Effects of long-term bilateral and unilateral fitting of different hearing aid types on the ability to locate sounds.

Aided localization ability of 87 hearing-impaired listeners was tested for horizontal and vertical sound sources, at two signal levels, and for two orientations to the loudspeaker array (facing, sideways). Some listeners wore behind-the-ear (BTE) aids, others in-the-ear (ITE) aids. Some were bilaterally fitted, others unilaterally fitted. Listeners were tested only with types of aids and fittings that they were accustomed to wearing. The results strongly supported bilateral fitting for moderately and severely hearing-impaired listeners. However, for mildly impaired listeners, those fitted unilaterally performed as well, on average, as those fitted bilaterally. This suggests a need to consider individual listening requirements and also to provide such listeners with experience in unilaterally-aided listening before assessing the possible advantages of bilateral fitting. When hearing level was controlled, there was no overall difference in the performance of ITE and BTE aid wearers. This discrepancy with other research may be explained by measures (removal of intensity cues, permitting of head movement) designed to make the test situation more representative of real-life listening.