Embodied Magnitude Processing: On the Relation Between the SNARC Effect and Perceived Reachability

Magnitude information, for instance, regarding weight, distance, or velocity, is crucial for planning goal-directed interactions. Accordingly, magnitude information, including numerical magnitude, can affect actions: responses to small numbers are faster with the left hand than the right and vice versa (hand-based SNARC effect). Previous experiments found an influence of effector placements on the SNARC effect but also an influence of the mere distance between effectors and numbers. This indicates a sensorimotor grounding of space-number processing. In the current study, we investigated this grounding by probing the SNARC effect close to and far from the hands. We used a magnitude comparison task with a fixed standard of 5 (smaller numbers 1,2,3,4; larger numbers 6,7,8,9) with a sagittal response arrangement to measure hand-based and sagittal SNARC effects for digits presented at different sagittal distances to the hands, i.e., in peripersonal and extrapersonal space. A significant sagittal SNARC effect was found, with the largest effect size in extrapersonal space. Meanwhile, the hand-based SNARC effect appeared only descriptively, with the largest effect size between the hands, i.e., in peripersonal space. Additionally, a purely spatial congruency effect surfaced, prioritizing responses with the hand closer to the number. Together, these results emphasize that responses in simple decision-making tasks can be influenced interactively by a multitude of task-relevant axes and relative spatial locations, including effector placement and stimulus placement, as well as number magnitude. Funding from the German Research Foundation (DFG) in the framework of the research unit "Modal and amodal cognition: Functions and interactions (FOR 2718; project numbers BU 1335/12-1 and NU 265/5-1.)" reviewed acceptedVersion