What factors contribute to subjective experiences of familiarity, and are these subject to unconscious selection? We investigated the circumstances under which judgments of familiarity are sensitive to task-irrelevant sources using the artificial grammar learning paradigm, a task known to be heavily reliant on familiarity-based responding. In 2 experiments, we manipulated ‘free-floating feelings of familiarity’ by subliminally priming participants with either a subjectively familiar stimulus (their surname) or unfamiliar stimulus (a random letter string). In Experiment 1, after training on an artificial grammar, participants were required to rate the familiarity of a new set of grammar strings where the subliminal priming manipulation preceded each rating. Under these instructions the manipulation significantly altered ratings of familiarity. In Experiment 2, the training, the request for familiarity ratings, and the subliminal manipulation were all unchanged. In addition, however, participants were informed about the presence of rules dictating the structure of the training strings and were required to judge both whether each test-string conformed to those rules and to report the basis for their judgment. This broader decision context eliminated the effect of subliminal primes on ratings of familiarity even when participants’ reported basis for their judgments revealed no conscious knowledge of the rule structure. These results demonstrate that unconscious sources of familiarity can be selected or excluded according to conscious task contexts. The findings are incompatible with theories that equate familiarity with automaticity and those that state people must always be aware of the structural antecedents of metacognition.