On the plasticity of sound localization during the use of hearing protection devices

Abstract

Hearing is important for communication and situational awareness. Hearing loss due to noise exposure or other insults can degrade these capacities, with corresponding impacts on quality of life and occupational fitness. High-intensity acoustic signals are commonplace in a variety of occupational settings (e.g., military, construction, manufacturing) and are a major cause of permanent hearing loss. Hearing protection devices (HPDs) are therefore essential personal safety equipment for those operating in noisy environments, and are widely available, often in concert with organizational hearing conservation programs that support their use. However, HPDs can exert undesirable perceptual side effects, including acute disruption of spatial hearing. As HPDs are placed in and around the ears, distortions of the natural pinna-related spatial cues result, leading to decreased sound localization abilities, device dissatisfaction and disuse. This dissertation is comprised of three studies that investigate both the impact of hearing protector use on sound localization abilities and the capacity for recovery of those abilities with user training. The first study assessed the horizontal localization abilities of subjects before and after adapting to degraded spatial cues via earplugs. Over the course of eight weeks with intermittent training, subjects demonstrated a vastly improved ability to localize sound sources across both the front and rear hemifields, especially for subjects receiving audiovisual feedback during training. Expanding on these results, the second study aimed to evaluate if similar gains could be realized when sound sources varied across both horizontal and vertical planes simultaneously. Results revealed interactions across spatial domains that partially hindered the recovery of spatial hearing abilities, although measurable gains in performance were nonetheless observed. Finally, utilizing a custom earmuff-style hearing protector, the last study investigated the cues underlying the discrimination of frontal and rear hemifield sound sources and changes that occur following the adaptation to degraded cues. Altogether, these works highlight the plasticity of and barriers to human sound localization with degraded spatial cues. These results directly inform the design of next-generation hearing devices that support both hearing protection and auditory spatial perception.