Simulating Speech Perception in Bilateral Cochlear Implant Users with Asymmetric Input

Abstract

Understanding speech in noise is difficult for cochlear-implant (CI) users. One potential reason for this difficulty is asymmetrical hearing between the two ears; that is, when one ear can process sound more effectively and clearly than the other ear. Such asymmetry may impair some CI users’ ability to fuse speech signals from both ears into a single stream. One way to test this is with an alternating speech paradigm, which is an experimental simplification of speech moving from talker to talker in a rapid conversation between a group of people. Previous studies have shown CI users perform 40% worse on alternating speech listening than normal-hearing individuals. The present study aims to examine if reduced alternating speech perception is the result of asymmetrical hearing, which could cause a listener to only use their better ear when listening to alternating speech, and to miss out on much of the signal that is present in the poorer ear. Six young normal-hearing participants were tested using a CI simulation with varying levels of signal degradation to simulate both asymmetrical and symmetrical hearing. The hypothesis was that participants will show selective attention to the ear with the clearer, less degraded signal in asymmetrical hearing conditions, and will overall perform worse in this condition compared to the symmetrical hearing condition. The results comparing the “better ear” and the asymmetric condition suggest that there is no evidence of selective attention; therefore we can reject the hypothesis. Future directions include increasing asymmetry across ears by simulating more drastic degradation in the “poorer ear”. Speech perception in noise is one of the most common issues CI users face, and quantifying the contributions of asymmetrical hearing to this problem is important for resolving this issue.