EXPRESS: Ordinality: The importance of its trial list composition and examining its relation with adults' arithmetic and mathematical reasoning.

Understanding whether a sequence is presented in an order or not (i.e. ordinality) is a robust predictor of adults' arithmetic performance, but the mechanisms underlying this skill and its relationship with mathematics remain unclear. In this study, we examined: a) the cognitive strategies involved in ordinality inferred from behavioural effects observed in different types of sequences and b) whether ordinality is also related to mathematical reasoning besides arithmetic. In Experiment 1, participants performed an arithmetic, a mathematical reasoning test and an order task, which had balanced trials on the basis of: order, direction, regularity and distance. We observed standard distance effects (DEs) for ordered and non-ordered sequences, which suggests reliance on magnitude comparison strategies. This contradicts past studies that reported reversed distance effects (RDEs) for some types of sequences, which suggest reliance on retrieval strategies. Also, we found that ordinality predicted arithmetic but not mathematical reasoning when controlling for fluid intelligence. In Experiment 2, we investigated whether the aforementioned absence of RDEs was because of our trial list composition. Participants performed two order tasks; in both tasks no RDE was found demonstrating the fragility of the RDE. Additionally, results showed that the strategies used when processing ordinality were modulated by the trial list composition and presentation order of the tasks. Altogether, these findings reveal that ordinality is strongly related to arithmetic and that the strategies used when processing ordinality are highly dependent on the context in which the task is presented.