Abstract
Previous studies associated synchronized EEG activity in the gamma band with mechanisms involved in binding visual features during the formation of coherent percepts. Supporting this hypothesis, “scrambled” objects elicited less gamma activity than coherent familiar objects with similar physical attributes. The sensitivity of gamma activity to configuration rather than details is also evident during processing of Mooney faces, which elicited higher gamma activity when presented upright than when their face configuration is obscured by vertical inversion. In contrast, the face-sensitive ERP component (N170) is larger for inverted faces and inner face components than for upright faces suggesting that it manifests a visual mechanism sensitive to face details rather than computing their spatial configuration. Here we compared the N170 and induced gamma activity elicited by regularly configured faces (RF), faces with scrambled inner components (SF), isolated inner components preserving their normal configuration (IC), and scrambled inner components (SIC). Replicating previous findings, the N170 was smallest for RF, larger for SF and largest when only inner components were present, regardless of configuration (IC/SIC). In contrast, gamma activity around 35Hz was larger for RF and IC than for SF and SIC. These results suggest dissociation between the perceptual mechanisms manifested by N170 and those eliciting gamma activity during face perception. Specifically they support the hypothesis that N170 reflects the presence of physiognomic stimuli in the visual field, while gamma activity is enhanced by configuration and may play an important role in structural encoding of coherent face percept necessary for within category identification.
The study was funded by NIMH grant R01 MH 64458 and ISF grant 816/01.