A specific positive component of the event-related potential, thought to be elicited by faces, and observed in infants but not adults. It has been suggested to be a precursor to the negative component N170 compared to which it differs not only in polarity, but also peaks at a later latency. These peak latencies decrease from 450 to 390 ms between 3 and 12 months-of-age, being most evident over posterior and lateral electrodes. However, P400 shares a couple of similarities with the adult N170 even though it is opposite in polarity and has a later latency that the adult N170: both are prominent at the lateral than medial electrodes, and for both the peak latency is faster for faces than for objects. In a study exploring the featural and configural information involved in face processing, it was found that the P400 in 8 month- relative to 4 month-old infants almost mirrored the pattern of outcomes for N170 in adults: greater featural changes in the left compared to the right hemisphere, equal amplitude in the configural changes across both hemispheres, and a greater amplitude in response to the configural rather than featural changes in the right hemisphere. These findings, among others, led to the conclusion that indeed P400 constitutes a developmental precursor to N170.
See Event-related (brain) potentials (ERPs), Face processing, N170