The role of verbal working memory load on number order processing: Evidence from an articulatory suppression paradigm

Although number order processing has received increasing research attention due to its association with arithmetic skills, its underlying cognitive mechanisms remain unclear. It has been suggested that highly familiar sequences (e.g., 1-2-3, 2-4-6) are processed faster because they are retrieved from memory. However, the involvement of verbal memory retrieval has not been directly tested and is usually inferred indirectly from participants' response times. In this study, participants completed an order verification task standalone and under verbal working memory load involving articulatory suppression, where participants repeated the syllables "pa-ta-ka" throughout the task. Participants also completed arithmetic production and verification tasks to evaluate the association between order processing and arithmetic. As expected, verbal working memory load increased response times, but this effect was stronger for consecutive than non-consecutive sequences, rather than for familiar versus unfamiliar ones as initially hypothesised. This pattern suggests that articulatory suppression may disrupt sub-vocal routines such as internal counting, which may be more prominent in consecutive sequences compared to non-consecutive, although familiar, sequences. Nevertheless, a robust familiarity effect was observed overall, with familiar sequences processed faster than unfamiliar ones. These findings point to a general involvement of verbal working memory in number order processing, particularly in relation to sequences that align with common counting routines. Finally, order verification performance was more strongly associated with arithmetic production for small problems-likely reflecting greater reliance on memory retrieval-and showed trends toward stronger associations with arithmetic verification and familiar sequences.