ABSTRACT
Among the major contributions of T. C. Schneirla to current scientific thinking was his focus on approach and withdrawal processes, which were viewed as integrated behavioral patterns of evolutionary significance (e.g., Schneirla, 1939, 1959, 1965). Schneirla described approach and withdrawal as two distinct but interrelated processes influenced by the intensity of the stimulus. Approach processes involved movement toward stimulation, such as getting food or seeking warmth, with the associated activation of the parasympathetic branch of the autonomic nervous system (ANS)—heart rate deceleration, and more regular respiration and blood pressure. In contrast, withdrawal processes involved movement away from high intensity stimulation and were reflected in the activation of the sympathetic branch of the ANS and with heart rate acceleration and limb (e.g., arms, legs) muscular flexions. The biphasic approach and withdrawal processes were posited to act in opposition to one another, though both were viewed as significant in adaptive functioning in that they enabled the organism to respond flexibly to stimuli that were of variable intensity levels, and facilitated behaviors that were integral to the survival of species (e.g., obtaining food, avoiding danger, mating).
