Training sound localization in normal hearing listeners with and without a unilateral ear plug.

Surprisingly little is known about the ability of adult human listeners to learn to localize sounds in the free field. In this study, we presented broadband noise bursts at 24 equally spaced locations in a 360° horizontal plane in both normal-hearing conditions and when listeners were fitted with a unilateral earplug. Localization improvement was found over the initial four training sessions, prior to plug insertion which produced an immediate and profound impairment in localization, particularly on the side of the plug. Subsequent training with the plug in place over the next 5 days showed continually improving performance (learning) up to the 4th day. Following plug removal, localization immediately returned to pre-plug levels. These results showed that task-specific training can improve localization ability in normal-hearing conditions and that training also improves performance during a unilateral conductive hearing loss. It has been suggested that the process of learning is due to a gradual reweighting of the available cues to develop a new location map. The return to preplug learning performance suggests that the original location map is preserved despite the formation of a new map, and is in agreement with other reported findings.