EFFECTS OF INTERMODALITY CHANGE ON ELECTRODERMAL ORIENTING AND ON THEALLOCATION OF PROCESSING RESOURCES

Two experiments studied the effects of intermodality change on electro dermal responses and on reaction time to a secondary task probe stimul us after 24 habituation training trials with either a tone or a vibrot actile stimulus. The probe was a visual stimulus of 500 ms duration, a nd within-stimulus probes occurred 300 ms following stimulus onset. Ex periment 1 crossed change versus no change with modality of the traini ng stimulus. Skin conductance responses (SCRs) were larger in the expe rimental group than in the control on the test trial, and in the exper imental group, test trial responses were larger than those on the firs t training trial. Probe reaction time was slower on the test trial in the experimental group than in the control, and within-stimulus probe reaction time was slower than interstimulus interval reaction time ear ly in the habituation series. Experiment 2 crossed change versus no ch ange with the presence of a secondary task. Test trial SCRs were large r in the experimental group than in the control, regardless of whether or not the secondary task was present. In addition, test trial respon ses in the experimental group were larger than those on the first trai ning trial in both the task and no-task conditions. Within the task co ndition, reaction time was slower in the experimental condition than i n the control on the test trial. In addition, reaction time in the exp erimental condition was slower during the change trial than during the first training stimulus. The data provide difficulties for noncompara tor theories of habituation and seem to be most easily explained by th eories of habituation that emphasize the importance of an extrapolator y process.