Sensorimotor numerosity uniquely supports arithmetic development in children

Symbolic numerical thinking is a signature human cognition, yet its foundations remain unclear. The prevailing perspective holds that numerical abilities build on a non-symbolic visual number sense that extracts numerosity from the environment. However, recent evidence suggests a sensorimotor number system also tracks the numerosity of internally self-generated actions. Whether this system supports the development of mathematical skills is unknown. In a series of psychophysical tasks, we measured precision (Weber fraction) for estimating, without counting, the number of (i) self-generated hand actions, (ii) visual-temporal flashes, and (iii) dot ensembles. Precision in the action-based numerosity estimation task explained about 30% of the variance in mental calculation ability - three and 15 times higher than spatial and temporal visual numerosity, respectively. This link remained strong even after regressing out the variance explained by natural development (age), verbal and non-verbal reasoning, non-numerical motor abilities, and visual numerosity estimation precision (R² ≈ 26%). These findings provide the first evidence for a specific link between the sensorimotor number system and mathematical competence, suggesting a foundational role of sensorimotor numerical processes in the development of symbolic human numerical cognition.