Different grasping experiences affect mapping effects but not correspondence effects between stimulus size and response location.

The so-called spatial-size association of response codes (SSARC) effect denotes that humans respond faster and more accurately with a left response to physically small stimuli and a right response to physically large stimuli, as compared to the opposite mapping. According to an application of the CORE principle to the SSARC effect, the habit to grasp larger/heavier objects with one's dominant hand and smaller/lighter objects with one's non-dominant hand creates spatial-size associations. We investigated if grasping habits play a causal role in the formation of spatial-size associations by testing if the mapping of a preceding object-grasping task affects the size of the SSARC effect in subsequent choice-response tasks with keypress responses. In the object-grasping task, participants were instructed to grasp wooden cubes of variable size either according to a compatible (small-left; large-right) or according to an incompatible (small-right; large-left) mapping. In the choice-response tasks, participants responded with left or right keypresses to the size or color of a small or large stimulus. The results showed that participants with the compatible mapping in the object-grasping task showed a larger SSARC effect in the size discrimination task, but not in the color discrimination task, than participants with the incompatible mapping in the object-grasping task. Results suggest that a short period of practice with different size-location mappings can modulate size-location links used for controlled S-R translation, but not links underlying automatic S-R translation. In general, the results support the hypothesis that grasping habits play a causal role in the formation of spatial-size associations.