Procedural and Declarative Knowledge Simultaneously Contribute to Category Response Selection

Skilled behaviour in real-world contexts often relies on a combination of both declarativeand procedural learning. However, precisely how declarative and procedural knowledge interactis not yet fully understood. Previous findings have shown that procedural and declarativelearning may interact or compete at the systems level during encoding, consolidation, andretrieval, but beyond this, it is not known whether declarative and procedural representationsthemselves interact. The goal of the current study is to investigate whether procedural anddeclarative knowledge can contribute simultaneously to categorization response selectionbehavior. We designed a stimulus set in which information learned by each system sometimessupports different responses, and created trials in the test phase that are designed to maximizesuch divergence. Participants were instructed to use a completely diagnostic, verbalizable, shape-based rule to categorize exemplars, receiving feedback after each trial. However, unbeknownst toparticipants, the categories also differed probabilistically in their color distributions. Participantsused both color (learned procedurally) and shape (learned declaratively) to categorize exemplars,responding more quickly when both sources indicated the same category judgement, and moreslowly when they conflicted. Debriefing confirmed that most participants were unaware of thecolor distributions. These results show simultaneous trial-level contributions from bothdeclarative and procedural memory systems. Our findings represent a novel form of interactionbetween the two systems and have implications for domains beyond the laboratory, such asdecision-making and classroom instruction.