A preliminary study to identify a neurophysiological correlate of electroacoustic pitch matching in cochlear implant users

One challenge facing postlingually-deafened cochlear implant (CI) users is the frequency mismatch between the incoming acoustic signal and the characteristic frequency of the electrically stimulated neurons. Current CI is an open-loop system and it requires extensive fine-tuning to help users to adapt to this mismatch over time. Electric-acoustic pitch matching in unilateral cochlear implant (CI) participants who has residual hearing in the non-implanted ear had been shown to serve as a useful metric to monitor adaptation process. The goal of this study was to identify a potential neurophysiological correlate to this electroacoustic pitch matching for a possible metric to track the adaptation process of CI users over time and a possible feedback for a closed-loop CI system design. This study utilized a method of presenting electrical and acoustic stimuli that were continuously alternating across ears. The stimuli were either matched or mismatched in pitch. Auditory Evoked Potentials (AEP) were recorded from 10 CI users and 10 normal hearing (NH) participants. For NH participants, an acoustic tone at a fixed frequency was presented in place of electrical stimulation. Results with CI participants indicated that N1 latency decreases when the acoustic frequency of the tone presented in the non-implanted ear increases. More importantly, there was an additional shortening of N1 latency in the pitch matched condition. These two patterns were repeated with NH participants. These results indicate the potential utility of N1 latency as an index of pitch matching in both normal hearing listeners and cochlear implant user.