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Translational Research II - The Killion Lecture

Auditory Situation Awareness: The Conundrum When Your Life Depends Upon Your Hearing and Your Hearing Depends on Your Hearing Protector
John G. Casali, PhD, CPE
Grado Professor and Director, Auditory Systems Lab, Virginia Tech University and Chief Technology Officer, Hearing, Ergonomics & Acoustics Resources (HEAR), LLC, Blacksburg, VA

Prevention of noise-induced hearing loss via hearing protection devices (HPDs), with concomitant preservation of one's auditory situation awareness (ASA) and vigilance to the surrounding acoustic environment, is critical.  Examples include construction workers who wear electronic earmuffs but must hear backup alarms, trail runners who wear earphones but need to hear bicycles that overtake from behind, emergency vehicle drivers who need hearing protection from the siren but must hear car horns, and military personnel who wear gunfire noise-protective headsets but must hear enemy threat signals and speech.  The human auditory sense provides key sensory-perceptual inputs for establishing situation awareness, due to the fact that it is always “on” and primed for response, is “omni-directional” and thus reactive to sounds coming from all directions, renders an “acoustic startle response” which provides quick arousal to dangers, and has a relatively low threshold of sensitivity even during sleep.  Unfortunately, when the ears are occluded with HPDs or earphones of various types, these auditory capabilities can be compromised. This presentation will provide a brief introduction into recent technologies in HPDs and earphone design, which rely on either passive (i.e., dynamically nonlinear acoustic "valves") or active (i.e., battery-electronic sound transmission) technologies, that are intended to provide "pass-through" hearing capability.  In addition, human subject research results from several in-field and in-lab ASA experiments will be covered.  Resultant data demonstrate that somedevices, including many augmented HPDs and military-fielded Tactical-Communications-and-Protective-Systems (TCAPS), in fact do not provide natural hearing or "transparency" but instead render an imprint on the incoming signals, and thus can impose deleterious effects on one’s situation awareness.  Experimental stimuli have included vehicular warning alarms and a variety of sound signatures of broadband, low-frequency, and high-frequency content. Metrics of ASA performance have included: hearing threshold at detection, accuracy and response time in recognizing/identifying and localizing signals, and intelligibility of communications. Based on these experiments, an objective, repeatable test battery was developed for evaluating ear-occluding device impacts on:  Detection, Recognition/Identification, Localization (azimuth and frontal elevation), and COMmunication, known as DRILCOM.  Example results, in particular with ubiquitous reverse alarms required by OSHA on industrial-construction vehicles as well as various threat signatures such as gunshots, are covered.  Also, the interactive effects of HPD design with the low-frequency interaural time difference (ITD) cues and high-frequency interaural level difference (ILD) cues that are critical to localization are covered. In addition to testing results, research on auditory training will be covered, particularly in regard to the ability of both the natural and occluded ear to be trained to achieve better localization performance.  Using a Portable Auditory Localization Acclimation and Training System (PALAT) developed and validated at Virginia Tech, which provides an array of directional loudspeakers and a dissonant tonal complex that is highly localizable, human factors experiments have demonstrated that spatial localization accuracy with the open ear can be improved with training by up to about 30% over baseline, and when wearing certain HPDs, improvements can also be obtained with training.  However, other HPDs and TCAPS have been found to be insensitive to training effects and induce localization and other errors, giving rise to questions about whether they should be deployed when the user needs to maintain ASA. The presentation postulates the need for ASA testing of HPDs and TCAPS, in similar fashion to Noise Reduction Rating (NRR) and other forms of pure attenuation testing.   Furthermore, the negative implications for noise-induced hearing loss when users’ perceive that HPDs impede their hearing of important signals and communications, and remove their protectors, are discussed.

NOTE:  This work received the "Safe in Sound Award for Innovation in Hearing Conservation," awarded by the United States National Institute for Occupational Safety and Health (NIOSH) in February, 2016.  See:  http://www.safeinsound.us/winners.html

Dr. Casali is the Grado Professor of Industrial & Systems Engineering at Virginia Tech (VT), and a Board-Certified Professional Ergonomist (CPE).  He founded the Auditory Systems Laboratory at VT in 1983.  He also is founder and CTO of HEAR, LLC, a product design and litigation support firm. He is a Fellow of the Institute of Industrial Engineers and the Human Factors & Ergonomics Society, the latter of which presented him with the Lauer Award in 2017 for advancements in worker and consumer safety.  He received the NIOSH-NHCA Safe-in-Sound Award for Innovation in Hearing Conservation in 2016, and the NHCA’s Outstanding Hearing Conservationist Award in 2009. His externally-sponsored contract research and foundation funding at VT has totaled over $15 million, he has 7 patents and over 200 publications, and he has advised 25 Ph.D. and 31 Master’s students to graduation.  Two of his auditory situation awareness training systems have been installed at U.S. military bases.  (Dr. Casali, with initiative and assistance from Dr. Mead Killion, conducted one of the earliest in-field experiments on auditory localization accuracy and response time to gunshots, as impacted by hearing protection devices versus the open ear, with implications for Auditory Situation Awareness.)