Evaluation of Speech Recognition of Cochlear Implant Recipients Using a Personal Digital Adaptive Radio Frequency System

Abstract

Previous research supports the use of frequency modulation (FM) systems for improving speech recognition in noise of individuals with cochlear implants (CIs). However, at this time, there is no published research on the potential speech recognition benefit of new digital adaptive wireless radio transmission systems. The goal of this study was to compare speech recognition in quiet and in noise of CI recipients while using traditional, fixed-gain analog FM systems, adaptive analog FM systems, and adaptive digital wireless radio frequency transmission systems. A three-way repeated-measures design was used to examine performance differences among devices, among speech recognition conditions in quiet and in increasing levels of background noise, and between users of Advanced Bionics and Cochlear CIs. Seventeen users of Advanced Bionics Harmony CI sound processors and 20 users of Cochlear Nucleus 5 sound processors were included in the study. Participants were tested in a total of 32 speech-recognition-in noise-test conditions, which included one no-FM and three device conditions (fixed-gain FM, adaptive FM, and adaptive digital) at the following signal levels: 64 dBA speech (at the location of the participant) in quiet and 64 dBA speech with competing noise at 50, 55, 60, 65, 70, 75, and 80 dBA noise levels. No significant differences were detected between the users of Advanced Bionics and Cochlear CIs. All of the radio frequency system conditions (i.e., fixed-gain FM, adaptive FM, and adaptive digital) outperformed the no-FM conditions in test situations with competing noise. Specifically, in conditions with 70, 75, and 80 dBA of competing noise, the adaptive digital system provided better performance than the fixed-gain and adaptive FM systems. The adaptive FM system did provide better performance than the fixed-gain FM system at 70 and 75 dBA of competing noise. At the lower noise levels of 50, 55, 60, and 65 dBA, no significant differences were detected across the three systems, and no significant differences were found across the quiet conditions. In all conditions, performance became poorer as the competing noise level increased. In high levels of noise, the adaptive digital system provides superior performance when compared to adaptive analog FM and fixed-gain FM systems.