The relationship between right hemisphere damage and gesture in spontaneous discourse
Cocks, N., Hird, K., & Kirsner, K. (2007). The relationship between right hemisphere damage and gesture in spontaneous discourse. Aphasiology, 21(3/4), 299-319. doi:10.1080/02687030600911393
Background: The assessment and rehabilitation of acquired neurogenic communication disorders rarely involves a systematic analysis of gesture use. The right cerebral hemisphere has been identified as a possible locus of control for gesture. McNeill's (McNeill & Duncan, 2000) growth point theory posits a structure for the organisation of processes from both cerebral hemispheres which serves to support the integration of gestural and verbal messages that emerge from a non-modality specific cognitive growth point or idea unit.
Aims: The first aim of this research was to describe male non-brain-damaged (NBD) speakers' gesture use in the context of spontaneous discourse. The second aim was to compare the gesture production patterns of five individual males with right cerebral hemisphere damage (RHD) with the NBD group's pattern of performance.
Methods and Procedures: Gesture rates and variation of fundamental frequency were analysed across four speaking conditions; a personal narrative, two procedural narratives, two emotional narratives, and three comic book descriptions. The discourse stimuli were selected to elicit highly emotional versus neutral content. Gesture use was classified according to the system described by McNeill (1992) for digital video analysis. Discourse samples were segmented into intonational phrases (Pierrehumbert & Hirschberg, 1990). Gesture rates and variation in fundamental frequency were calculated within intonational phrases.
Outcomes and Results: The NBD group demonstrated higher rates of body beats and head movements in discourse samples with high emotional content. Procedural narratives were accompanied by higher rates of representational gestures than in the other conditions. The RHD participants showed variability in their gesture use across the discourse genres. The majority of RHD participants used lower non-body-focused gesture rates but significantly fewer gestures in the discourse samples with high emotional content. Differences in visuo-spatial ability, variations in fundamental frequency of speech, and body-focused gesture failed to reveal systematic patterns in the RHD participants.
Conclusions: McNeill's (1992) growth point theory provides a useful platform for interpreting the observed reduction in overall frequency of gesture use evident in the RHD participants, but cannot account for the observed interaction involving the emotional narrative. While the impact of emotion on gesture in the non-brain-damaged population was unsurprising, the reversal of this pattern in people with right hemisphere damage poses a challenge for theoretical work in this area. The results of this study indicate that the analysis of gesture use is important for a deeper understanding of expressive communication impairments associated with acquired neurogenic impairment.