Task-dependent early latency (30-60 ms) visual processing of human faces and other objects.
Electrophysiological responses to previously seen faces reportedly differ from those to novel faces at shorter latencies than generally associated with complex visual analysis. It is unclear, however, whether such observations are unique to faces, and which stages of visual processing they reflect. MEG was used in 21 normal adults to record neural responses to images of faces, other objects and abstract patterns presented individually as part of a classification task and in sequential pairs as part of an image comparison task. The amplitudes of the short latency responses (30-60 ms) to the first image in pairs of faces were significantly greater than the responses to both the second faces and the individual face images. These early responses were recorded over predominantly right hemisphere parietal and occipito-temporal cortical regions including areas that, at longer latencies, have been associated with face specific activity. The differences in the responses within pairs were less for non-face objects and absent for abstract geometrical patterns. No early neuronal activity was observed in the classification task. The results indicate the existence of early latency neural networks that are sensitive to both stimulus type and task and are strongly activated by faces.