The unitary nature of Sokolov’s orienting response (OR) has been interpreted as requiring the covariation of a range of physiological indicators in response to stimulus variation. In contrast, Barry (1978) proposed a four-way fractionation of these indicators as a more realistic description of stimulus-response relationships in the OR domain. The first experiment tested aspects of this fractionation with simple visual stimulation and confirmed the existence of the three independent processes predicted for situations not requiring a motor response. Parallels between two of these processes and those of Groves and Thompson’s (1970) dual-process theory of habituation were noted, and then explored in the following two experiments. Results confirmed the fractionation obtained in the first experiment and indicated that dual-process theory can handle various aspects of response fractionation that cannot be accommodated by Sokolov’s OR theory. © 1981, Psychonomic Society, Inc.. All rights reserved.