Evidence that learning rule-based (RB) and information-integration (II) category structures can be dissociated across different experimental variables has been used to support the view that such learning is supported by multiple learning systems. Across 4 experiments, we examined the effects of 2 variables, the delay between response and feedback and the informativeness of feedback, which had previously been shown to dissociate learning of the 2 types of category structure. Our aim was twofold: first, to determine whether these dissociations meet the more stringent inferential criteria of state-trace analysis and, second, to determine the conditions under which they can be observed. Experiment 1 confirmed that a mask-filled feedback delay dissociated the learning of RB and II category structures with minimally informative (yes/no) feedback and also met the state-trace criteria for the involvement of multiple latent variables. Experiment 2 showed that this effect is eliminated when a less similar, fixed pattern mask is presented in the interval between response and feedback. Experiment 3 showed that the selective effect of feedback delay on II learning is reduced with fully informative feedback (in which the correct category is specified after an incorrect response) and that feedback type did not dissociate RB and II learning. Experiment 4 extended the results of Experiment 2, showing that the differential effect of feedback delay is eliminated when a fixed pattern mask is used. These results pose important challenges to models of category learning, and we discuss their implications for multiple learning system models and their alternatives. (Contains 2 tables, 10 figures and 9 footnotes.)