Dissociations of grammaticality and specific similarity effects in artificial grammar learning.

Three artificial grammer learning experiments investigated the memory processes underlying classification judgments. In Experiment 1, effects of grammatically, specific item similarity, and chunk frequency were analogous between classification and recognition tasks. In Experiments 2A and 2B, instructions to exclude "old" and "similar" test items, under conditions that limited the role of conscious recollection, dissociated grammaticality and similarity effects in classification. Dividing attention at test also produced a dissociation in Experiment 3. It is concluded that a dual-process model of classification, whereby the grammaticality and specific similarity effects are based mostly on automatic and intentional memory processes, respectively, is consistent with the results, whereas a unitary mechanism account is not. This conclusion is further supported by evidence indicating that chunk frequency had both implicit and explicit influences on classification judgments.