Reaction times and error rates for judging nominal identity of letter strings

Most theories of “same”-“different” judgments predict that “same” responses should be at least as slow as “different” responses. However, the contrary has often been found. To explain this, a two-processor model has been proposed. In this model, a fast processor and a slow processor operate simultaneously. “Same” responses are initiated by whichever processor first indicates that the stimuli are “same,” whereas “different” responses are initiated only by the slow processor. In the experiment reported here, Ss judged whether two successively presented letter strings were nominally “same” or “different.” It was expected that the fast processor would be incapable of making nominal identity judgments. Thus, both “same” and “different” responses would be initiated by the slow processor. Consequently, “same” responses should have been slower than “different” responses. However, this did not occur. This finding casts doubt upon, but does not disprove, the two-processor model.