Adults are expert at recognizing faces. This ability requires the encoding of subtle differences among faces in the shape of individual features (featural processing) and in the spacing among features (a kind of configural processing called second-order relational processing). Past research suggests that two separate systems underlie these types of processing:(1) The processing of features is affected less by inversion than the processing of their spacing; (2) Featural processing develops more quickly in middle childhood; (3) Early visual deprivation that reduces visual input to both hemispheres or to mainly the right hemisphere spares featural processing but causes permanent deficits in the processing of spacing (Le Grand et al., 2001, 2003; Mondloch et al., 2002). In the current study, we used fMRI to investigate the neural mechanisms in visually normal adults that differentiate the processing of facial features from the processing of their spacing. We acquired images with a 1.5 Tesla magnet while subjects (n=10) made same/different judgments about pairs of faces that were presented sequentially. Each of five runs consisted of 11 45-sec blocks: four in which faces differed only in the shape of the eyes and mouth (to tap featural processing), four in which faces differed only in the spacing of those features (to tap sensitivity to second-order relations) and three in which the images were scrambled (control set). We found a group of areas in the right frontal cortex that is less active during the processing of features than of their spacing; six frontal areas showed this pattern in 8 to 10 subjects. The Fusiform Face Area was active in both conditions but different subsections were especially active during the blocks requiring each type of face processing. This study demonstrates separate neural mechanisms underlying the processing of faces based on the shape of individual features versus their spacing.

NSERC to DM, CIHR to CG, NSERC to KO