Methods to Eliminate Stimulus Transduction Artifact From Insert Earphones During Electroencephalography

In Brief Objective: To reduce stimulus transduction artifacts in EEG while using insert earphones. Design: Reference Equivalent Threshold SPLs were assessed for Etymotic ER-4B earphones in 15 volunteers. Auditory brainstem responses (ABRs) and middle latency responses (MLRs)—as well as long-duration complex ABRs—to click and /dα/ speech stimuli were recorded in a single-case design. Results: Transduction artifacts occurred in raw EEG responses, but they were eliminated by shielding, counter-phasing (averaging across stimuli 180° out of phase), or rereferencing. Conclusions: Clinical grade ABRs, MLRs, and cABRs can be recorded with a standard digital EEG system and high-fidelity insert earphones, provided one or more techniques are used to remove the stimulus transduction artifact. This technical note documents three approaches to the problem of stimulus transduction artifact during EEG measurement. We use insert earphones (Etymotic ER-4B) for reproduction of high-frequency, high-fidelity acoustical information and a nonspecialized digital EEG acquisition system. Such standard EEG equipment has considerable potential for revealing how multiple levels of auditory processing reflect peripheral damage and lead to behavioral impairments. In this setting, the stimulus transduction artifact can contaminate scalp-recorded electrical responses to click stimuli, thus compromising the fidelity of clinically relevant auditory brainstem responses. Furthermore, with longer complex stimuli such as speech, this artifact can temporally overlap long epochs of the EEG responses, thus confounding their interpretation. Three methods are shown to eliminate the artifact (counter-phasing, referencing, and shielding).