A flexible vertical mental number line

There is general consensus that numbers are represented along with a culturally oriented left-to-right mental number line in Western cultures. Conversely, vertical number-space mappings may depend on cardinal (bottom-to-top) or ordinal (top-to-bottom) features. Here, participants’ self-reported counting habits and explicit preferences for visualizing and writing numbers vertically showed a strong top-to-bottom pattern. This explicit preference differs from the predominantly bottom-to-top Spatial–Numerical Associations (SNAs) reported in behavioural studies. These findings suggest that vertical number-space mappings are flexible and may depend on task context and the relative salience of ordinal and cardinal information. More broadly, these findings highlight the need to test whether theoretical accounts of SNAs, largely developed from evidence along with the horizontal axis, generalize to the vertical and sagittal axes.