Action observers implicitly expect actors to act goal-coherently, even if they do not: an fMRI study

Abstract

Actions observed in everyday life normally consist of one person performing sequences of goal-directed actions. The present fMRI study tested the hypotheses that observers are influenced by the actor's identity, even when this information is task-irrelevant, and that this information shapes their expectation on subsequent actions of the same actor. Participants watched short video clips of action steps that either pertained to a common action with an overarching goal or not, and were performed by either one or by varying actors (2 × 2 design). Independent of goal coherence, actor coherence elicited activation in dorsolateral and ventromedial frontal cortex, together pointing to a spontaneous attempt to integrate all actions performed by one actor. Interestingly, watching an actor performing unrelated actions elicited additional activation in left inferior frontal gyrus, suggesting a search in semantic memory in an attempt to construct an overarching goal that can reconcile the disparate action steps with a coherent intention. Post-experimental surveys indicate that these processes occur mostly unconsciously. Findings strongly suggest a spontaneous expectation bias toward actor-related episodes in action observers, and hence to the immense impact of actor information on action observation.

Keywords: action recognition; episodic knowledge; functional MRI; person perception; ventrolateral prefrontal cortex.

Figure 1

Stimuli and trial structure. Video clips showed action steps that either pertained to an overarching goal or not. Actions were performed either by one or by varying actors resulting in four conditions BC (here depicted in green), GC (red), AC (yellow), NC (blue). Video trials were occasionally followed by question trials (here depicted in orange) that required participants to confirm or reject a verbal action description (e.g., salting a tomato) with respect to the preceding trial. Trial succession was arranged such that five to seven films of one condition added up to one episode. Episodes were partially overlapping with episodes of other conditions, that is, video clips of one episode were mostly not shown in direct succession. A representative video sequence is provided in Supporting Information.

Figure 2

Parametric effect of unfolding of episodes with incoherent goals but coherent actors (AC), that is, increase in activation from the first to the last clip of an episode (z > 2.576; corrected cluster threshold P < 0.05); IFG inferior frontal gyrus, vmPFC ventromedial prefrontal cortex, SFS/MFG superior frontal sulcus/middle frontal gyrus.

Figure 3

Conjunction of the parametric effects of unfolding of actor‐coherent episodes, independent of goalcoherence [BC ∩ AC] (z > 2.576; corrected cluster threshold P < 0.05); aSFS anterior superior frontal sulcus, vmPFC ventromedial prefrontal cortex.

Figure 4

Main effect of actor coherence in ROI analyses for left anterior superior frontal sulcus (aSFS) and ventromedial prefrontal sulcus (vmPFC). Coordinates of ROI were derived from a trial split procedure to prevent double dipping [Kriegeskorte et al., 2009]. The effect of actor coherence is demonstrated by mean beta values extracted from conditions actor‐coherent goal‐coherent (BC), actor‐incoherent goalcoherent (GC), actor‐coherent goal‐incoherent (AC), and actor‐incoherent goal‐incoherent (NC) (error bars indicate standard errors).

Figure 5

Conjunction of the main effects of actor coherence versus incoherence, independent of goal coherence [([BC>GC) ∩ (AC>NC)] (z > 2.576; corrected cluster threshold P < 0.05); FFA Fusiform face area, vmPFC ventromedial prefrontal cortex.