Aided cortical auditory evoked measures with cochlear implantees: the challenge of stimulus artefacts

Abstract

Purpose: Cortical auditory evoked potential (CAEP) procedures are a useful way of estimating behavioural thresholds without active participant cooperation. They are becoming more common in hearing aid fitting, especially for those who cannot give reliable responses during evaluation. Speech stimuli are used in CAEP assessment to better understand listener performance when listening to speech. A commercial system, HEARLab (Frye Electronics, Tigard OR), detects and automatically analyses aided CAEPs elicited by speech stimuli. Aided CAEPs are also helpful in cochlear implant evaluation. However, there are few studies in this area, primarily due to electrical artefacts elicited by such devices. This study determined average CAEP waveform latency for CI users, and compared aided HEARLab cortical assessment (ACA) outcomes with behavioural speech detection results, using modified recording electrodes designed to reduce artefacts.

Method: Custom CAEP electrodes were used to reduce recording artefacts, and test outcomes compared with those obtained with standard electrodes. Recordings from participants using two types of cochlear implant device (Cochlear and Advanced Bionics) were also compared. Twenty adult cochlear implantees were assessed using ACA with both types of electrodes, and behavioural free field speech detection was also conducted.

Results: Average P1 latencies for the cochlear implant users were within the normative range of the general, non-implant population. The percentage of matches for positive results between ACA and behavioural speech detection test results was low, and the number of CAEPs recorded without artefacts was also low for both types of electrodes. More CAEPs could be recorded without artefacts with Cochlear devices regardless of the type of electrodes used. However, the artefact amplitudes recorded with Cochlear devices were greater than those produced by Advanced Bionics devices.

Conclusion: Custom electrodes were not effective in reducing the prevalence of CI-related artefacts, and the artefact amplitude recorded was slightly greater than for the original electrodes. Alternative methods should be trialled to reduce the effects of electrical artefacts on CAEP recordings with cochlear implant users.