Same digits, different magnitudes: manual reaching unveils dual systems in symbolic number representation

The role of Approximate Number System (ANS) in adult symbolic number processing remains controversial. Despite evidences for a linear and precise representation of symbolic numbers in adults, this study, based on Dual-Process Theory (DPT), proposes that ANS should still influence symbolic number processing in adults. To examine this possibility, we conducted two hand tracking experiments using a manual reaching numerical comparison task. In Experiment 1, we investigated differences in adults’ performances when comparing small numbers (#1–#9 vs. #5) and large numbers (91–99 vs. 95). The results showed that adults exhibited both higher response accuracy and greater deviation in movement trajectories when comparing small number pairs rather than large number pairs, indicating an implicit size effect in symbolic number representation. In Experiment 2, we ruled out the possibility that the results of Experiment 1 were driven by differences in visual format of stimuli (e.g., 9 vs. #9 vs. 09). Together, these findings provide consistent evidences for the implicit influence of ANS on adults’ symbolic number processing, unveiling the dual representations of symbolic numbers in adulthood and underscoring the potential of visuomotor tasks for probing implicit cognitive processing.