VISUAL AND SOCIOCOGNITIVE INFORMATION-PROCESSING IN PRIMATE BRAIN EVOLUTION

Social group size has been shown to correlate with neocortex size in p rimates. Here we use comparative analyses to show that social group si ze is independently correlated with the size of non-V1 neocortical are as, but not with other more proximate components of the visual system or with brain systems associated with emotional cueing (e.g. the amygd ala). We argue that visual brain components serve as a social informat ion 'input device' for socio-visual stimuli such as facial expressions , bodily gestures and visual status markers, while the non-visual neoc ortex serves as a 'processing device' whereby these social cues are en coded, interpreted and associated with stored information. However, th e second appears to have greater overall importance because the size o f the V1 visual area appears to reach an asymptotic size beyond which visual acuity and pattern recognition may not improve significantly. T his is especially true of the great ape clade (including humans), that is known to use more sophisticated social cognitive strategies.