Seminars in Hearing Research

Date: Thursday, October 24, 2024

Location: Nelson Hall, Room 1215

Time: 12:00-1:00pm

Speaker:  Charlotte Garcia, Postdoctoral Researcher, University of Cambridge  

Title: Electrophysiological measures of auditory perception in cochlear implant users from the electrode-neuron interface to the cortex.

Abstract: Cochlear Implants (CIs) are arguably the most successful neuro-prosthetic device today and restore auditory perception to severe-to-profoundly deaf individuals by directly stimulating the auditory nerve. Many people do very well with their devices, but there is significant variability between users, both in their hearing pathologies and their ability to understand speech through their implants. While stimulation settings are adjusted in clinic to achieve appropriate volumes of sound perception for each cochlear-implant user, this is a subjective and time-consuming process that is infeasible for infants, and is not optimized to each individual patients’ unique pattern of hearing loss. To improve speech perception for those who struggle to communicate with their CIs, development of objective, electrophysiological measures of auditory perception can help to characterize the interaction between each individual patients’ implant and their brain. These measures could then be leveraged to optimize speech perception for individual patients. This seminar will focus on two projects whose aims are to characterize auditory perception of individual CI users using electrophysiological techniques. At the periphery, the Panoramic ECAP Method aims to characterize the interface between the electrodes of a CI and the auditory nerve they stimulate along the length of the cochlea. This is done using measurements of the population-level compound action potentials of auditory nerves in response to stimulation with a CI, and is recorded using the electrodes of the device itself. The method provides estimates of current spread and neural responsiveness and it’s variation along the length of an individual CI user’s cochlea, and has great potential for translation to clinic because no additional hardware is needed to run the test. However, this only characterizes the periphery of electrical hearing and cannot be representative of any higher-order auditory perception. Electroencephalography (EEG) can be used to measure auditory responses at the cortical level, but this can easily be masked by the electrical artefacts from CI stimulation of the auditory nerve. ALFIES (ALternating Frequency Interleaved Electrical Stimulation) is a method for extracting cortical neural responses from stimulation artefacts at stimulation rates representative of standard CI programming strategies. This is done by stimulating with two interleaved amplitude-modulated current-pulse trains, and relies on the assumption that while the EEG system is linear, there is smoothing in the brain that precedes its nonlinearities and results in a perceptible distortion product at a frequency where there is no electrical artefact. The recording system of the CI itself has also been investigated to determine whether the response can be captured without the need for EEG equipment. Both these techniques could be used to characterize auditory perception in CI users where it is not possible to measure behavioural responses (such as with infants). Development and translation of these sorts of personalized hearing healthcare techniques may improve speech perception for cochlear-implant users that would otherwise struggle to communicate with the auditory world around them.

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The working schedule is available here: https://purdue.edu/TPAN/hearing/shrp_schedule

The titles and abstracts of the talks will be added here: https://purdue.edu/TPAN/hearing/shrp_abstracts