Academic journal article Human Factors

Effects of Earplugs and Protective Headgear on Auditory Localization Ability in the Horizontal Plane

Academic journal article Human Factors

Effects of Earplugs and Protective Headgear on Auditory Localization Ability in the Horizontal Plane

Article excerpt


Localization represents a fundamental auditory skill that contributes to survival by indicating the presence and position of mates, prey, and enemies. Moreover, identification of sound source positions is an intimate part of modern-day orientation and surveillance of the environment. The ability to accurately localize and quickly identify the position of potential hazards is critical in combat and in many of today's work environments.

Military helmets are designed to protect soldiers from possible head injury during training and combat operations. Unfortunately, this protective headgear may also hinder the ability of a soldier to localize sounds. Although Randall and Holland (1972) reported that earlier helmet designs (the Hayes-Stewart and M-1 helmets) did not disrupt localization performance, Howse and Elfner (1982) reported that tanker helmets, when worn with various hearing-protective devices (HPDs), did result in an increase in localization errors compared with unprotected conditions. The differences in these results may have been attributable to the different shapes of the helmets studied. Specifically, the tanker helmet occluded the pinnae more than the earlier two helmet designs. The effects on localization of the newer Kevlar[R] helmet (Gentex Corp., Carbondale, PA; [ILLUSTRATION FOR FIGURE 1 OMITTED]), which is currently in use in the army, have not been investigated.

Additionally, it is well documented that HPDs (e.g., earmuffs and earplugs) designed to protect soldiers or employees from noise hazards and the possibility of noise-induced hearing loss result in significant localization difficulties (Abel & Hay, 1996; Atherly & Noble, 1970; Noble, Murray, & Waugh, 1990; Noble & Russell, 1972). However, it is not yet clear if the primary factor underlying decreased localization ability with HPDs is simply the overall attenuation provided by HPDs, or if the altered shape of the spectrum produced by HPDs also contributes to poorer performance. The former notion, called the attenuation hypothesis, received some support from studies indicating that as the attenuation of an HPD increased, so did the detrimental effect on localization performance (Mershon & Lin, 1987; Noble et al., 1990; Noble & Russell, 1972). However, given that these studies did not measure the frequency-specific attenuation characteristics of the various HPDs, it is not possible to know how disruption of spectral shape may have also contributed to the decreased localization performance.

Etymotic Research (Elk Grove Village, IL) has recently developed the ER25 "musician's" earplug, which is designed to attenuate evenly across the frequency spectrum (Killion, DeVilbiss, & Stewart, 1988; [ILLUSTRATION FOR FIGURE 2B OMITTED]). (Since this study was initially conceived, other manufacturers have developed "flat-response" HPDs, such as the 9000 earmuff and the "high-fi" earplug manufactured by Aearo Company, Indianapolis, IN.) By comparing performance with this earplug to performance obtained in a control condition in which no earplugs are worn but the source signal is attenuated by 25dB (the nominal specified attenuation for the ER25 earplug), it should be possible to determine whether such "flat" earplugs offer a significant advantage over conventional plugs in a localization task.

The purpose of the present study was to examine the effect of wearing the Kevlar helmet, one of two types of earplugs, or both the helmet and earplugs, on localization ability. Two sets of questions were addressed:

1. What are the effects, individually, of the Kevlar helmet, the E-A-R earplug (Aearo Co.), and the Etymotic ER25 musician's earplug on localization performance in the horizontal plane? If performance is degraded with the musician's earplug (compared with a bareheaded listening condition), can the degradation be accounted for simply by the attenuation provided?

2. …

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