What you see is what you get : motor resonance in peripheral vision

Observation of others’ actions evokes a motor resonant (MR) response, mediated by the mirror neuron system, which reflects the motor program encoding the observed actions. Presumably factors internal (attention, motivation, emotion) or external (location, salience) to observers, can modulate MR responses. We have started a series of studies evaluating the role of some of these factors, such as attention (Cerri et al. 2010) and emotion (Borroni et al. 2012). Here we explore the importance of location of the action in the visual field of observers. A grasping action was presented in the near peripheral vision of subjects (10° from fixation point), who were asked to maintain their gaze on a fixation point in the left lower corner of a computer screen while, on the right, a short video showed an avatar hand grasping a ball. Motor-evoked potentials (MEPs) were elicited in the right Opponens Pollicis by transcranial magnetic stimulation of primary motor cortex, at different delays during the observed action. Two different grasping actions were shown to two different groups of 20 subjects: a normal (palmar finger flexion) or an impossible grasping (dorsal finger flexion). After the experiment, subjects were questioned about the action they had observed. All subjects, whether they had observed the normal or the impossible action, reported seeing a normal grasping movement. Consistently, the same response was recorded in both conditions: MEPs were significantly larger at all dynamic delays compared to baseline for both normal and impossible actions. Thus motor responses were elicited by observation of an action in peripheral vision, though the corresponding motor program was grossly imprecise. We propose two complementary interpretations: 1. peripheral vision did not provide enough visual information to evoke distinct MR responses in the different conditions and delays, and 2. the action that was explicitly perceived influenced the shape of responses.