Susan Duncan, Ph.D.
University of Chicago Psychology Department,
National Yang Ming University, Taiwan, Laboratory for Cognitive Neuropsychology,
Wright State University, Department of Computer Science and Engineering.
Left- and right-brain hemisphere contributions to speech-gesture production
The gestures that people spontaneously produce when communicating interactively are heterogenous in nature. For instance, different types of gestures, or distinguishable aspects of single gestures, have different functions in conversation. Further, it is possible to distinguish systematicities of patterning in the movements of two gestural “articulators”—the dominant and non-dominant hands—in relation to the accompanying speech. The focus of this presentation will be on how co-speech gestures may inform our understanding of the different contributions of the left and right brain hemispheres to language production. Observation of the phases of physical movement of speakers’ two hands in relation to accompanying units of speech, along with assessment of the meanings manifested by the forms of gestures, permits a better understanding of the interplay between analog, imagistic thinking and levels of linguistic processing: the level of the individual utterance or “production pulse,” and that of discourse. Comparisons of gesture data from right-handed and left-handed speakers, videotaped engaging in a naturalistic, story-telling activity, reveal a tendency for the dominant hand to predominate in gestural activity. This finding is in keeping with early research by Kimura (1973). A speaker’s dominant hand is where representational gestures tend to occur; gestures that tend to synchronize with peak prosodic emphasis, utterance-by-utterance. Further careful observation of gestural activity in the non-dominant hand, however, reveals distinctive patterning in relation to shifts between larger units of discourse. Such comparative data suggest that, in line with the differing roles that have been proposed for the left and right brain in spoken language production (e.g., Beeman & Chiarello, 1998), the two hemispheres have distinguishable roles in the production of the gestures that occur with speech as well. Time permitting, the relationship of these findings to recent research concerning the impact of varying loci of brain damage on speech-gesture production will be discussed.