Phoneme recognition by cochlear implant users as a function of signal-to-noise ratio and nonlinear amplitude mapping

The present study measured phoneme recognition as a function of signal-to-noise levels when different nonlinear loudness mapping functions were implemented in three cochlear implant users using a 4-channel continuous interleaved sampler (CIS) strategy. Results show that phoneme recognition scores in quiet vary only slightly when different amplitude mappings from highly compressive to weakly compressive are applied. As the level of background noise is increased, recognition scores decrease more rapidly for the strongly compressive mapping than for the weakly compressive mapping. Results indicate that, although a strongly compressive mapping between acoustic and electric amplitude produces slightly better performance in quiet, a less compressive mapping may be beneficial for implant listeners in noisy listening conditions. (C) 1999 Acoustical Society of America.