The skin conductance orienting response as an index of attention.

In Experiment I 41 subjects performed one of three tasks while also hearing irrelevant tones tones. The three tasks were forewarned reaction time, vigilance and mental arithmetic and each was divided into discrete trials. The irrelevant tones either occurred during task performance (i.e., within a trial) or outside task performance (i.e., between trials). There was no difference in skin conductance OR magnitude to tones across the three tasks. Heart rate changes in contrast showed clear differences between tasks with a marked deceleration occurring during forewarned reaction time and a marked acceleration occurring during mental arithmetic. Skin conductance OR magnitude was significantly greater to tones occurring during task performance than to tones occurring outside task performance. This was interpreted as reflecting changes in the level of attention (higher during task performance) rather than direction of attention (away from tones during task performance). In Experiment II 39 subjects heard a series of irrelevant tones either while performing a forewarned reaction time task as in Experiment I or while performing no concomitant task. Rate of habituation was significantly faster for the subjects performing the concomitant task. This was interpreted as reflecting direction of attention which should be away from the tones when the subject was performing a concomitant task. Thus while rate of habituation to a class of stimuli may reflect direction of attention, short-term changes in OR amplitude probably reflect level of attention.