Adult humans evidence a left brain hemisphere bias for processing the formal properties of language (e.g., semantics) and a right hemisphere bias for processing the emotional content of language (e.g., intonation, affect). There is also evidence of hemispheric biases in processing facial expressions, contingent upon whether the emotion is positive or negative. The evolutionary origins of these asymmetries remain unclear. This proposal has been designed to address this gap in our understanding, conducting research on a population of semi-free-ranging rhesus macaques. Part one explores asymmetry in facial expression and tests the hypothesis that negative/withdrawal emotions are associated with a right brain hemisphere/left side of the face bias, whereas positive/approach emotions are associated with left hemisphere/right side of the face biases. Possible developmental changes in this pattern of expression will be assessed by recording from infants and adults. Part two studies perception of vocalizations, using playback experiments to assess whether rhesus monkeys evidence a left hemisphere bias/right ear bias. Natural and manipulated calls will be used. Part three examines whether rhesus monkeys show a left hemisphere/right side of the face bias during vocal production, as occurs in human adults while speaking.
