Exploring Artifact Rejection for High-pulse Rate Electrically Evoked Auditory Steady State Responses in Cochlear Implants Users

The electrically evoked auditory steady state response (eASSR) is a potential objective measurement for cochlear implant (CI) fitting. Similar to other electroencephalography (EEG) measurements with CI users, artifacts caused by the pulsatile electric stimulation are phase locked to the stimulus and cannot be further reduced via an increasing number of repetitions. This is particularly problematic for high-pulse-rate eASSR, where the artifact temporally overlaps with a large part of the desired brain response. Here, an off-line CI artifact reduction technique, referred to as moving strobe averaging (MSA), is proposed and evaluated using highly-controlled EEG measurement data which deliberately do not contain a brain response: 1) simulated idealized data and 2) two dummy EEG recordings collected with either an electric resistor circuit to mimic scalp impedances (CI-in-a-box) or a saline solution filled tank (CI-in-atank) setup. The MSA algorithm supports identification of the artifact in the time domain and only requires that the artifact duration remains shorter than the inter-stimulus interval. In addition to being computationally efficient, MSA allows for removal of the stimulation artifact with minimal distortion of the desired neural response. Potential limitations of artifact rejection caused by the recording equipment itself are identified.