Unitary or non-unitary nature of working memory? Evidence from its relation to general fluid and crystallized intelligence

This study explored the controversy surrounding working memory: whether it is a unitary system providing general purpose resources or a more differentiated system with domain-specific sub-components. A total of 348 participants completed a set of 6 working memory tasks that systematically varied in storage target contents and type of information processing, as well as a set of 6 tests measuring general fluid intelligence and general crystallized intelligence. A structural equation modeling approach formalized and tested the theoretical expectations of the differentiation perspective on working memory. Visuo-spatial working memory was found to be more strongly correlated with general fluid intelligence than with general crystallized intelligence, and vice versa for verbal–numerical working memory. Additionally, general fluid intelligence was more strongly correlated with visuo-spatial working memory than with verbal–numerical working memory, and vice versa for general crystallized intelligence. These patterns of relationships supported the argument that working memory is not a simple unitary system, but can be differentiated in domain-specific components which are visuo-spatial working memory and verbal–numerical working memory.