Voice monitoring to measure emotional load during short-term stress

Abstract.

It is well known that there is a relationship between the voice the human emotional status. Previous studies have demonstrated that changes of fundamental frequency (f ₀), in particular, have a significant relationship with emotional load. The aim of the present study was to investigate how f ₀ changes in response to an unknown emotionally stressful task under real-life conditions. A further question was whether repetitions of this task lead to an adaptation of f ₀, indicating a lower emotional load. The participants of this study included 26 healthy males. f ₀ and heart rate (f _c) were recorded for baseline testing (BLT) under relaxed laboratory conditions. Then the participants were asked to negotiate a natural obstacle by way of sliding down a rope hanging from a handlebar without any safety provisions, thus being exposed to the danger of a fall from a height of up to 12 m into shallow water (guerrilla slide I, GSI). The task was repeated after 30 min (GSII) and after 3 days of physical strain (GSIII). Immediately before starting the task the participants were asked to give a standardised speech sample, during which f _c was recorded. The mode value of f ₀ (f _0,mode) of the speech samples was used for further analysis. The mean (SD) value of f _0,mode at BLT was 114.9 (14.8) Hz; this increased to 138.8 (19.6) Hz at GSI (P<0.000), decreased to 135.9 (19.6) Hz at GSII and to 130.0 (21.5) Hz at GSIII (P=0.012). The increase in f _c was significantly different from BLT to GSI (P<0.000). The repetitions of the task did not produce significant changes in f _c. It was shown that f _0,mode is a sensitive parameter to describe changes in emotional load, at least in response to short-term psychoemotional stress, and seems to throw light upon the amount of adaptation caused by increased experience.