Abstract:

The enculturated gorilla Koko (Gorilla gorilla) wields an impressive repertoire of learned vocal and breathing-related behaviors (Perlman and Clark, 2015). Video records reveal hundreds of instances in which Koko voluntarily performs coughs (glottal stops), grunts (voiced glottal fricatives), huffs (voiceless glottal fricatives), blows (bilabial fricatives), nose blows (with manually assisted nasal frication), and “raspberries” (lingual fricatives). Koko performs the vast majority of these behaviors (~ 96%) in coordination with manual gestures (e.g. blowing or coughing into her hand) or object-directed actions (e.g. huffing on the lenses of eyeglasses, grunting into a telephone). While Koko is predominantly left handed when feeding (35% of actions performed with her right hand, n=62) or scribbling with a pen on paper (3% with right hand, n=34), she prefers her right hand when performing gestures and actions associated with vocal and breathing-related behaviors (77%, n=90 bouts). She also prefers her right hand when blowing into wind instruments like recorders (59%, n = 22 bouts). Her right-hand preference in these latter behaviors suggests that her voluntary control over vocalization and breathing is lateralized in the left cerebral hemisphere. In addition, we conducted cross-correlational analyses on a subset of the corpus and found distinct patterns of synchrony between Koko’s exhalation and her manual and overall bodily movement across different behavior types. For example, when Koko blows into her hand, she tends to lead with a head movement towards her stationary hand. In contrast, when she coughs into her hand – a behavior that involves the constriction and release of her glottis – she tends to jerk her hand to her mouth with a manual movement that shortly lags the release of the cough. These analyses show a tight link between Koko’s learned vocal and breathing related behavior and her performance of manual and other bodily movements. We speculate that the coordinated control over vocalization and gesture in human speech may have roots in our common ancestor with great apes.