Sound Localisation With Fixed And Randomised Levels

Nopp, P, Schleich, P, D'Haese, P

Binaural hearing allows one to localize sound sources in space. Consequently, unilateral implant users report problems in localizing sounds and in positioning themselves in the 3-D world. Bilateral cochlear implantation is an attempt to restore binaural hearing. The purpose of this study is to assess the ability to localize sounds in bilateral cochlear implant (CI) users and to quantify the benefit in comparison to unilateral CI use.

Sound localisation in the frontal horizontal plane was tested in 20 subjects in a 9-loudspeaker arrangement under fixed (70 dB SPL) and roving (60/70/80 dB SPL) level conditions using CCITT noise. Tests were performed with using both CIs and either CI alone. All subjects were bilaterally implanted during adolescence or later. All subjects who were bilaterally deafened after five to six years of age (18 subjects) showed a statistically significant improvement in sound localization when using both implants. The mean azimuth deviation is 16.6° when using both implants, which is on an average 37.1° smaller than when using one implant only. Statistical analysis showed that in this group, performance measures were not correlated with subject details such as age at onset of deafness, or duration of unilateral implant use. In contrast, those subjects who were bilaterally deafened before six years of age (2 subjects) did not show a benefit in sound
localization from bilateral implants.
Bilateral cochlear implants offer a substantial benefit in sound localization to late-deafened, lateimplanted subjects. Early-deafened subjects implanted at a later age do not appear to benefit in sound localization from bilateral cochlear implants. This implies a high importance for early implantation to allow acquisition of spatial hearing.

Contact Information

Dr. Peter Nopp
Research & Development
MED-EL Worldwide Headquarters
Fürstenweg 77 A
6020 Innsbruck
Austria
Phone: +43-512-288889-410
Fax: +43-512-288889-490
E-mail: peter.nopp@medel.com