Artificial grammar learning (AGL) experiments are commonly used to assess implicit learning. However, in these tasks participants may acquire explicit rather than implicit knowledge. We combined an AGL task with measures of metacognition to assess whether participants acquired explicit knowledge of the grammar. Participants were initially exposed to sequences of visual symbols generated by an artificial grammar, followed by a testing phase in which they classified sequences as either grammatical or ungrammatical. On a subset of trials (choice trials) participants were given the option to either take or skip this classification. If participants had explicit knowledge of the grammar, they should be more likely to take trials when they are confident and skip when they are not. Participants learned the grammar and reported explicit knowledge of the grammar. However, they performed similarly in forced and choice trials, suggesting that this metacognitive measure does not measure the explicitness of their knowledge of this grammar.

Comparative sequence learning experiments allow cognitive processes that are required for language in humans to be studied in nonhuman animals. We investigated Rhesus macaques’ ability to detect abstract regularities in visual sequences, and their capacity to generalize to novel stimuli. On each trial, two colors were randomly generated and arranged into three-element long sequences based on three rules (‘AAB’, ‘ABA’, ‘BAA’). Monkeys were able to learn the rules and select appropriate sequences of colored squares, and generalized this learning to the novel color combinations. To further assess generalization, we presented probe trials using sequences comprised of randomly generated white shapes. Monkeys showed no evidence of spontaneous generalization between stimulus categories. Our results demonstrate that monkeys are able to learn abstract rules governing visual sequences and that they generalize these to novel sequences within a stimulus category, but provides no evidence of generalization between stimulus categories.