Effects of intermodality change and number of training trials on electrodermal orienting and on the allocation of processing resources.

The present experiments examined the hypothesis that the electrodermal orienting response elicited by and the processing resources allocated to an intermodality change stimulus will vary as a function of the amount of pre-change habituation training. Experiment 1 (N = 64) employed a 2 x 2 design in which subjects received either 6 or 24 training trials followed by either an intermodality change trial or a further trial with the training stimulus. Skin conductance responses were measured throughout. Training and test stimuli (visual and vibrotactile) were counterbalanced within groups. Intermodality change elicited larger responses than did no-change, and in the 24-trial condition, test trial responses were larger than those on trial 1 of the habituation series. Experiment 2 (N = 64) employed the same design and procedure except that reaction time to auditory probes presented 300 ms following the onset of some stimuli and during some of the intertrial intervals was also measured. The results indicated that in the 24-trial condition, but not in the 6-trial condition, probe reaction time on the test trial was slower in the Change group than in the No Change group. Probe reaction time on the test trial did not exceed reaction time on the first trial of habituation. The results are consistent with the view that development of a stimulus expectancy is one important factor in producing the intermodality change effect.