Speech is special: The stress effects of speech, noise, and silence during tasks requiring concentration.

Effects of noise on people depend on sound level but also on other sound properties. A systematic comparison of the stress effects of speech and noise with the same frequency content is missing. This study compared stress reactions under sound conditions speech (sound level 65 dB LAeq ), noise (65 dB), and silence (35 dB), all having similar relative frequency contents. Fifty-nine participants were exposed to one out of three sound conditions on average for 48 minutes while performing tasks requiring concentration. Acute physiological stress was estimated by measuring stress hormone concentrations in plasma (cortisol and noradrenaline), heart rate variability (HRV), and blood pressure. Psychological stress measures were subjective noise annoyance, workload, and fatigue. Compared to silence and noise, working during speech was more annoying, loading, but less tiring, and led to elevated HRV LF/HF ratio with time. Speech also raised cortisol levels compared with silence. Although noise was more annoying, and raised cortisol levels compared with silence, working during speech was more loading and caused more physiological stress than other sound conditions. Special care should be paid to noise control in workplaces requiring concentration because already exposure to moderate sound level sounds caused clear physiological effects on people.