The freeze-like effects of arousal and valence on postural sway and heart rate

Abstract

When animals perceive threatening stimuli their defensive behaviour is activated. In a high vigilant state their showed immobility and decreased heart rate. Studies showed that these so called freeze responses are also found in humans, but the results show some inconstancies. To test whether and when freezing is present in humans, twenty healthy participants passively watched pictures while standing on a forceplate. The pictures were divided into five different categories: neutral, high arousal – pleasant, high arousal – unpleasant, low arousal – pleasant and low arousal – unpleasant. The participants’ heart rates were measured, and they filled out the NLETQ and STAI questionnaire. Results showed a decrease in heart rate when watching high arousal pictures, but no effect was found on postural sway. Despite the effects being moderate, these results indicate that arousal rather than valence influences freeze responses. The moderate effect could explain why no effect was found on postural data. Future research could focus on other stimuli which could elicit higher freeze responses to further investigate and to acquire more knowledge about when exactly freezing appears.