What does it take to implicitly prime low-frequency category exemplars?

Prominent views of implicit priming agree that repetition of category exemplars should increase the probability of the exemplar coming to mind on a category production test. This prediction has been borne out in the data of numerous experiments that have used relatively high-frequency exemplars, but experiments that have used lower frequency exemplars have reported reduced or no priming on category production tests. Frameworks of memory disagree on why frequency would affect priming. The authors report 3 experiments, the first of which shows no priming of low-frequency exemplars under circumstances that yield priming of higher frequency instances. The second 2 experiments show that low-frequency instances can be primed, but the prior experience must bias the comprehension of the category label, not the exemplar.