Intertrial effects of same-different judgements

Specific intertrial effects (repetition effects) and general intertrial effects (refractoriness or persisting attention to the preceding trial) were studied with the same-different judgment task, which dissociates the effects of response repetition and stimulus repetition. Response repetition alone did not facilitate performance. Stimulus repetition did aid performance, but mainly when accompanied by response repetition. Subjects tended to avoid the normal comparison process by using the (invalid!) “bypass rule” (Fletcher and Rabbitt, 1978): repeat the response if the stimulus or some aspect thereof (letter contents, size, position) is repeated from the preceding trial, otherwise change the response. As to general effects, partial refractoriness was evident at response execution, but not at earlier processing stages. Mean RT increased, but errors decreased, as the response-stimulus interval (RSI) between trials decreased. Presenting a new letter pair immediately after the preceding response produced a delay, but subjects used the waiting time, while the response system recovered or was redirected to the present trial, to improve the accuracy of their decision.