Academic journal article Human Factors

Effects of Hearing Protectors on Auditory Localization in Azimuth and Elevation

Academic journal article Human Factors

Effects of Hearing Protectors on Auditory Localization in Azimuth and Elevation

Article excerpt

An experiment was conducted to determine the effects of two types of hearing protectors on auditory localization performance. Six listeners localized a 750-ms broadband noise from loudspeakers ranging in azimuth from -180[degrees] to + 180[degrees] and in elevation from -75[degrees] to +90[degrees]. Independent variables included the type of hearing protector and the elevation of the source. Dependent measures included azimuth error, elevation error, and the percentage of trials resulting in a front-back confusion. Performance on each of the dependent measures was found to be mediated by one or more of the independent variables. Actual or potential applications include the generation of improved design guidelines for hearing protectors and workplace alarms.


A great deal of attention has been given over the years to the manner in which the wearing of hearing protectors affects auditory localization in the horizontal plane (Abel & Armstrong, 1993; Atherley & Noble, 1970; Noble & Russell, 1972; Vause & Grantham, 1999). The results of these investigations have generally indicated that for the stimuli employed, horizontal localization is severely disrupted and that the cause of much of the disruption is an increase in the number of front-back confusions (i.e., errors resulting from correctly localizing a source in the right/left dimension while mislocalizing it in the front/ back dimension; Vause & Grantham, 1999). Such confusions arise from the fact that one of the dominant cues for sound localization, the interaural difference in the arrival time of the sound at the eardrum, does not uniquely specify a location in space, only the right/left component (Oldfield & Parker, 1984b). One of the reasons that these confusions do not occur often in everyday life is the tran sformation of the incident sound wave by its interaction with the pinnae, which produces different spectral patterns for sources in the front and rear hemispheres (Musicant & Butler, 1984). Thus it is reasonable to expect that the introduction of hearing protectors, which disturb the spectrum of the incident wave, would result in a degradation in front-back discrimination.

In addition, it is equally reasonable to expect that localization of sound sources outside the horizontal plane would be disrupted when hearing protectors are worn, given that spectral information is known to be the dominant cue for localization in elevation (Roffler & Butler, 1968). In spite of this, few researchers (Noble, 1981) have investigated the effects of hearing protectors on the localization of sounds with nonzero elevation. The purpose of the present investigation is to determine the effects of hearing protectors on localization acuity in azimuth and elevation for sources distributed throughout auditory space.



All testing was conducted in the Air Force Research Laboratory's Auditory Localization Facility (ALF) at Wright-Patterson Air Force Base, Ohio. In this facility, listeners sat in a specially designed chair equipped with chin rest and response apparatus and situated at the center of a geodesic sphere of diameter 4.6 m housed in a cubic anechoic chamber whose sides measured 6.7 m. The aluminum struts of the sphere were covered with 2.5 cm of foam to minimize acoustic reflections. Located at each of the sphere's 272 vertices, spaced approximately 15[degrees] apart, was a Bose 4.5-in. Helical Voice Coil full-range loudspeaker (Model 118038; Bose Corp., Framingham, Massachusetts) facing the center of the sphere. This enabled the presentation of stimuli from locations ranging from --180[degrees] to + 180[degrees] in azimuth and -70[degrees] to +90[degrees] in elevation.

Localization responses were collected using the God's Eye Localization Pointing (GELP) technique developed by Gilkey and his colleagues (Gilkey, Good, Ericson, Brinkman, & Stewart, 1995). …

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