Effects on sound localization of configuration and type of hearing impairment.

Localization ability of 87 bilaterally hearing-impaired listeners was tested in the horizontal and vertical planes, frontally and laterally. In those with sensorineural hearing loss, it was found that deficits in localization accuracy in different regions of auditory space could be related to different configurations of hearing loss. For example, there were associations between vertical plane discrimination and high-frequency sensitivity; and front-rear discrimination and mid-to-high-frequency sensitivity. These results agree with theoretical expectations, while the outcome overall contrasts with previous reports that localization performance is unrelated to audiometric configuration. A comparison of 13 listeners with conductive/mixed types of impairment with a sensorineural-loss group, matched for degree of loss, showed that a conductive component adds significantly to localization disturbance, particularly in the horizontal plane. The probable reason is a disturbance of low-frequency interaural time cues, and this occurs because a higher proportion of low-frequency sound is likely to be transmitted via bone conduction relative to air conduction. Correlations between hearing loss and localization are only moderate, suggesting that aspects of hearing impairment, in addition to simple attenuation, may also reduce auditory localization performance.