Impact of hearing protection devices on sound localization performance

Abstract

Hearing Protection Devices (HPDs) can protect the ear against loud potentially damaging sounds while allowing lower-level sounds such as speech to be perceived. However, the impact of these devices on the ability to localize sound sources is not well known. To address this question, we propose two different methods: one behavioral and one dealing with acoustical measurements. For the behavioral method, sound localization performance was measured with, and without, HPDs on 20 listeners. Five HPDs, including both passive (non-linear attenuation) and three active (talk-through) systems were evaluated. The results showed a significant increase in localization errors, especially front-back and up-down confusions relative to the “naked ear” test condition for all of the systems tested, especially for the talk-through headphone system. For the acoustic measurement method, Head-Related Transfer Functions (HRTFs) were measured on an artificial head both without, and with the HPDs in place. The effects of the HPDs on the spectral cues for the localization of different sound sources in the horizontal plane were analyzed. Alterations of the Interaural Spectral Difference (ISD) cues were identified, which could explain the observed increase in front-back confusions caused by the talk-through headphone protectors.

Effects of Active and Passive Hearing Protection Devices on Sound Source Localization, Speech Recognition, and Tone Detection

“…The study was also unique in its measurement of multiple auditory perceptual capacities across the same HPDs in the same group of subjects [ 7 ], and in its precise measurement of localization accuracy per se using an ecologically valid response paradigm [ 6 ]. Concordant with previous reports, HPD use significantly degraded sound localization [ 5 , 6 , 8 ] and signal detection [ 7 , 12 ]. Speech recognition was also somewhat degraded, although one HPD (the EB15) did not significantly change performance.…”

“…The Hybrid—the previously untested active device—gave the worst overall performance, while the Combat Arms and EB15 devices produced an intermediate number of errors. Toward a deeper understanding of the incidence of front-back confusions with the tested HPDs, we completed acoustic measurements using a test manikin fitted with the tested HPDs and attempted to relate patterns in acoustic distortions caused by HPDs to patterns in psychophysical localization data [ 8 ].…”

“…However, HPDs partially or fully occlude the external ear canal and/or concha, and can thus significantly distort SS cues [ 20 , 21 ]. Consequently, subjects tested in auditory spatial tasks during HPD use exhibit high rates of “front-back” and “up-down” errors [ 8 ]. Reduced ability to localize sound sources is detrimental to situational awareness, and may threaten survivability in high-risk situations [ 22 ].…”

“…The experiments described in this report were designed to measure the effect of four different HPDs (two active, two passive) on (1) sound source localization, (2) speech recognition, (3) and tone detection in a group of young, normal-hearing subjects. Psychophysical measurements were compared to measurements of head-related transfer functions made using a binaural test manikin with and without tested HPDs in place [ 8 ]. Collectively, data demonstrated minor decrements in tone detection and speech recognition ability during HPD use, but marked increases in sound localization errors that were strongly predicted by the degree of SS cue distortion produced by each of the four devices.…”

Avaliação do protetor auditivo em situação real de trabalho pelo método field Microphone-in-real-ear

“…An insertion-type HP of nonlinear attenuation normally includes a sound path with an acoustic impedance according to the velocity of the particle. This impedance is linked to its viscous resistance, which has a nonlinear component proportional to the velocity of the particle (25) .…”