Effects of task-relevance and intermodality change on electrodermal orienting and on processing resource allocation

The present study examined the effects of task-relevance of an habituation stimulus and intermodality change on electrodermal responses and on secondary task probe reaction time. In experimental conditions, subjects received 24 presentations of either a tone or a vibrotactile stimulus followed by one presentation of a stimulus From the other modality. Subjects in control conditions received 25 presentations of a tone or a vibration. Within each of these conditions, half the subjects were required to count the number of longer-than-usual stimuli which occurred with a probability of.25. Secondary task probes consisted of a visual stimulus of 500ms duration which, during habituation training, was presented 150, 300 or 600ms following stimulus onset and during some of the inter stimulus intervals. Trial 25 contained a probe at the 300ms position. The results indicated that skin conductance responses were not only larger on trial 25 in the experimental condition than in the control, but that they were larger than during the first half of the habituation series. In addition, reaction time was slower to within-stimulus probes in the task-relevant condition than to those presented in the task-irrelevant condition; was slower on trial 25 in the experimental condition than in the control, and, in the experimental condition, was slower on trial 25 than during the first half of the habituation series. The data are consistent with an information processing approach to orienting and habituation and appear to pose problems for non-comparator theories of habituation.