Motion-numerical compatibility affects magnitude classification

Number concepts are spatially organized along a mental-number line (MNL) with smaller magnitudes represented in left/lower space and larger magnitudes progressively toward right/upper space. Evidence for this association largely relies on simple button responses. We investigated the generality of this association with directional head movements. In a preliminary test, 31 neurotypical adults classified spoken numbers with lateralized buttons faster under MNL-congruent than incongruent conditions along both horizontal and vertical axes. Having established the standard number-space association, participants then performed a Go/No-go version of our task with concurrent horizontal or vertical head movements. The results showed a congruency effect between number magnitude and head direction—which was limited to the horizontal axis. Our results suggest that horizontal motion induces spatial attention shifts which facilitate spatially congruent magnitude processing, thus supporting a conceptual association of space and magnitude.