Evaluating the N1-P2 Interpeak Latency of the eCAP and Its Intertrial Variability as Potential Indicators of Neural Synchrony in the Auditory Nerve of Cochlear Implant Users

OBJECTIVE: This study evaluated interpeak latency (IPL) and its intertrial variability (IPLVAR) of the electrically evoked compound action potential (eCAP) as potential alternatives to the phase-locking value (PLV) for quantifying auditory nerve (AN) synchrony in cochlear implant (CI) users. DESIGN: The IPL and IPLVAR were assessed in 28 postlingually deafened adults, 37 children with auditory neuropathy spectrum disorder (ANSD), 43 children with cochlear nerve deficiency, and 38 children with typical sensorineural hearing loss. All participant groups include both male and female participants. Their associations with temporal resolution and speech perception outcomes were evaluated in children with ANSD and/or adult CI users. Frequency analysis was conducted to understand the impacts of eCAP recording noise on the IPL, IPLVAR, and PLV. Simulations of intertrial jitter in the eCAP were performed to quantify how the IPL, IPLVAR, and PLV metrics varied with increased temporal jitter and its interaction with recording noise level and sampling rate. RESULTS: eCAP traces recorded in all patient groups showed a multipoint peak issue affecting the accuracy of IPL and IPLVAR assessments. Temporal resolution and speech perception outcomes were significantly correlated with IPLVAR but not with IPL metrics. The PLV was impacted less by recording noise than either the IPL or the IPLVAR. Simulation results revealed that the IPL was less sensitive to the amount of intertrial jitter in the eCAP than were the IPLVAR and the PLV. CONCLUSIONS: The IPL is not a reliable indicator of AN synchrony. The IPLVAR is indicative of neural synchrony in the AN; however, it is more strongly affected by high levels of eCAP recording noise than the PLV. The PLV is therefore the preferred measure for quantifying neural synchrony in the AN in CI users.