EEG Investigation of Laterality in Joint Speech
In a pilot fMRI experiment done mainly by Kyle Jasmin and Sophie Scott at the Institute for Cognitive Neuroscience in University College London, we found that cortical activity seemed to be markedly different when subjects spoke in unison with a live speaker compared to speaking in synchrony with a recording. Specifically, when speaking with a live speaker, there was greatly increased activity in the right hemisphere, in areas normally associated with speech processing in the left hemisphere. These included the anterior and posterior auditory processing pathways and the right homologue of Broca’s area. Furthermore, it appeared that when speaking in unison with a live speaker, the cortical signature of the distinction between the voice of the subject and the voice of the others was altered, or absent. This represents a suggestive alignment between the neuroscience and the experience, often repeated, of losing oneself when chanting. The results were published in J. Neuroscience:
Jasmin, K. M., McGettigan, C., Agnew, Z. K., Lavan, N., Josephs, O., Cummins, F., & Scott, S. K. (2016). Cohesion and Joint Speech: Right Hemisphere Contributions to Synchronized Vocal Production. The Journal of Neuroscience, 36(17), 4669-4680.
It should be possible to use EEG to examine lateralization when speaking in a variety of conditions, including speaking in synchrony with a live speaker and speaking in synchrony with a recording. My hunch is that spectral power in the 30 to 50 Hz region is the right place to look. This would require a somewhat non-standard set-up, in which potential difference is measured between an electrode on the side and one on the mid-line, with the same central referent being used for both lateral electrodes.
If you have an EEG set-up and are interested in discussing this and running a quick pilot study, do get in touch.