Habituation of the orienting response as a function of arousal induced by three different tasks.

In order to investigate the extent to which habituation rate is influenced by the level of arousal, three consecutive experiments with 24 subjects each were carried out, involving the manipulation of arousal by a different task in every experiment. In Experiment I this was done by pressing a dynamometer; in Experiment II by remembering words; and in Experiment III by the instruction to react as quickly as possible to barely noticeable stimuli, which in fact were not presented. Although in all experiments arousal was clearly increased, at least as measured by the number of spontaneous electrodermal responses (EDR) and as indicated by the level of either skin conductance, or heart rate or pulse volume, habituation of the EDR was delayed only in Experiment III. Experiment I however showed a faster habituation rate, at least of the EEG and pulse volume reactions. The results of Experiment III were replicated in Experiment IV with 27 subjects. It was concluded that habituation is not a function of arousal but possibly of a variable criterion for the 'signal value' of the stimulus.