Mental multiplication and working memory

This paper is concerned with the role of working memory resources in mental multiplication. In two experiments a dual-task paradigm was used. In the first experiment neutral tapping was contrasted to three modality-specific secondary tasks: Irrelevant speech and articulatory suppression were used to disrupt the phonological loop and a visuo-spatial tapping was used to disrupt the visuo-spatial sketchpad. Multiplication sums needed to be solved mentally and results needed to be spoken aloud. Sums varied in difficulty (easy, e.g., 3 X 4 =, difficult, e.g., 8 X 17 =). Results from the first experiment revealed declines in performance on difficult sums under articulatory suppression but no interference effect for easy sums. To investigate the role of central executive processes, a second experiment extended the range of interference conditions to a central executive interference task (random letter generation). Now articulatory suppression and random generation caused a decrease of performance on difficult sums. In addition, performance on easy sums was negatively impacted by random letter generation as well. We infer that solving complex multiplication sums demands phonological loop and central executive processes, whereas retrieving numerical facts in solving simple multiplication sums requires only central executive processes. We found no evidence of modality-specific access to numerical facts stored in long-term memory.