Contrast of hemispheric lateralization for oro-facial movements between learned attention-getting sounds and species-typical vocalizations in chimpanzees: Extension in a second colony

Studies involving oro-facial asymmetries in nonhuman primates have largely demonstrated a right hemispheric dominance for communicative signals and conveyance of emotional information. A recent study on chimpanzee reported the first evidence of significant left-hemispheric dominance when using attention-getting sounds and rightward bias for species-typical vocalizations (Losin, Russell, Freeman, Meguerditchian, Hopkins & Fitch, 2008). The current study sought to extend the findings from Losin et al. (2008) with additional oro-facial assessment in a new colony of chimpanzees. When combining the two populations, the results indicated a consistent leftward bias for attention-getting sounds and a right lateralization for species-typical vocalizations. Collectively, the results suggest that both voluntary-controlled oro-facial and gestural communication might share the same left-hemispheric specialization and might have coevolved into a single integrated system present in a common hominid ancestor.

► We tested consistency of previous findings on oro-facial asymmetries in chimpanzees. ► Emotional vocalizations and learned vocal signals were examined with new data set. ► A consistent left cerebral specialization was found for intentional vocal signals. ► This finding raises the hypothesis of functional abilities for human speech premises. ► Also bimodal communication offers salient clues to comprehend language evolution.