Blocking as a friend of induction in verbal category learning.

We conducted an experiment to investigate the influences of interleaved versus blocked presentation of disparate verbal exemplars on the induction of category concepts. The practice schedules of four experimental groups were juxtaposed such that sets of exemplar-category associations were either solved in succession (i.e., blocked), systematically intermixed (i.e., interleaved), or presented with an incremental transition from blocked to interleaved practice. Counter to current trends in the literature, in which interleaving alone has been facilitative of induction in some tasks, we found that participants whose initial exposure to the category exemplars involved blocked presentation performed better in both implicit and explicit tests of concept learning. The results are discussed with respect to the impacts of task type, task difficulty, and exemplar relatedness on induction.