The effects of stimulus similarity on frequency judgments of presented andnonpresented words

Global memory models predict that performance in frequency discrimination s hould be influenced by the total similarity of each test stimulus to the st udy list items. This effect of total similarity should hold for test items that were never presented on the list as well as for test items that were o n the list. Three experiments that test this prediction are reported. All t hree experiments tested performance on null trials, where subjects were ask ed to discriminate between items of equal objective frequencies. The predic tions of the global memory models were supported. However, when subjects we re given two study-test phases, they showed a negative-similarity effect on studied items that were presented in the second phase.