Distinguishing among Orienting, Defense, and Startle Reflexes

Abstract

Orienting reflex (OR) theory stresses the existence of two generalized systems that share many components but have opposite effects on sensitivity to stimulation. The OR is said to enhance sensitivity and the defensive reflex to reduce it. This chapter summarizes the evidence indicating that direction of heart rate change distinguishes between orienting and defense systems when criteria derived from Sokolov are applied. It discusses the evidence that startle constitutes a third reflex system that can be distinguished from both orienting and defense. The effects of stimulus rise time on the direction of short-latency cardiac changes is an example of such a qualitative difference. The chapter suggests that three aspects of stimulation—transient change, sustained intensity, and information—produce distinguishable reactions that can be associated, respectively, with startle, defense, and orienting reflexes and can be indexed by the latency and direction of cardiac rate changes.