The Effect Of The AGC On Sound Localisation

Schleich P, Nopp P

Objectives: The main purpose of the dual-loop Automatic Gain Control (AGC) in the MED-EL COMBI 40+ cochlear implant (CI) system is compress the acoustic dynamic range into the electric dynamic range and to maintain relatively stable loudness across a wide range of sound pressure levels. However, the AGC also affects the effective size of the head shadow in bilateral cochlear implant users. Mismatched compression onsets lead to an artificial interaural level difference. This study aims at assessing the principal effect of mismatched compression onsets on sound localisation in bilateral CI users.

Study design: Sound localisation in the frontal horizontal plane is assessed with matched an mismatched AGCs. With matched AGCs the compression onset is the same at both sides. With mismatched AGCs the
compression onset is at 48 dB SPL on one side and at 65 dB SPL on the other side.

Results: Mismatched AGCs lead to a consistent localisation bias towards the side with the lower compression onset and a higher localisation error.

Conclusions: Matching the onsets of compression is essential for correct sound source localisation.

Contact Information

Mag. Peter Schleich
Research & Development
MED-EL Worldwide Headquarters
Fürstenweg 77A
6020 Innsbruck, Austria
Phone: +43-512-288889-422
Fax: +43-512-288889-490
Email: peter.schleich@medel.com