An Examination of the Orienting and Defensive Responses Using HR and HF-HRV

Abstract: Psychophysiological researchers have demonstrated that the orienting response is characterized by heart rate (HR) decreases and high-frequency heart rate variability (HF-HRV) increases. The defensive response is characterized by HR increases and HF-HRV decreases. In this study, HR and HF-HRV reactivity to a visual stimulus designed to elicit an orienting response (surgery video) and a cognitive task designed to elicit a defensive response (Trier Social Stress Test, math task) were measured among 81 undergraduate students. The order of stimuli presentation was counterbalanced. The expected pattern of reactivity was observed (decreased HR and increased HF-HRV during the video condition; increased HR and decreased HF-HRV during the cognitive math task). The order of stimulus presentation significantly influenced HF-HRV reactivity. When the video stimulus was presented first, a large and significant increase in HF-HRV was observed which indicated vagal activation. When the video stimulus followed the cognitive math task stimulus, lower levels of HF-HRV reactivity and vagal activation were observed. This suggests exposure to the cognitive math task elicited a defensive response that suppressed subsequent orienting responses. Theoretical, psychophysiological, and practical implications of the observed results and future psychophysiological research directions are discussed.