Across-site patterns of electrically evoked compound action potential amplitude-growth functions in multichannel cochlear implant recipients and the effects of the interphase gap

The current study examined across-site patterns of suprathreshold ECAP measures in 10 bilaterally-implanted, adult cochlear implant users. Results showed that both peak amplitude and slope of the AGF varied significantly from electrode to electrode in ear-specific patterns across the subjects' electrode arrays. As expected, increasing the IPG on average increased the peak amplitude and slope. Across ears, there was a significant, negative correlation between the slope of the ECAP AGF and the duration of hearing loss. Across-site patterns of ECAP peak amplitude and AGF slopes were also compared with common ground impedance values and significant correlations were observed in some cases, depending on the subject and condition. The results of this study, coupled with previous studies in animals, suggest that it is feasible to measure the change in suprathreshold ECAP measures as the IPG increases on most electrodes. Further work is needed to investigate the relationship between these measures and cochlear implant outcomes, and determine how these measures might be used when programming a cochlear-implant processor.