Placekeeping Ability as a Component of Fluid Intelligence: Not Just Working Memory Capacity

The question of what cognitive processes contribute to fluid intelligence (GO-the ability to solve novel problems-continues to be central in intelligence research. Here, we considered the contribution of placekeeping, which is the ability to perform a sequence of steps in a prescribed order without omissions or repetitions. Placekeeping plays a role in problem solving but also rests on the ability to remember past performance, so it may simply reduce to working memory capacity (WMC). To investigate this possibility, we evaluated whether placekeeping accounts for individual differences in Gf above and beyond WMC. Hierarchical regression analyses revealed that placekeeping ability accounted for 12% of the variance in Gf above and beyond WMC. By contrast, WMC accounted for only 2% of the variance in Gf above and beyond placekeeping ability. Structural equation modeling revealed that placekeeping ability and WMC are distinct at the latent variable level, and together they accounted for 77% of the variance in Gf. However, whereas placekeeping ability significantly predicted Gf in the structural equation model, WMC did not. In general, the results suggest that placekeeping ability is distinct from WMC and contributes substantially to individual differences in Gf.