Why is working memory related to intelligence? Different contributions from storage and processing.

Domain-specific contributions of working memory (WM), short-term memory (STM), and executive functioning (EF) to individual differences in intelligence were analysed using a latent variable approach. A sample of 345 participants completed a battery of 24 tests tapping the constructs of interests as comprehensively as possible. Visuospatial and verbal STM and WM tasks were administered along with three subcomponents of EF, namely inhibition, planning, and shifting. Intelligence was assessed by non-verbal/abstract/fluid intelligence (Gf) and verbal/crystallised intelligence (Gc) standardised tests. Structural equation modelling results show that EF is the main predictor of Gf, whereas verbal STM is the main predictor of Gc. Storage and processing providing different contributions to the prediction of Gf and Gc supports the view that both short-term storage and executive functioning account for the relationship between WM and intelligence. This main conclusion stresses the importance of acknowledging core cognitive constructs as being hierarchical systems with general and domain-specific mechanisms.