Attention in (Joint) Action

Observing actions performed by others can activate the corresponding motor representations in the primary motor cortex (M1), the so-called direct matching. However, it has been proved that in interactive social contexts this imitative tendency could turn into readiness to perform a dissimilar complementary action. To date, whether or not the observation-execution transformation is automatic (i.e. occurs without attention) is debated. In the present study we aim to bring an increase in the literature by assessing the role of spatial attention during observation of social and non social actions. The stimuli used were action sequences eliciting (or not) complementary responses (i.e. incongruent to the observed action) and spatial attention was manipulated by means of a red dot cue. First, eye-tracking procedures were used to measure the spontaneous allocation of overt spatial attention during action observation. Second, we combined transcranial magnetic stimulation (TMS) over M1 and electromyography recordings to assess the excitability of corticospinal projections to hand muscles while participants were observing the action stimuli. Results show that the allocation of spatial attention towards an observed body part is crucial for direct matching to occur. Conversely, the allocation of spatial attention plays no role when the observed action evokes an interactive complementary motor response. Overall, the present research provides one of the first evidence that social motor preparation is impervious to spatial attentional allocation.