Abstract
How is perceiving the gender of a face distinct from perceiving its identity? Here we report results from visual search and divided attention experiments that show differences in how faces are visually processed in each case. In our visual search experiments, we tested for visual field advantages in search performance. Observers searched for target faces in arrays of faces divided between the left (LVF) and right (RVF) visual fields. Faces were morphed such that target faces always differed from distractor faces by 30%. Crucially, this 30% morph difference corresponded to a change in either (a) morph but not identity, (b) identity only, or (c) identity and gender. Our results showed an RVF advantage for gender-based searches and an LVF advantage for identity-based searches. We interpret our findings as evidence of categorical perception of face gender but not identity. Our visual search results suggested serial processing in both cases, which we followed up using a divided field dual-task paradigm to test for potential differences in visual processing capacity limitations for face pairs (instead of six-face arrays). Our method allowed us to measure the cost of dividing visual processing resources between the two faces. Observers performed either a gender- or identity-based task, for one (single-task) or both of the faces (dual-task). In contrast to our visual search results, which showed no evidence of parallel face processing, we found that observers were able to judge the gender, but not the identity, of two faces in parallel. Taken together, our results show clear differences in the way faces are visually processed depending on the relevance of gender or identity to the task. Specifically, perception of face gender is left-lateralized and can occur in parallel whereas perception of face identity is right-lateralized and occurs serially.