Analyzing Auditory Evoked Cortical Response to Noise-suppressed Speech in Cochlear Implant Users Using Mismatch Negativity

Speech perception in background noise remains a challenge in cochlear implant (CI) users, and noise-suppression processing (e.g., Wiener filtering) has been commonly utilized to improve speech perception for CI users. It is crucial to objectively examine the perception of the noise-suppressed speech in CI users. The purpose of this work was to investigate whether the mismatch negativity (MMN) response could objectively assess the quality of the noise-suppressed speech as perceived by CI users. A vowel /a/ stimulus was masked by a steady-state noise, creating two noisy stimuli at two signal-to-noise ratios (SNRs) of -5 and +5 dB. The two noisy stimuli were processed by Wiener filtering. Electroencephalogram data obtained from 7 CI users who participated in an auditory oddball paradigm was analyzed to extract the MMN. The two noise-suppressed stimuli served as the deviant stimuli and the clean vowel stimulus as the standard stimulus. Experimental results showed that the noise-suppressed stimuli at -5 dB SNR evoked a larger MMN amplitude than that at +5 dB SNR, accounting for the effect of SNR level on the auditory evoked cortical response to the noise-suppressed speech. The MMN may be potentially used as an objective biomarker to evaluate the perception of the noise-suppressed speech in CI users.