Event-related potentials related to normal and morphed emotional faces

S. Bentin and L. Y. Deouell (2000) have suggested that face recognition is achieved through a special-purpose neural mechanism, and its existence can be identified by a specific event-related potential (ERP) correlate, the N170 effect. In the present study, the authors explored the structural significance of N170 by comparing normal vs. morphed stimuli. They used a morphing procedure that allows a fine modification of some perceptual details (first-order relations). The authors also aimed to verify the independence of face identification from other cognitive mechanisms, such as comprehension of emotional facial expressions, by applying an emotion-by-emotion analysis to examine the emotional effect on N170 ERP variation. They analyzed the peak amplitude and latency variables in the temporal window of 120-180 ms. The ERP correlate showed a classic N170 ERP effect, more negative and more posteriorly distributed for morphed faces compared with normal faces. In addition, they found a lateralization effect, with a greater right-side distribution of the N170, but not directly correlated to the morphed or normal conditions. Two cognitive codes, structural and expression, are discussed, and the results are compared with the multilevel model proposed by V. Bruce and A. W. Young (1986, 1998).