Scale-dependent spatial organisation of action observation network responses to hand actions and emotional faces

Abstract

Human social perception relies on multiple visual signals, including object-directed actions and emotional facial expressions. It remains unclear whether responses to these signals converge within action-observation regions and whether apparent convergence depends on the spatial scale of analysis. We scanned 39 healthy human adults during two block-design fMRI tasks, hand action observations contrasted with paper-tube controls, and emotional expression observations contrasted with neutral faces. Using independently defined meta-analytic action observation network (AON) ROIs in the inferior frontal gyrus (IFG), inferior parietal lobule (IPL), and posterior superior temporal sulcus (pSTS), we analysed responses at whole-brain, ROI-average, and AON-constrained voxelwise scales. Whole-brain overlap between the two contrasts was localised primarily to the left lateral occipitotemporal extrastriate cortex, outside the AON. At the regional ROI-average scale, the IFG showed positive responses to both contrasts, whereas the IPL and pSTS showed opposing task preferences. Crucially, regional IFG co-engagement did not imply that the same voxels responded to both contrasts. Suprathreshold voxelwise overlap within the AON was virtually absent, and individual-level analysis revealed a small but reliable posterior displacement of hand action relative to emotional face within IFG. These findings show that spatial convergence between hand and emotion observation responses depends on the scale of analysis. The same IFG region can be engaged by both stimulus domains while retaining distinct local response topographies.