The purpose of this study was to determine how well humans localize sound sources in the horizontal plane while wearing protective headgear with and without hearing protection. In a source identification task, a stimulus was presented from 1 of 20 loudspeakers arrayed in a semicircular arc, and participants stated which loudspeaker emitted the sound. Each participant was tested in 8 conditions involving various combinations of wearing a Kevlar army helmet and two types of earplugs. Testing was conducted at each of 2 orientations (frontal and lateral). In the frontal orientation, overall error was slightly greater in all protected conditions than in the bare-head control condition. In the lateral orientation, overall error score in the protected conditions was substantially and significantly greater than in the bare-head control conditions. Most errors in the lateral orientation were accounted for by front-back confusions, indicating that the protective devices disrupted high-frequency spectral cues that are the basis for discriminating front from back sound sources. The results have practical implications for the use of protective headgear and earplugs in industrial or military environments where localization of critical sounds is important.

Approved for public release; distribution is unlimited. AbstractThis report is a lexicon of terms developed by the Department of Defense Spatial Audio Display Working Group in an attempt to standardize terminology used by human factors researchers working in the area of auditory displays and human-machine communication. The lexicon has been primarily developed for the U.S. armed forces research groups, but it is hoped that it will be also useful for other Government academic, and industrial organizations. In addition to definitions specific to auditory displays, speech communication, and audio technology, the lexicon includes several terms unique to military operational environments and human factors engineering applications. Furthermore, human factors researchers appear to be increasingly interested in conducting integrated studies of auditory and visual perception in order to answer broad questions related to human situational awareness and performance. Therefore, the lexicon also includes some definitions related to visual perception, particularly in the areas of visual displays, virtual reality, and communication symbology. ACKNOWLEDGMENTSThe authors would like to thank Carolyn Bennett

The purpose of this study is to determine how well normal-hearing humans can localize sound sources while wearing protective headgear with and without hearing protection. Six subjects will participate in a source identification task to be conducted in an anechoic chamber. On each trial the stimulus (a 100-ms broadband source) will be presented from one of 20 loudspeakers arrayed in a semicircular arc, and the subject must state which loudspeaker emitted the sound. The arc spans 160° in the horizontal plane at ear level and is about 1.8 m distant from the subject. Each subject will be tested in eight conditions, involving various combinations of wearing protective headgear and three types of earplugs: the EAR plug and the Etymotic ER15 and ER25 ‘‘musician’s’’ earplugs. In addition, testing will be conducted at each of two orientations: frontal (center of the array at subject’s midline) and lateral (center of the array at 90° azimuth). Results are expected (a) to reveal whether the Etymotic earplugs (which are designed to attenuate equally across a broad frequency range) preserve localization accuracy, and (b) to quantify the interactive effects on localization performance of protective headgear and earplugs. [Work supported by NIDCD and NOHR.]

The purpose of this investigation was to examine the effects of presentation mode on speech intelligibility in adverse listening conditions as signal-to-noise ratio was systematically varied in anechoic and reverberant environments. Speech intelligibility scores were obtained from 21 normally hearing listeners using a nonsense syllable test. The syllables were recorded in three environments (mono anechoic, spatial anechoic and spatial reverberant) at three SNR (0, 5, and 9dB) using two simultaneous interfering sound sources. The findings indicate (a) percent correct performance was about 40% lower with the traditional diotic presentation compared to a virtual presentation; (b) performance in the virtual reverberant was about 5% lower than in the virtual anechoic environment.

The purpose of this investigation was to examine the effects of real and virtual adverse conditions on speech intelligibility. The experiment was designed to examine the effect of presentation method on speech intelligibility in conditions of noise and reverberation as signal-to-noise ratio was systematically varied. Additionally, this investigation evaluated the influence of talker gender on speech intelligibility in anechoic and reverberant environments as a function of signal-to-noise ratio and presentation method. Speech intelligibility scores were obtained from 21 normal hearing subjects using a nonsense syllable test. The syllables were recorded in three environments (diotic anechoic, virtual anechoic, and virtual reverberant) with three signal-to-noise ratios (0, 5, 9 dB) using two simultaneous masking sources. The findings indicate that (a) traditional diotic presentation of these stimuli degrades speech intelligibility compared to virtual presentation and may not accurately represent real-world performance; (b) the signal-to-noise ratios did not influence performance trends between presentation modes, as intelligibility improved with increasing SNR; (c) reverberation decreased intelligibility although the effects were not as dramatic as expected; and (d) using these stimuli, the female talker tokens were more easily identified than male talkers in a virtual presentation, but not generally for diotic presentation. [Work supported by NICDC and U.S. Army.]