Motor resonance in peripheral vision and the role of covert attention

In this study we investigate whether action observation in peripheral vision evokes a motor resonant (MR) response and whether this response can be modulated by the attention of observers. Two groups of subjects observed two different actions -either a ‘natural’ or an ‘impossible’ hand grasping performed by an avatar- that were shown on the right side of a computer screen, at 10° from their fixation point. TMS-evoked motor potentials (MEPs) were recorded in the Opponens Pollicis (OP) and in the Abductor Digiti Minimi (ADM) muscles at different delays during the observation of the 4s video showing one of the grasping actions. In Experiment 1 subjects were asked to maintain their gaze on a fixation point, while viewing the action in peripheral vision; in Experiment 2 different subjects were asked to do the same but also to pay covert attention at the video showed in periphery. Eye movements were monitored. Results show that MEPs in both muscles were significantly modulated by observation of both possible and impossible actions shown in peripheral vision, although the overall MR responses were grossly imprecise in timing and muscle specificity and did not differentiate between the two actions. However, when subjects paid covert attention to the grasping action the specificity of the MR response improved, showing a different modulation in the two muscles consistent with (but not equal to) their activation during observation of the two actions in foveal vision. These results support the hypothesis that MR responses are shaped by both sensory and cognitive processes.