This study investigates the electrophysiological mechanisms underlying face perception in humans using event-related potentials (ERPs). ERPs were recorded from scalp electrodes while subjects performed a visual target detection task, focusing on the detection of human faces among other stimuli. The results showed that faces evoked a negative potential at 172 msec (N170), which was absent for other stimuli. N170 was largest over the posterior temporal scalp and was more pronounced on the right hemisphere. The amplitude of N170 was delayed when faces were inverted but not changed in amplitude. Isolated eyes elicited a larger N170 than whole faces, while noses and lips elicited smaller negative ERPs about 50 msec later. Distorted human faces, with altered inner facial components, evoked an N170 similar to that of normal faces, suggesting that N170 may reflect a neural mechanism tuned to detect human faces rather than identify them. The N170's sensitivity to eyes in isolation suggests that it may reflect the activation of an eye-sensitive region of cortex. The voltage distribution of N170 over the scalp supports the idea that its neural generator is located in the occipitotemporal sulcus lateral to the fusiform/inferior temporal region. These findings suggest that N170 may be part of a "structural encoder" stage of face processing, similar to the N200 recorded from the middle fusiform and posterior inferior temporal gyri.This study investigates the electrophysiological mechanisms underlying face perception in humans using event-related potentials (ERPs). ERPs were recorded from scalp electrodes while subjects performed a visual target detection task, focusing on the detection of human faces among other stimuli. The results showed that faces evoked a negative potential at 172 msec (N170), which was absent for other stimuli. N170 was largest over the posterior temporal scalp and was more pronounced on the right hemisphere. The amplitude of N170 was delayed when faces were inverted but not changed in amplitude. Isolated eyes elicited a larger N170 than whole faces, while noses and lips elicited smaller negative ERPs about 50 msec later. Distorted human faces, with altered inner facial components, evoked an N170 similar to that of normal faces, suggesting that N170 may reflect a neural mechanism tuned to detect human faces rather than identify them. The N170's sensitivity to eyes in isolation suggests that it may reflect the activation of an eye-sensitive region of cortex. The voltage distribution of N170 over the scalp supports the idea that its neural generator is located in the occipitotemporal sulcus lateral to the fusiform/inferior temporal region. These findings suggest that N170 may be part of a "structural encoder" stage of face processing, similar to the N200 recorded from the middle fusiform and posterior inferior temporal gyri.