Auditory localization in the horizontal plane with single and double hearing protection

Although most occupational noise problems can be adequately addressed with either earplugs or earmuffs, some extreme noise environments require listeners to wear both earplugs and earmuffs at the same time. However, little is known about the impact that double hearing protection has on sound localization. In this experiment, listeners wearing single and double hearing protection were asked to localize pink noise signals originating from 24 evenly spaced loudspeakers in the horizontal plane. In the single hearing protection conditions, localization accuracy was severely degraded with a short (250 ms) stimulus, but only modestly degraded with a continuous stimulus that allowed listeners to make exploratory head movements. In the double hearing protection conditions, localization accuracy was near chance level with the short stimulus and was only slightly better than chance with the continuous stimulus. A second experiment showed that listeners wearing double hearing protection were routinely unable to identify the lateral positions of stimuli originating from loudspeakers located at ±45° in azimuth. The results suggest that double hearing protection reduces the air-conducted signals in the ear canals to the point that bone and tissue conducted signals disrupt the interaural difference cues listeners normally use to localize sound. [Work supported by AFOSR.]