Abstract
Upside-down inversion is thought to disrupt the processing of spatial relations between the features of a face, i.e. its configuration, while largely preserving the processing of local features. However, recent studies challenged this view, suggesting that inversion equally impairs the perception of features and their relations (e.g. Yovel & Kanwisher, 2004). To resolve these discrepancies and clarify the impact of inversion on the perception of a face stimulus, we dissociated between the vertical and horizontal relations between face features. In three experiments, subjects discriminated pairs of faces that differed at the level of vertical relations (eyes upper or lower in the face), horizontal relations (eyes closer or further apart) and feature shape (eyes exchanged). Face pairs were presented upright and inverted. A dramatic performance decline for inverted faces was obtained in the vertical-relational condition, whereas an equally moderate impairment was observed in the featural and horizontal-relational conditions. This pattern was observed whether the differences to detect between faces in vertical-relational and horizontal-relational were equalized by considering the relative distance between the two eyes (experiment 1), or when they were considered as separate entities (experiments 2 and 3). Whether upright and inverted pairs were blocked or randomly interleaved in the experiment had no influence on this pattern of results (experiment 3). These experiments provide clear evidence that inversion dramatically disrupts the ability to extract vertical relations between facial features but not horizontal relations, and support the view that upright and inverted faces are processed by qualitatively different mechanisms.