The structure of individual differences in procedural working memory: Comparing task switching and stimulus response rule information load

Working memory (WM) serves not just for remembering facts (“declarative WM”) but also for controlling action and thought (“procedural WM”, pWM) by holding and manipulating task rules and task control parameters such as goals. Yet, the structure of individual differences in pWM is underexplored. The present work compared between two highly similar (in the number of stimulus response rules, stimuli, responses, and scoring method) pWM challenges: Rule WM (rWM) - loading WM with novel arbitrary stimulus response rules, and Task switching between familiar rules. A series of confirmatory bi-factor models fitted to results from two separate highly variable samples (N = 544, 520) support the existence of a common (to Switching and rWM) ability as well as the distinction between rWM and Switching. Latent regression models in which correlated latent variables of Switching, Speed and rWM predicted Reasoning and Anti-saccade performance indicate a different pattern of variance sharing for switching and rWM: Specific rWM and the rWM-Speed variance overlap predicted Reasoning, whereas specific Switch did not. Switch was predictive of Anti-saccade and Reasoning only through its overlap with the rWM (for Reasoning) and with both Speed and rWM (for both outcomes). Together, these results support the conclusion that the ability to meet a switching challenge and the ability to meet a challenge of having many rules to remember (rWM) constitute partly separable sources of individual differences.