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

Abstract

Objectives: The 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.Methods: Ten 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). Results:Behavioral 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.Conclusion: Our 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.

The Acoustic Change Complex in Response to Frequency Changes and Its Correlation to Cochlear Implant Speech Outcomes

“…The ACC does not require the individual’s attention to the stimuli or behavioral response and thus is suitable for difficult-to-test patients. The ACC measures (e.g., the minimum sound change that can evoke an ACC, the ACC peak amplitudes and latencies) were found to be in agreement with the behavioral performance of auditory discrimination tasks ( Martin, 2007 ; Mathew et al, 2017 ; Han and Dimitrijevic, 2020 ). The ACC has shown to be reliable in normal hearing listeners, individuals with hearing loss, and CI users ( Tremblay et al, 2003 ; Friesen and Tremblay, 2006 ; Martin, 2007 ; Martinez et al, 2013 ; Mathew et al, 2017 ).…”

Electrophysiological assessment of temporal envelope processing in cochlear implant users

“…The ACC has been successfully used as an electrophysiological measure of gap detection 33 , frequency change detection 34 , and the eACC for electrode discrimination [35][36][37] in CI users. Furthermore, the eACC N1 amplitude shows a similar pattern as the temporal modulation transfer function of CI users 38 . It is, however, unclear if the eACC is able to reflect the TEM encoding ability of the stimulated neural ensembles of an individual CI user.…”

“…Nevertheless, Mathew et al 35,36 successfully used the eACC to assess electrode www.nature.com/scientificreports/ discrimination, and as long as the alteration made between two alternating stimuli cannot be attributed to confounding factors, this can be a clinically relevant measure which is little troubled by the stimulation artifacts. The electrophysiological measures used in the present study originate from regions in the auditory pathway beyond the periphery 17,38 and are assumed to reflect the processing cascade of all neural ensembles involved in TEM encoding of the ascending auditory pathway up to generator of the neural response. It is therefore difficult to derive from these measures where in the ascending auditory pathway TEM encoding is affected.…”

The Benefit of Cross-Modal Reorganization on Speech Perception in Pediatric Cochlear Implant Recipients Revealed Using Functional Near-Infrared Spectroscopy

“…It is known that CI listeners can make considerable use of AMs to assist with speech recognition (Shannon et al, 1995), as evidenced by some remarkable early studies that showed implant recipients could obtain a degree of speech understanding with only a single channel device (Tyler, 1988;Rosen et al, 1989;Rosen, 1992). This demonstrates that a large proportion of the information necessary for successful speech recognition is associated with the modulating envelope of speech signals (De Ruiter et al, 2015;Dimitrijevic et al, 2016;Han and Dimitrijevic, 2020). Therefore, it is plausible that poor speech performance amongst CI users could result from inadequate transmission of the AM signal from the CI to the brain.…”