Hayman and Tulving (1989) reported a study on stem completion which shows some of the subtlety of implicit memory tests. Subjects studied lists of 160 words. These included 16 primacy fillers, 64 critical words, and 80 recency fillers. Subjects performed two fragment completion tests. The first test involved 32 words that the subject had studied plus 32 words not studied. The second test involved the other 32 studied words, 32 nonstudied words, plus whatever words the subjects had not successfully completed in the first test. These repeated words were either tested with the same fragment or a different fragment. For instance, if the original word was aardvark the two fragments were either a--d--rk or -ar-va--. Note the two are complementary.

ACT-R Model