EFFECTS OF STIMULUS PREEXPOSURE AND INTERMODALITY CHANGE ON ELECTRODERMAL ORIENTING

Previous research has indicated that an intermodality change trial pre sented after a habituation series elicits larger orienting responses t han does the first stimulus of that series. Experiment 1 (N = 48) inve stigated whether this effect was still present if the change stimulus was not novel but was presented once prior to the habituation series. Two groups of subjects were presented with a series of 24 tones or vib rotactile stimuli. Trial 25 was an intermodality change test trial for half of the subjects in each group (change), whereas the remaining su bjects received an additional habituation stimulus (no change). Prior to the habituation trials, each subject was exposed once to the test s timulus used in the change condition. Although response magnitude on t he test trial was larger in the change condition than in the no-change condition, test trial response magnitude did not exceed that on the f irst trial of the habituation series. In Experiment 2 (N = 84), one gr oup was preexposed to the test stimulus, another was pre exposed to an experimentally irrelevant stimulus, and a third received no stimulus prior to habituation training. Test trial response magnitude was large r than responses to the first stimulus of habituation in the change gr oup that was not exposed to a stimulus prior to habituation but not in the preexposed groups. Preexposure to a stimulus prior to habituation training abolished the intermodality change effect even when the test stimulus was novel. The present results pose problems for noncomparat or theories of habituation and support the notion that anticipatory pr ocesses are important in orienting and habituation.