Effector-specific motor simulation supplements core action recognition processes in adverse conditions.

Observing other people acting activates imitative motor plans in the observer. Whether, and if so when and how, such "effector-specific motor simulation" contributes to action recognition remains unclear. We report that individuals born without upper limbs (IDs) - who cannot covertly imitate upper limb movements - are significantly less accurate at recognizing degraded (but not intact) upper-limb than lower-limb actions (i.e., point-light animations). This finding emphasizes the need to reframe the current controversy regarding the role of effector-specific motor simulation in action recognition: instead of focusing on the dichotomy between motor and non-motor theories, the field would benefit from new hypotheses specifying when and how effector-specific motor simulation may supplement core action recognition processes to accommodate the full variety of action stimuli that humans can recognize.