Neural Correlates of Holistic Face Processing

Holistic processing is the tendency to perceive an object as an indecomposable whole rather than by its parts. Psychological research has shown that faces are processed holistically. However, recent studies have shown that non-expertise objects with salient Gestalt information are also processed holistically, questioning whether this phenomena is unique to faces. Neuroimaging studies have linked holistic processing of faces to brain activity in face-responsive regions of the occipital-temporal cortex. However, these studies specifically localized face-responsive brain regions, but not object, scene or perceptual grouping related brain regions. In this study, we aimed to explore the neural correlates of holistic face processing in a larger range of brain regions, in order to investigate how specific the activation is to face regions. We used fMRI to record the brain activity of subjects performing a composite face task. Participants viewed pairs of faces and determined whether the top halves of the faces were the same or different. Additionally, we localized specific regions of interest defined by their responses to faces, objects, scenes and perceptual grouping, allowing us to investigate how activity in these regions changed during the composite face task. Surprisingly, we found that activity in the occipital face area, fusiform face area and anterior temporal face area did not show a clear pattern of activity relating to the behavioural composite effect. However, activity in the parahippocampal place area, superior parietal lobule and early visual cortex all showed a pattern of activity consistent with the behavioural composite effect. These results suggest that holistic processing occurs in brain regions involved in spatial processing, perceptual grouping and early vision, rather than being limited to face-responsive brain regions. We hypothesize that holistic perception may be driven by these factors rather than identity discrimination, in line with the behavioural finding of the composite effect in non-expertise objects