Even Early Representations of Numerical Magnitude are Spatially Organized: Evidence for a Directional Magnitude Bias in Pre-Reading Preschoolers

Previous work has suggested that an important tool of adult numeric competence is a “mental number line” that codes increasing numeric magnitudes spatially and with a directional bias. Partly because the direction of this bias (leftto-right versus right-to-left) is culture-specific, it has been assumed that a directionally-biased mental number line is a late development. Our results, in contrast, suggest that nearly half of all preschoolers possess a directional magnitude bias and that those who possess this bias demonstrate competence in representing large numbers, a competence that is otherwise lacking in same-aged peers. Further, this directional bias does not appear to be related to pre-reading abilities, but instead seems to build on already existing preferences in counting direction.