Disentangling dynamic information and temporal order processing of human action perception

Human action perception involves processing dynamic information in its temporal order. However, previous studies investigating action perception have not yet distinguished between the presence of dynamic information and the temporal order in which dynamic information unfolds within the context of a single action. Using 3-T functional MRI, we presented participants with brief, single-actor, whole-body actions viewed either as still images, as intact videos, or as videos consisting of short dynamic fragments with the order temporally scrambled. Regions classically associated with action perception showed higher activity for dynamic compared with still stimuli, regardless of the temporal continuity in the dynamic stimuli. However, two clusters in the right inferior parietal lobule (IPL) differentiated between the intact and temporally scrambled videos. Specifically, the right angular gyrus (AG) showed a preference for the intact videos over the temporally scrambled ones, while the right supramarginal gyrus (SMG) showed the opposite pattern. Combined with previous literature, we argue for the role of the IPL as a temporospatial buffer, with the SMG processing dynamic information on short timescales and the AG processing on longer timescales. Our results underscore the need to consider dynamic information and temporal order separately in investigations of action perception.