Kicking the mental number line: a kinematic investigation of numerical processing in childhood.

A growing body of evidence in adults indicates bidirectional interactions between numerical processing and motor execution, often interpreted as the result of sensorimotor experiences linking numerical magnitude to physical size and action parameters. However, the developmental trajectory of number-action coupling, particularly for non-symbolic numerosities, remains largely unexplored. In the present study, we provide a developmental extension of a kinematic paradigm originally introduced in adults to investigate whether observing non-symbolic numerical stimuli modulates motor performance in preschool (4-6 years) and school-age (7-11 years) children. Using an engaging finger-kick task, we measured fine-grained kinematic parameters while children responded to small (2-Dots) or large (8-Dots) dot arrays, as well as to a non-numerical baseline stimulus. Preschoolers exhibited more efficient movement trajectories after observing small numerosities compared to the baseline condition, together with greater leftward trajectory deviations-consistent with a spatial-numerical mapping aligned with the Mental Number Line. In contrast, no kinematic modulation was observed following exposure to large numerosities, and no reliable numerical effects emerged in school-age children, mirroring patterns previously reported in adults. Taken together, these findings suggest that non-symbolic spatial-numerical mappings can directly influence action execution early in development, but may be reshaped or attenuated with increasing experience and formal education. By combining non-symbolic number processing with precise kinematic measures in children, the present study sheds light on early number-action links and their developmental reorganization, offering insights into the foundations of numerical cognition.