Concurrent processing reveals competition between visual representations of faces.

Scalp electrophysiological recordings in humans indicate that the processing of faces differs from other categories between 100 and 200 ms after stimulus onset, peaking at the N170. To test the effect of the addition of a second face stimulus in the visual field on the face-related N170, we measured this component in response to a laterally presented face stimulus while subjects were processing either a central face or a control stimulus. As early as 130 ms following the lateralized face stimulus, there was a strong (approximately 40% of signal) and specific reduction of the N170 amplitude when subjects were concurrently processing a central face. This observation suggests that the early stages of the N170 reflect the activation of individual faces having overlapping and competing neural representations in the human occipito-temporal cortex.