Cochlear implant artifact attenuation in late auditory evoked potentials: A single channel approach

Abstract

a b s t r a c tRecent evidence suggests that late auditory evoked potentials (LAEP) provide a useful objective metric of performance in cochlear implant (CI) subjects. However, the CI produces a large electrical artifact that contaminates LAEP recordings and confounds their interpretation. Independent component analysis (ICA) has been used in combination with multi-channel recordings to effectively remove the artifact. The applicability of the ICA approach is limited when only single channel data are needed or available, as is often the case in both clinical and research settings. Here we developed a single-channel, high sample rate (125 kHz), and high bandwidth (0e100 kHz) acquisition system to reduce the CI stimulation artifact. We identified two different artifacts in the recording: 1) a high frequency artifact reflecting the stimulation pulse rate, and 2) a direct current (DC, or pedestal) artifact that showed a non-linear time varying relationship to pulse amplitude. This relationship was well described by a bivariate polynomial. The high frequency artifact was completely attenuated by a 35 Hz low-pass filter for all subjects (n ¼ 22). The DC artifact could be caused by an impedance mismatch. For 27% of subjects tested, no DC artifact was observed when electrode impedances were balanced to within 1 kU. For the remaining 73% of subjects, the pulse amplitude was used to estimate and then attenuate the DC artifact. Where measurements of pulse amplitude were not available (as with standard low sample rate systems), the DC artifact could be estimated from the stimulus envelope. The present artifact removal approach allows accurate measurement of LAEPs from CI subjects from single channel recordings, increasing their feasibility and utility as an accessible objective measure of CI function.

Peripheral and Central Contributions to Cortical Responses in Cochlear Implant Users

“…By balancing impedances across the recording electrodes, we reduced direct-current (DC; or, “pedestal”) artifact. The amplifier low-pass filter cut-off frequency reduced the high-frequency artifact (McLaughlin et al 2013). For each pair of electrodes, 100 sweeps were collected when using electrode 12 to elicit the onset response and 100 sweeps when using electrode 12 to elicit the ACC.…”

Cortical auditory evoked potentials as an objective measure of behavioral thresholds in cochlear implant users

“…CAEPs can be difficult to record clinically, due to the need for placement of scalp electrodes, a relatively long recording time due to the number of repetitions needed and duration of the response, and due to the large effect of attention/sleep state, which is particularly important when testing children. Recent advances may make clinical recordings of CAEPs for CI users far simpler due to the possibility of recording from extracochlear electrodes (McLaughlin et al, 2013) and improved signal processing techniques such as dynamical embedding that may allow responses to be extracted from noise and artefacts using a small number of trials and channels (Fisher et al, 2007). CAEPs have been recorded in CI users as a measure of cortical maturation (Sharma et al, 2002(Sharma et al, , 2005(Sharma et al, , 2007 and as on objective measure of auditory function (Beynon and Snik, 2004;Beynon et al, 2005Beynon et al, , 2002Kelly et al, 2005).…”

Cortical Activation Patterns Correlate with Speech Understanding After Cochlear Implantation

“…Key EEG studies have argued that late auditory evoked potentials provide a useful objective metric of performance in participants hearing through a cochlear implant (Firszt et al 2002; Zhang et al 2010; Zhang et al 2011). However EEG does have a disadvantage in that CIs produces electrical noise that can interfere with recordings when long duration speech stimuli are used, although artifact removal techniques can be used to minimize this issue (Viola et al 2012; Mc Laughlin et al 2013; Miller and Zhang 2014). …”