Counting on order: Order processing of numbers and mathematical ability in children and adults

Understanding the relationship between items – which is briefly called ordinality – has been shown to be strongly related to number processing skills and mathematical ability. Despite the growing interest in ordinality, it is still unclear which mechanisms underlie ordinality and why ordinality is related to mathematical ability. The overarching objective of this dissertation was to gain more insight in the strategies that children and adults use whilst processing different types of sequences and to examine its relation with mathematical ability. The studies presented throughout this dissertation systematically investigated the processing of different types of sequences in a digit order judgement task where participants have to indicate whether a presented sequence is in order or not. Additionally, the relation with mathematical ability was examined. Associative mechanisms and comparison mechanisms revealed to be two main strategies that are involved in order processing. However, which strategy is used is highly dependent on the context in which the task is presented. All the studies consistently found that ordinality is strongly related to mathematical ability although this relation could be largely explained by domain-general cognitive processes. From a developmental perspective, it was established that ordinality was not related to mathematical ability at the beginning of primary school. However, ordinality became increasingly important throughout development because children start to apply both associative and comparison mechanisms to process order and to perform arithmetic. Taken together, the results of this dissertation show why the ability to understand the relationship between items is an important fundament for mathematical ability. These new insights might have important implications for how we teach mathematics in school and how we can improve interventions targeting mathematical ability in children and adults.