Abstract
Our goal was to use fMRI to uncover dynamics of visual scene face detection in the human brain, by means of a paradigm that slowly and gradually reveals faces. Such paradigms have been used previously to examine top-down facilitation (e.g., Eger et al., 2007; James et al., 2006) and to dissociate multiple stages in visual recognition (e.g., Carlson et al., 2006). Here, we used the RISE methods (Sadr & Sinha 2004) to create image sequences of visual scenes in which faces or cars are revealed progressively as they emerge from noise. Participants were asked to respond as soon as they detected a face or car during the sequence presentation. Among the face-sensitive regions identified based on localizer data, the right fusiform face area (“FFA”) showed the earliest difference between face and car activation. Specifically, the right FFA showed higher activation to faces than to cars before the more posteriorly located face-sensitive area of the lateral occipital cortex (“Occipital Face Area”, “OFA”). Whole-brain analysis confirmed these findings, with a face-sensitive cluster in the right fusiform gyrus showing face selectivity shortly before successful behavioral detection. Overall, these observations suggest that following low-level visual analysis, a face stimulus is detected initially by responses of populations of neurons in the right middle fusiform gyrus, spreading to a whole network of (sub)cortical face-sensitive areas for further processing. Our results provide interesting evidence for non-hierarchical emergence of face-selectivity among known face-sensitive cortical regions, that is, with “ OFA” face-specific responses not necessarily preceding face-specific “FFA” activation (Rossion, 2008).
Belgian National Fund for Scientific Research Research Grant ARC07/12-007, The Human Frontier Science Program Postdoctoral Fellowship LT00103/2008-L.