Acoustic Change Responses to Amplitude Modulation in Cochlear Implant Users: Relationships to Speech Perception.

Ji-Hye Han,Andrew Dimitrijevic

doi:10.3389/fnins.2020.00124

Abstract

ObjectivesThe ability to understand speech is highly variable in people with cochlear implants (CIs) and to date, there are no objective measures that identify the root of this discrepancy. However, behavioral measures of temporal processing such as the temporal modulation transfer function (TMTF) has previously found to be related to vowel and consonant identification in CI users. The acoustic change complex (ACC) is a cortical auditory-evoked potential response that can be elicited by a “change” in an ongoing stimulus. In this study, the ACC elicited by amplitude modulation (AM) change was related to measures of speech perception as well as the amplitude detection threshold in CI users.MethodsTen CI users (mean age: 50 years old) participated in this study. All subjects participated in behavioral tests that included both speech and amplitude modulation detection to obtain a TMTF. CI users were categorized as “good” (n = 6) or “poor” (n = 4) based on their speech-in noise score (<50%). 64-channel electroencephalographic recordings were conducted while CI users passively listened to AM change sounds that were presented in a free field setting. The AM change stimulus was white noise with four different AM rates (4, 40, 100, and 300 Hz).ResultsBehavioral results show that AM detection thresholds in CI users were higher compared to the normal-hearing (NH) group for all AM rates. The electrophysiological data suggest that N1 responses were significantly decreased in amplitude and their latencies were increased in CI users compared to NH controls. In addition, the N1 latencies for the poor CI performers were delayed compared to the good CI performers. The N1 latency for 40 Hz AM was correlated with various speech perception measures.ConclusionOur data suggest that the ACC to AM change provides an objective index of speech perception abilities that can be used to explain some of the variation in speech perception observed among CI users.

Highlights

Cochlear implants (CIs) provide electrical stimulation to the auditory nerve that can, in turn, be interpreted by the brain as sound including speech
AM Change: CI vs. NH Grand mean data are shown in Figure 2A illustrating the cortical potentials at FC electrodes for the AM changes at 4, 40, 100, and 300 Hz with a schematic of the stimulus overlaid
The N1 responses to AM change were robust in some cases, not all CI participants had a measurable response

Summary

Introduction

Cochlear implants (CIs) provide electrical stimulation to the auditory nerve that can, in turn, be interpreted by the brain as sound including speech. Used objective measures such as the stapedius reflex, electrically evoked compound action potentials, and electrically evoked auditory brainstem responses have shown poor correlation with speech perception (Abbas and Brown, 1991; Hirschfelder et al, 2012; Lundin et al, 2015). Unlike these peripheral measures, cortical activity measured at the sensory and source levels has shown some reliable relationships with behavioral performance in adult CI users in research settings (Han et al, 2016; Gransier et al, 2019)

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