Number magnitude potentiates action judgements

Motor actions can be simulated and generated through the perception of objects and their characteristics. Such functional characteristics of objects with given action capabilities are called affordances. Here we report an interaction between the perception of affordances and the processing of numerical magnitude, and we show that the numerical information calibrates the judgement of action even when no actual action is required. In Experiment 1, participants had to judge whether they would be able to grasp a rod lengthways between their thumb and index finger. The presentation of the rod was preceded by a number or a non-numerical symbol. When a small number preceded the rod, participants overestimated their grasp; conversely, when a large number preceded the rods, they underestimated their grasp. In Experiment 2, participants were requested to judge if two successive rods had the same length, a judgement that did not involve any grasping. The numerical primes had no effect on this judgement, showing that the magnitude/affordance interaction was not due to a simple perceptual effect. Finally, Experiment 3 showed that the interaction was not present with a non-numerical ordered sequence, thereby eliminating sequence order as a potentially confounding variable.