Influence of numerical magnitudes on the free choice of an object position.

The link between numerical magnitude and mechanisms of spatial orienting has been underlined in an increasing number of studies. Similarly, the relationship between numerical magnitude and grasping actions has started to be investigated. The present study focuses on the influence of numerical magnitude processing in the free choice of the position of an object. Participants were presented with a digit (1-9 without 5) and were required to decide whether it was smaller or larger than 5. Then, they had to grasp a small cube and change its position before vocally responding “higher” or “lower”. Results showed that in the initial phase of the grasp movement the grip aperture was modulated by the numerical magnitude. Moreover, participants shifted the position of the cube more leftward with smaller digits compared to larger ones, and they tended to position the object closer to themselves with smaller digits compared to larger ones. These results extend previous findings indicating that the processing of magnitude is tightly related to the mechanisms of spatial orienting that subserve action execution.