Mauro Pesenti

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.

Finger–digit response compatibility was tested by asking participants to identify Arabic digits by pressing 1 of 10 keys with all 10 fingers. The direction of the finger–digit mapping was varied by manipulating the global direction of the hand–digit mapping as well as the direction of the finger–digit mapping within each hand (in each case, from small to large digits, or the reverse). The hypothesis of a left-to-right mental number line predicted that a complete left-to-right mapping should be easier whereas the hypothesis of a representation based on finger counting predicted that a counting-congruent mapping should be easier. The results show that when all 10 fingers are used to answer, a mapping congruent with the prototypical finger-counting strategy reported by the participants leads to better performance than does a mapping congruent with a left-to-right oriented mental number line, both in palm-down and palm-up postures of the hands, and they demonstrate that finger-counting strategies influence the way that numerical information is mentally represented and processed.