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Hearing, Sound, Noise, and Vibration
Published in R. S. Bridger, Introduction to Human Factors and Ergonomics, 2017
The startle reaction generated by unexpected auditory stimuli is common to all mammals (Valle-Sole et al., 1995) and originates from the brain stem (Brown et al., 1991). It is thought to be an adaptive response that results in the rapid adoption of a defensive stance with maximum postural stability. The eyes close, the neck flexes, and the shoulders abduct with pronation of the forearms and clenching of the fists. The torso flexes forward and the knees flex. Auditory stimuli are powerful producers of the startle response. The ergonomic relevance is that startle interferes with task performance and slows reaction time for other tasks. Startle is elicited by loud noises of about 100 dB with a rise time of 5 ms (Matsumoto and Hallet, 1994). In the short term, operators will habituate to startling auditory stimuli after four or five exposures or over the course of a few minutes. Auditory stimuli with fast onset times have the advantage of being very attention getting but Sorkin (1987) cautions against onset rates of more than 10 dB/ms. For auditory stimuli to be alerting, but not startling, onset rates of 1 dB/ms are recommended. Sudden loud noises can have serious health consequences for sensitive individuals such as “startle epileptics” where they may trigger a seizure. Posttraumatic stress sufferers may exhibit an exaggerated startle response that is easily triggered.
Distraction for the eye and ear
Published in Theoretical Issues in Ergonomics Science, 2020
Philip Morgan, Bill Macken, Alexander Toet, Aline Bompas, Mark Bray, Simon Rushton, Dylan Jones
Aversive states or environments may increase the startle response (see Grillon and Baas 2003). More generally, the magnitude of the startle response can be increased in the presence of stimuli or environments with which the participant has learned to associate fear, or negative emotion (e.g. Grillon and Davis 1997). The mere threat of an aversive stimulus evokes this fear-potentiated-startle-response (Baas et al. 2002).