Abstract
Recent studies have revealed that stimuli of high valence can activate the emotional system in the human brain without observers' awareness. In the current study, we used event-related fMRI to measure the hemodynamic response of face-selective brain regions when observers viewed neutral, fearful and scrambled faces. These stimuli were either presented consciously or rendered invisible through interocular suppression. Using scrambled faces as the baseline, results show that both the fusiform face area (FFA) and superior temporal sulcus (STS) had strong activations to visible neutral and fearful faces. In the suppressed condition, when observers were not aware of the face pictures, the FFA still showed substantial activation for both invisible neutral and fearful faces, whereas the STS only responded to invisible fearful faces. This pattern of results suggests that FFA and STS play different roles in the processing of facial information. Our observation provides further support for the dissociable neural systems that are specialized for facial structural encoding vs. facial expression analysis (Bruce & Young, 1986, BJP) or invariant aspects of faces vs. changeable aspects of faces (Haxby et al., 2000, TICS). More surprisingly, the separate functions for facial information processing were only revealed in the invisible condition. We hypothesize that when images were suppressed interocularly, the observed BOLD responses reflect more of a feed-forward visual information processing without the influence of the feedback modulation from conscious representation of faces, and such isolation of the feed-forward process made it possible for us to reveal the distinct functions of FFA and STS.
This research was supported by the James S. McDonnell foundation and NIH.