speech gestures.