Making sense of objects lying around: How contextual objects shape brain activity during action observation

Action recognition involves not only the readout of body movements and involved objects but also the integration of contextual information, e.g. the environment in which an action takes place. Notably, inferring superordinate goals and generating predictions about forthcoming action steps should benefit from screening the actor's immediate environment, in particular objects located in the actor's peripersonal space and thus potentially used in following action steps. Critically, if such contextual objects (COs) afford actions that are semantically related to the observed action, they may trigger or facilitate the inference of goals and the prediction of following actions. This fMRI study investigated the neural mechanisms underlying the integration of COs in semantic and spatial relation to observed actions. Specifically, we tested the hypothesis that the inferior frontal gyrus (IFG) subserves this integration. Participants observed action videos in which COs and observed actions had common overarching goals or not (goal affinity) and varied in their location relative to the actor. High goal affinity increased bilateral activity in action observation network nodes, i.e. the occipitotemporal cortex and the intraparietal sulcus, but also in the precuneus and middle frontal gyri. This finding suggests that the semantic relation between COs and actions is considered during action observation and triggers (rather than facilitates) processes beyond those usually involved in action observation. Moreover, COs with high goal affinity located close to the actor's dominant hand additionally engaged bilateral IFG, corroborating the view that IFG is critically involved in the integration of action steps under a common overarching goal.