Acoustic factors affecting interaural level differences for cochlear-implant users.

Bilateral cochlear-implant (BICI) listeners primarily use interaural level differences (ILDs) to localize sound in the horizontal plane. However, the ILD magnitude is altered at different frequencies and azimuths due to a combination of several acoustic phenomena such as the acoustical bright spot, acoustic axis, and microphone porting. This paper investigated the effects of BICI microphone placement on ILDs through an analysis of head-related transfer functions. At-the-canal BICI microphone placement provided both larger and more monotonic ILD-azimuth functions than behind-the-ear microphone placement. Results have implications for the fitting of clinical devices and their effect on sound localization in BICI users.