The domain specificity of working memory is a matter of ability

The relative importance of domain-general and domain-specific sources of variance in working memory capacity (WMC) is a matter of debate. In intelligence research, the question of domain-generality is informed by differentiation: the phenomenon that the size of across-domain correlations is inversely related to ability: the lower the ability, the more domain-general the variance. Since WMC and intelligence are related constructs, differentiation might exist in WMC, too. Differentiation in WMC is also predicted by process overlap theory, a recent model of intelligence. We used moderated factor analysis to test for differentiation. The results demonstrate the existence of differentiation in WMC: as capacity increases, variance in WMC becomes more domain-specific. Fluid reasoning (Gf) also contributes to differentiation in WMC: when Gf is lower, WMC variance is more domain-general. There was no significant moderation by crystallized (Gc) and spatial (Gv) ability and Gf only moderated differentiation in WMC but not in short-term memory.