Evaluation of an Artifact Reduction Strategy for Electrically Evoked Auditory Steady-State Responses: Simulations and Measurements

Background: Electrically evoked steady-state response (EASSR) recording is a measure of neuronal response strength after continuous electrical stimulation of the auditory system. To suppress the large electrical artifact generated by intracochlear electrical stimulation, a sophisticated artifact reduction processing strategy (“Hofmann procedure”) has been proposed (Hofmann and Wouters, 2010). EASSR recordings with artifact reduction procedures were reported only in cochlear implant (CI) users implanted with Cochlear devices (Macquarie, Australia).

Methods: Here, we demonstrate the application of the Hofmann procedure in CI users implanted with MED-EL (Innsbruck, Austria) devices. To demonstrate potential limitations of the procedure, we calculated discrete time Fourier transformations of various pulse patterns which may be used for EASSR.

Results: EASSR recordings were obtained in three subjects and processed with the Hofmann procedure. Neural response amplitude growth functions and phase for modulated and unmodulated pulse trains at various stimulation rates could be assessed. Simulations of three different interpolation methods aimed to suppress the electrical artifact show that the interpolation of a sinusoidal signal in a temporal window between 0 and 1 ms has demonstrated negligible impact on the spectral amplitude of the signal with a superior performance of a spline interpolation.

Conclusions: The Hofmann procedure was validated for recording EASSRs with CIs from the manufacturer MED-EL.