EXPRESS: Spatial Biases in Arithmetic: The Effect of Operation Order and Visual Spacing on Calculations.

Visual layout is known to affect computational performance, yet its relation to response format and numerical proficiency remains unclear. This preregistered study examined whether spatial presentation modulates arithmetic problem-solving. We conceptually replicated Experiment 3 of Landy and Goldstone's (2010) study using the Precedence and Proximity Task in a forced-choice format. Additionally, we assessed arithmetic fluency using a speeded test. A total of 201 adults solved 200 mixed addition-multiplication expressions in which spacing either aligned or conflicted with order-of-operations rules. Operation order was also manipulated. Participants were faster and more accurate in congruent spacing conditions, whereas incongruent spacing increased operation-order errors, especially when problems began with addition. A subgroup of participants showed disproportionately poor performance under incongruent spacing, suggesting a prepotent susceptibility to misleading grouping cues. The spacing effect persisted despite differences in task format and response procedure compared to the original study, supporting its robustness. Higher arithmetic fluency was associated with higher accuracy and shorter reaction times in the Precedence and Proximity Task. These findings corroborate that visuospatial layout biases symbolic computation and that individuals differ in their susceptibility to it.