Decomposing SNARC: How distinct spatial-numerical association components relate to specific early numerical skills in...

The SNARC effect (Spatial-Numerical Association of Response Codes) is the most extensively studied spatial-numerical association, referring to faster left- and right-sided responses to small and large numbers, respectively. However, evidence for a relation between the SNARC effect and mathematical performance remains inconclusive. Several factors may explain these inconsistencies. First, they may arise from how the SNARC effect is typically computed. Conventional analyses use a single regression slope linking numerical magnitude and spatial response, thereby conflating two dimensions: the directionality (left-right polarity) and the size of the association, which may differentially relate to mathematical performance and should be examined separately. Moreover, intra-individual variability in SNARC estimates introduces imprecision that can obscure meaningful relations. Second, different mathematical skills may engage spatial-numerical processes to varying degrees. Accounting for this is essential to clarify the nature of the SNARC-math relation, particularly in younger children when early mathematical skills are first emerging. To address these issues, we examined the SNARC effect in 135 kindergarteners using a magnitude judgment task (i.e., a speeded task in which participants judge whether centrally presented Arabic digits are smaller or larger than a reference value), deriving three indices characterising the SNARC slope: absolute size, directionality, and intra-individual variability. Early numerical skills were assessed through counting, numerosity comparison, magnitude judgment and ordinal judgment tasks. Traditional SNARC slopes did not correlate with mathematical performance, but regression analyses separating size, directionality, and variability revealed distinct effects: intra-individual variability predicted magnitude judgment, whereas directionality predicted ordinal judgment. These findings indicate that decomposing the SNARC effect and accounting for intra-individual variability reveals meaningful, task-specific associations, offering a potential explanation for previous inconsistencies.