Seeing the fours before the threes: investigating numerical signatures with hierarchical navon stimuli

When two numbers are compared, numerical processing signatures include the size effect (small numbers processed faster than large ones), the Spatial-Numerical Association of Response Codes (SNARC) effect (small numbers classified faster with left side than right side responses), and the distance effect (numbers farther from a reference processed faster than those closer). These signatures reflect single digit processing and their relevance for multi-digit processing relies on evidence from horizontal digit strings. In hierarchical displays, such as Navon stimuli, different information coexists at various spatial scales (local and global). Consequently, a single stimulus supports different processes depending on the attended scale. We examined number processing at two different spatial scales to investigate the influence of both the task relevant and irrelevant digits on processing signatures. We used hierarchical stimuli with symbolic numbers (1, 4, 6, 9) at global and local levels, such as a large "global" digit (e.g., 9) composed of smaller "local" digits (e.g., 1). Separate groups of participants classified either the global (N = 31) or local (N = 30) number magnitude relative to 5, ignoring the other scale. Consistent with Navon effects, we found faster processing for global than local stimuli and when global and local information matched. Both groups demonstrated significant SNARC and distance effects, but only the local group showed size effects. Notably, local numbers were classified faster even when the global number required the same response. Overall, these results indicate that numerical processing operates concurrently at different spatial scales, though local information is particularly vulnerable to interference from global context. This underscores the complex interplay between global and local processing in numerical cognition.