Mental number representations are spatially mapped both by their magnitudes and ordinal positions

The Spatial-Numerical Association of Response Codes (SNARC) effect – i.e., faster responses to small numbers with the left compared to the right side and to large numbers with the right compared to the left side – suggests that numbers are associated with space. However, it remains unclear whether the SNARC effect evolves from a number’s magnitude or the ordinal position of a number in working memory. One problem is that in different paradigms the task demands influence the representational role of ordinality and magnitude. While the role of magnitude comes from single-task setups in which participants are making judgments about the parity of a displayed number, evidence for ordinal influences comes usually from experiments where ordinal sequences have to be memorized or setups in which participants possess pre-existing knowledge of the ordinality of stimuli. Therefore, in this preregistered study we employed a SNARC task, without secondary ordinal sequence memorization. We dissociate ordinal and magnitude accounts by careful manipulation of experimental stimulus sets. The results indicate that even though the observed data is better accounted for by the magnitude model, the ordinal position seems to matter as well. Hence, numbers are associated with space in both a magnitude- and an order-respective manner, yielding a mixture of both compatibility effects. Thus, a multiple coding framework may explain the roots of the SNARC effect most accurately.