Novelty detection and orienting: effects on skin conductance and heart rate.

In a repetition-change paradigm it was explored whether the skin conductance response (SCR) and the heart rate (HR) response similarly reflect involuntary and voluntary orienting. Seven orienting stimuli, consisting of six contextually novel stimuli and one novel change, were presented to 144 participants. In order to evoke voluntary orienting, the signal value of the contextually novel stimuli was manipulated by task instruction. Results suggest that the SCR is a manifestation of the involuntary orienting response (iOR). The HR, however, showed a non-uniform pattern of response and turned out to be susceptible to voluntary orienting. While it responded to the last orienting stimulus, the novel change, with a clear-cut deceleration, the response to the first orienting stimulus had a polyphase structure and was sensitive to repetition and signal value. The HR response is, thus, of limited value as an indicator of the iOR because of its striking susceptibility to voluntary orienting.