FACE RECOGNITION AS A FUNCTION OF SOCIAL ATTENTION IN NONHUMAN-PRIMATES - AN ERP STUDY

Epidural event related potentials (ERPs) were recorded from four squir rel monkeys (Saimiri sciureus) during the presentation of pictoral sti muli that comprised real human and monkey faces. Subjects viewed tachi stoscopically presented stimuli belonging to four different categories : familiar and unfamiliar human faces, and familiar and unfamiliar mon key faces. Familiar faces were subcategorized into top, middle and bot tom according to the perceived individual's dominance ranking in a soc ial hierarchy, as rated by human judges observing the group's social b ehavior. Waveform peak components to monkey and human faces showed sim ilarities in their spatial distribution. However, larger amplitude N1 and N2 components were elicited in response to monkey compared to huma n faces; particularly over lateral temporo-parietal sites. A similar t rend was observed for the P3 component, with maximal differences along midline electrode sites. Responses to familiar and unfamiliar monkey faces showed larger N1s to familiar monkey faces and larger P3s to unf amiliar monkey faces. N1 and P3 components elicited by human faces sho wed no significant differences between conditions. N2 amplitudes were larger over posterior sites for top-ranked monkeys and larger over fro ntal sites for middle-and bottom-ranked monkeys. Top-ranked human face s elicited the largest N2 components, middle-ranked faces the next lar gest, and bottom-ranked faces the smallest. N1, N2, and P3 latencies w ere similarly sensitive to the ranking of human but not monkey faces. These data suggest that non-human primates exhibit evoked potentials t o conspecific and non-conspecific faces that are similar in morphology but different in function. Larger amplitude responses to monkey faces suggests increased processing for that category of stimuli. Additiona lly, monkey ERPs reflect familiarity with conspecifics individual, aff ects the latencies and magnitudes of ERP components produced by the vi ewer. These data are consistent with social attention hypotheses which propose that higher status (i.e; more dominant or socially meaningful ) members of a group receive more attention than lower status individu als.