Comparison of dual-time-constant and fast-acting automatic gain control (AGC) systems in cochlear implants.
Cochlear implants usually employ an automatic gain control (AGC) system as a first stage of processing. AGC1 was a fast-acting (syllabic) compressor. AGC2 was a dual-time-constant system; it usually performed as a slow-acting compressor, but incorporated an additional fast-acting system to provide protection from sudden increases in sound level. Six experienced cochlear-implant users were tested in a counterbalanced order, receiving one-month of experience with a given AGC type before switching to the other type. Performance was evaluated shortly after provision of a given AGC type and after one-month of experience with that AGC type. Questionnaires, mainly relating to listening in quiet situations, did not reveal significant differences between the two AGC types. However, fixed-level and roving-level tests of sentence identification in noise both revealed significantly better performance for AGC2. It is suggested that the poorer performance for AGC1 occurred because AGC1 introduced cross-modulation between the target speech and background noise, which made perceptual separation of the target and background more difficult.
Department of Experimental Psychology, University of Cambridge, Downing Street, Cambridge, UK. patrickb@abionics.fr
Patrick J
PJ
Boyle
Andreas
A
Büchner
Michael A
MA
Stone
Thomas
T
Lenarz
Brian C J
BC
Moore
D000161:Acoustic Stimulation; D000328:Adult; D000368:Aged; D001307:Auditory Perception; D003054:Cochlear Implants; D003638:Deafness / Q000523:psychology / Q000628:therapy; D006801:Humans; D008875:Middle Aged; D009146:Music; D010470:Perceptual Masking; D012984:Software; D013060:Speech; D013067:Speech Perception; D011795:Surveys and Questionnaires