Sensorimotor anticipation of others' actions in real-world and video settings: modulation by level of engagement?

Electroencephalography (EEG) studies investigating social cognition have used both video and real-world stimuli, often without a strong reasoning why one or the other was chosen. Video stimuli can be selected for practical reasons, while naturalistic real-world stimuli are ecologically valid. The current study investigated modulatory effects on EEG mu (8 - 13 Hz) suppression, directly prior to the onset - and during the course - of observed actions, related to real-world and video settings. Recordings were made over sensorimotor cortex and stimuli in both settings consisted of identical (un)predictable object-related grasping and placing actions. In both settings a very similar mu suppression was found during unfolding of the action, irrespective of predictability. However, mu suppression related to the anticipation of upcoming predictable actions was found exclusively in the real-world setting. Thus, even though the presentation setting does not seem to modulate mu suppression during action observation, it does affect the anticipation-related mu suppression. We discuss the possibility that this may be due to increased social engagement in real-world settings, which in particular affects anticipation. The findings emphasise the importance of using real-world stimuli to bring out the subtle, anticipatory, aspects related to action observation.