"You say tomato I say tomahto": Does social inhibition of return emerge when two people execute different actions?


Numerous studies have revealed that reaction time (RT) to a target stimulus is longer when the stimulus appears in the same spatial location as a previous stimulus relative to when the stimulus is presented at a different location. This phenomenon, termed inhibition of return (IOR), has most often been studied with participants responding to stimuli on their own (individual or iIOR). More recently IOR has also been found when a participant observes the response of another individual immediately before responding themselves (social or sIOR). The present study aimed to determine if sIOR occurs when participants perform different actions in response to shared target stimuli. Participants sat opposite each other and responded to the same stimuli, but performed different actions in response to the targets – one performed aiming movements, one performed key presses. Using spectacles with liquid crystal lenses, vision of a partner’s action was manipulated such that in the Restricted Vision condition the stimulus onset and end-point of a partner’s action were not seen. In the Full Vision condition, stimulus onset and the partner’s entire response was visible to the observer prior to their own action. As expected, sIOR was seen in all Full Vision conditions. Of greater theoretical interest, sIOR did not emerge in the Restricted Vision condition when participants observed an action different from their own immediately before responding. The present results suggest that, in sIOR paradigms, viewing different actions to one’s own fail to generate the attentional shift necessary to activate the mechanisms driving the sIOR effect.