Face inversion disrupts the perception of vertical relations between features in the right human occipito-temporal cortex

The impact of inversion on the extraction of relational and featural face information was investigated in two fMRI experiments. Unlike previous studies, the contribution of horizontal and vertical spatial relations were considered separately since they have been shown to be differentially vulnerable to face inversion (Goffaux & Rossion, 2007). Hence, inversion largely affects the perception of vertical relations (e.g. eye or mouth height) while the processing of features (e.g. eye shape and surface) and of horizontal relations (e.g. inter-ocular distance) is affected to a far lesser extent. Participants viewed pairs of faces that differed either at the level of one local feature (i.e. the eyes) or of the spatial relations of this feature with adjacent features. Changes of spatial relations were divided into two conditions, depending on the vertical or horizontal axis of the modifications. These stimulus conditions were presented in separate blocks in the first (block) experiment while they were presented in a random order in the second event-related (ER) experiment. Face-preferring voxels located in the right-lateralized middle fusiform gyrus (rMFG) largely decreased their activity with inversion. Inversion-related decreases were more moderate in left-lateralized middle fusiform gyrus (IMFG). ER experiment revealed that inversion affected rMFG and IMFG activity in distinct stimulus conditions. Whereas inversion affected IMFG processing only in featural condition, inversion selectively affected the processing of vertical relations in rMFG. Correlation analyses further indicated that the inversion effect (IE) observed in rMFG and right inferior occipital gyrus (HOG) reliably predicted the large behavioural IE observed for the processing of vertical relations. In contrast, IMFG IE correlated with the weak behavioural IE observed for the processing of horizontal relations. Our findings suggest that face configuration is mostly encoded in rMFG, whereas more local aspects of face information, such as features and horizontal spatial relations drive IMFG processing. These findings corroborate the view that the vulnerability of face perception to inversion stems mainly from the disrupted processing of vertical face relations in the right-lateralized network of face-preferring regions (rMFG, rIOG).