Comparing patient-specific variations in intra-cochlea neural health estimated using psychophysical thresholds and panoramic electrically evoked compound action potentials (PECAPs)

Purpose: Variations in neural survival along the cochlear implant electrode array leads to off-place listening, resulting in poorer speech understanding outcomes for recipients. Therefore, it is important to develop and compare clinically viable tests to identify these patient-specific intra-cochlea neural differences. Methods: We derived the neural health along the electrode array for a group of experienced adult implant recipients using two methods: the difference between psychophysical detection thresholds in bipolar vs. monopolar mode and the Panoramic electrically-evoked compound action potential method (PECAP). We hypothesised that: 1) the two neural measures will correlate at both the individual and group level; and 2) a larger variation in neural health along the electrode array will be associated with poorer speech understanding outcomes. Results: At the individual level, the two neural measures correlated significantly (p<0.05) for 5 out of 15 participants. At the group level, we observed a weak but significant correlation (R2=0.111, p<0.001) between the two neural measures. While a larger variation in neural measures derived from psychophysical thresholds was associated with lower phoneme speech scores (R2=0.499, p<0.01), no significant association was found between variations in PECAP’s neural health estimates and phoneme speech scores (R2=0.082, p=0.366). Conclusion: Our evidence suggests that both methods likely quantify a shared underlying neural basis, hypothesised to be the neural health along the cochlear implant array. The differences between the two measures may be attributed to differences in stimulus rate or loudness used to elicit responses and/or a combination of non-peripheral and non-neural confounds.