Repeated exposure to exemplars does not enhance implicit learning: A puzzle for models of learning and memory.

We learn regularities in the world around us, frequently without conscious effort, a phenomenon known as implicit learning. These regularities are often impossible to verbalise. One example of implicit learning is the structural effect, in which participants learn a rule set combining two factors, such as lexical frequency and concreteness. Theories of implicit learning predict that repetition of exemplar words would result in improved learning of the rule set, increasing the magnitude of the structural effect. Over four experiments, we demonstrate that this is, in fact, not the case. In Experiments 1 and 2, three repetitions of exemplar words result in superior item memory, but no change in the magnitude of the structural effect, compared with individually presented words. In Experiments 3 and 4, the structural effect is shown to be invariant to five repetitions of exemplar words and at high and low numbers of exemplars. In all four experiments, participants were unable to describe the rule set underlying the structural effect. However, confidence ratings demonstrated sensitivity to the structure and this sensitivity, unlike endorsements, increased with strength. The results are discussed in reference to differentiation, structural versus judgement knowledge, and flexible learning systems.