Refractory effects of the N1 event-related potential in experienced cochlear implant patients

Abstract

Objective: To determine if cochlear implant (CI) patients exhibit a temporal processing deficit for auditory stimuli, by examining refractory effects of the N1 event-related potential (ERP) component. Design: CI patients and normally-hearing controls were tested in an auditory refractory period paradigm while ERP recordings were collected across the scalp. Participants were presented with brief 500-Hz tones that were separated by inter-stimulus intervals (ISIs) of 500, 1000, or 3000 ms. The amplitude of the N1 was examined as a function of ISI within each group. Study sample: Ten adult CI patients and 13 age-matched normally-hearing controls were tested. Patients had long-lasting severe or profound sensorineural hearing loss prior to implantation, and a minimum of two years experience with CI activation. Results: Unlike normally-hearing controls, CI users showed no refractory effect for tones at 500 ms ISIs compared to 1000 ms. However, similar to controls, recovery from refractoriness was observed in anterior locations at 3000 ms. Conclusion: The refractory period threshold, defined as the minimum ISI where different N1 amplitudes are elicited, is greater than 1000 ms in CI patients; at least double that of normally-hearing controls.

Key Words::

• Cochlear implant
• EEG
• hearing loss
• auditory evoked potential (AEP)
• auditory refractory period

Declaration of interest: This research was funded by the Nova Scotia Health Research Foundation. AJN was supported by the Canada Research Chairs program. CCS was supported by a CGS Scholarship from Canadian Institutes of Health Research.