Face-related activity in superior colliculus and temporal cortex of primates

Face processing has been extensively studied in higher-order visual cortex (e.g., temporal cortex ‘face patches’). Recently, we reported that neurons in the macaque superior colliculus (SC) display a preference for face stimuli at extremely short latencies. Here, we directly compared face-related visual responses in the SC and temporal visual cortex. Using the same subject, stimuli, and paradigm, we recorded neurons in the middle face patch of the temporal cortex, as well as the SC, under both foveal and peripheral (6 degree contralateral) presentation conditions. In temporal cortex, with foveal presentation, 53% of visually responsive neurons exhibited a significant face preference at 100ms after stimulus onset, but only 8% displayed a face preference at 50ms. With peripheral presentation, only a minority of the same neurons exhibited a significant face preference either early (12% at 50ms) or late (14% at 100ms). In contrast, a majority of SC neurons displayed a significant face preference both early and late, for both foveal and peripheral stimulus presentations (foveal: 69% at 50ms, 43% at 100ms; peripheral: 49% at 50ms, 45% at 100ms). Overall, for temporal cortex neurons, the median latency for the face preference was 79ms and 93ms, for foveal and peripheral conditions respectively. For SC neurons, the median latencies were markedly shorter – 40ms and 42ms. Thus, a face preference emerges earlier for neurons in the SC than in the temporal cortex, and the preference is equally strong for foveal and peripheral locations for SC neurons, whereas the preference in the temporal cortex shows a strong bias towards central vision. Our results reveal distinct properties of face processing in the SC and temporal cortex that may support complementary functions in the primate visual system – rapid face detection in the visual periphery by the SC and more sophisticated face processing by temporal cortex following foveation.