Investigating the effects of magnitude-space based numerical working memory loads on the SNARC effect under different number judgment tasks.

The Spatial-Numerical Association of Response Codes (SNARC) effect refers to the phenomenon where smaller numbers are associated with faster left-side responses and larger numbers with faster right-side responses. Previous working memory (WM) research on the SNARC effect has examined cognitive load using visuo-spatial and phonological tasks, highlighting the effect's flexibility. This study investigated the effects of mental number line (MNL) compatibility (small-left/large-right vs. small-right/large-left) and magnitude-space-based cognitive loads (space, magnitude, and magnitude-space) on number judgments. Participants completed a numerical 1-back task involving three types of WM loads presented in either MNL compatible or incompatible formats. Responses to targets were made based on whether a number matched the spatial position (space load), magnitude category (magnitude load), or both (magnitude-space load) of the preceding number. After each 1-back evaluation, participants performed either a single parity judgment (odd/even) or magnitude comparison (smaller/larger than 5). The results showed that MNL compatible conditions produced a regular SNARC effect, while incompatible conditions led to a reverse SNARC. The effect was more pronounced under the space load than under the magnitude load. In parity judgment, compatible loads produced a regular SNARC effect, whereas incompatible loads showed no reverse SNARC. In contrast, the magnitude comparison task revealed a more pronounced reverse SNARC under incompatible loads. These results challenge the SNARC effect as purely automatic, emphasizing the coactivation of long-term numerical representations and WM in shaping spatial-numerical associations. Furthermore, the findings highlight the effect's sensitivity to task-specific demands, demonstrating that spatial-numerical associations can dynamically adapt to varying cognitive strategies.