Influences of hand action on the processing of symbolic numbers: a special role of pointing?

Embodied and grounded cognition theories suggest that cognitive processes are built upon sensorimotor systems. In the context of studies on numerical cognition, interactions between number processing and the hand actions of reaching and grasping have been documented in skilled adults, thereby supporting embodied and grounded cognition accounts. The present study made use of the neurophysiological principle of neural adaptation applied to repetitive hand actions to test the hypothesis of a functional overlap between neurocognitive mechanisms of hand action and number processing. Participants performed repetitive grasping of an object, repetitive pointing, repetitive tapping, or passive viewing. Subsequently, they performed a symbolic number comparison task. Importantly, hand action and number comparison were functionally and temporally dissociated, thereby minimizing context-based effects. Results showed that executing the action of pointing slowed down the responses in number comparison. Moreover, the typical distance effect (faster responses for numbers far from the reference as compared to close ones) was not observed for small numbers after pointing, while it was enhanced by grasping. These findings confirm the functional link between hand action and number processing, and suggest new hypotheses on the role of pointing as a meaningful gesture in the development and embodiment of numerical skills.