ELECTRODE DISCRIMINATION AND SPEECH RECOGNITION IN POSTLINGUALLY DEAFENED ADULT COCHLEAR IMPLANT SUBJECTS

This study investigated the relationship between electrode discriminat ion and speech recognition in 11 postlingually deafened adult cochlear implant subjects who were implanted with the Nucleus/ Cochlear Corpor ation multichannel device. The discriminability of each electrode incl uded in a subject's clinical map was measured using adaptive and fixed -level discrimination tasks. Considerable variability in electrode dis criminability was observed across subjects. Two subjects could discrim inate all electrodes, and discrimination performance by the remaining nine subjects varied from near perfect to very poor. Tn these nine sub jects, the results obtained from the discrimination tasks were used to create a map that contained only discriminable electrodes, and subjec ts' performance on speech recognition tasks using this experimental ma p was measured. Four different speech recognition tests were administe red: a nine-choice closed-set medial vowel recognition task, a 14-choi ce closed-set medial consonant recognition task, the NU6 Monosyllabic Words Test [T. W. Tillman and T. Carhart, Tech. Rep. No. SAM-TR-66-55, USAF School of Aerospace Medicine, Brooks Air Force Base, Texas (1966 )] scored for both words and phonemes correct, and the Central Institu te for the Deaf (CID) Everyday Sentences test [H. Davis and S. R. Silv erman, Hearing and Deafness (Holt, Rinehart, and Winston, New York, 19 78)]. Seven of the nine subjects tested with the experimental map show ed significant improvement on at least one speech recognition measure, even though the experimental map contained fewer electrodes than the original map. Three subjects' scores improved significantly on the CID Everyday Sentences test, three subjects' scores improved significantl y on the NU6 Monosyllabic Words test, and five subjects' scores improv ed significantly on the NU6 Monosyllabic Words test scored for phoneme s correct. None of the subjects' scores improved significantly on eith er the vowel or consonant tests. No significant correlation was observ ed between electrode discrimination ability and speech recognition sco res or between electrode discrimination ability and improvement in spe ech recognition scores when programmed with the experimental map. The results of this study suggest that electrode discrimination tasks may be used to improve speech recognition of some cochlear implant subject s, and that each electrode site does not necessarily provide perceptua lly distinct information. (C) 1997 Acoustical Society of America. [S00 01-4966(97)05212-0].