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Title: Auditory fitness for duty : acoustic stealth awareness
Author: Blyth, Matthew
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2019
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Military personnel sometimes have to operate without being detected. In these situations, it is important that the individual has an awareness of their own detectability, both visually and acoustically, in order to operate effectively. Acoustic stealth awareness (ASA) refers to an individual’s judgement of their aural detectability with respect to a detector (target). It has been suggested that hearing impairment might affect ASA due to reduced auditory feedback; however, there has been very little research on ASA, including how to measure it and the factors that influence it. Given the potential implications of hearing impairment for an individual’s auditory fitness for duty (AFFD), a better understanding of the role of hearing in ASA and how hearing impairment impacts an individual’s AFFD is required. The aim of this study was to develop a method for investigating ASA, explore factors that affect judgements and assess the accuracy of judgements. A number of potential experimental approaches were considered to balance the need to control variables that might influence ASA (background noise, wind noise, etc.) and ecological validity. Experiment 1 investigated egocentric visual distance estimation in virtual reality (VR) and reality in an outdoor open field environment. The results showed that distance estimation was similar on average in the two viewing environments over 25 – 125 m. This suggested that VR could be used in applications where similar distance estimation to reality over these ranges is likely to be important, such as ASA. Using the same VR environment as for Experiment 1, a novel method for measuring aural detectability judgements was developed. This required subjects to: 1) view a distant target, 2) listen to a sound produced near them, and 3) judge, yes or no, whether the target would be able to detect that sound. Experiment 2 used this developed method to investigate aural detectability judgements for various subject-target distances (25, 50, 100 m) and stimulus types (Gaussian noise, pine cone crunching, whispered digits), measured using normal-hearing civilians. The results showed that judgements were repeatable, sensitive to sound level, sensitive to subject-target distance and dependent on the stimulus type. Experiment 3 measured the absolute thresholds for each of the sounds that people judged in the previous experiment. The results of these two experiments were combined in order to assess the accuracy of aural detectability judgements. In general, people did not make accurate judgements, rather subjects tended to report sounds as undetectable when they probably were detectable. Judgements were found to get less accurate as subject-target distance increased, and were markedly poorer for whispered digits, suggesting that prior experience of sounds might affect judgements. It is concluded that aural detectability judgements are sensitive to relevant factors such as distance and sound level, but are generally inaccurate, at least for normal-hearing civilians; the degree of error associated with judgements is variable between people, but mostly in the direction that suggests people do not have accurate ASA. This may have implications for the military; further research is required in order to understand if these findings are replicated by military personnel and in real-life acoustic stealth situations, and how hearing impairment affects judgements.
Supervisor: Rowan, Daniel Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available