Effects of Stimulus Intensity on Autonomic Responding: The Problem of Differentiating Orienting and Defense Reflexes

Abstract

Psychophysiological research has frequently applied autonomic measures as indices of information processing. One rationale which underlies this approach is the distinction between orienting (OR) and defense reflexes (DR). Sokolov (1963) proposed that elicitation of these reflexes depends upon the intensity of the stimulus. He also suggested that ORs and DRs could be differentiated both in terms of their consequences for information processing and by their component autonomic reactions. Evidence in support of Sokolov's model is reviewed, and a series of experiments are described which were designed to demonstrate the effects of auditory stimulus intensity on autonomic responding. On the basis of these observations, a revised scheme of OR/DR differentiation is put forward. The major features of the scheme are the response direction of the autonomic measures, the identification of short‐ and long‐latency response components, and the inclusion of the startle reflex. The implications of the revised scheme for research on autonomic responses to affective stimulation are discussed. It is concluded that the sole use of autonomic measures to index information processing is inadequate. Consequently, future research requires both autonomic indices and behavioral and subjective measures of affective and information processing.