Md. Hauser et K. Andersson, LEFT-HEMISPHERE DOMINANCE FOR PROCESSING VOCALIZATIONS IN ADULT, BUT NOT INFANT, RHESUS-MONKEYS - FIELD EXPERIMENTS, Proceedings of the National Academy of Sciences of the United Statesof America, 91(9), 1994, pp. 3946-3948
In humans, the left hemisphere of the brain is dominant for processing
language. To assess the evolutionary origins of this neuropsychologic
al mechanism, playback experiments were conducted on a large populatio
n of free-ranging rhesus monkeys (Macaca mulatta). Playbacks provided
an equal opportunity to orient the right or left ear toward the speake
r. Results revealed that 61 of 80 adult rhesus favored the right ear (
left hemisphere) when vocalizations from their own repertoire were hea
rd but favored the left ear when listening to heterospecific vocalizat
ions. In contrast, infants less than a year old showed no perceptual a
symmetry for conspecific or heterospecific calls. Thus, like humans, a
dult rhesus monkeys also evidence left hemisphere dominance for proces
sing species-specific vocalizations. The emergence of such asymmetry,
however, may depend on both differential maturation of the two hemisph
eres and experience with the species-typical vocal repertoire.