Joint Processing of Arrow Direction and Number Magnitude Strengthens Spatial-Numerical Associations: Evidence from a Modified Flanker Task

The existence of a conceptual link between numbers and space is a fundamental question in numerical cognition and has been highly debated in recent years. Although Spatial-Numerical Associations (SNAs) have traditionally been investigated using bimanual response settings, recent studies have moved towards unimanual paradigms to avoid potential measurement artifacts. For instance, an influential line of research adopted a modified Implicit Association Test (IAT) in which numbers and arrows were presented sequentially. However, SNAs consistently emerged only when spatial and magnitude codes were explicitly contrasted, questioning the idea that numbers are inherently represented in a spatial format. To further investigate this issue, we designed a modified flanker task in which spatial and numerical stimuli were presented simultaneously. When arrows were task irrelevant (Experiment 1), no significant SNA emerged. By contrast, when participants judged arrow direction and numerical magnitude conjunctively (Experiment 2), the paradigm revealed extremely large SNAs compared to existing literature. Overall, our results provide no evidence for a purely conceptual spatial–numerical link, suggesting that robust SNAs require explicit spatial codes combined with semantic number processing. Finally, the large effect size of group-level SNAs, together with remarkable mixed-model-derived psychometric properties, indicates the modified flanker task as an ideal paradigm for studying individual differences and effect modulations. We suggest that this paradigm has the potential to further advance the research on SNAs by overcoming limitations of previous bimanual and unimanual paradigms and, consequently, by helping to disambiguate mixed results in the literature.