The effects of anticipated information on skin conductance and cardiac activity.

This experiment examined electrodermal and cardiac activity within a two-stimulus anticipation paradigm. A warning stimulus informed subjects (N = 24) whether an imperative stimulus to follow would contain two or four letters (low or high information conditions) and whether this stimulus would be presented for 60 or 75 msec (short or long duration). The subject's task was to identify as many of the letters in the imperative stimulus as possible. Although the amount of information conveyed by the warning stimulus was identical throughout the experiment (2 bits), skin conductance responses during the warning stimulus-imperative stimulus interval were larger prior to the high information imperative stimulus than prior to the low. Cardiac activity was not affected by the experimental manipulations. The implications of these findings for theories of the orienting response are discussed, particularly with reference to the view that orienting reflects an activation of the information processing system.