ECAP measures predict cochlear implant behavioural thresholds

.................................................................................................................................................................................................................... 7 Abbreviations ......................................................................................................................................................................................................... 8 Background ............................................................................................................................................................................................................ 9 Introduction ...................................................................................................................................................................................................... 9 Cochlear implants ....................................................................................................................................................................................... 10 The normal cochlea ............................................................................................................................................................................. 10 Hearing loss ............................................................................................................................................................................................. 11 Sound processing.................................................................................................................................................................................. 12 CI stimulation ........................................................................................................................................................................................... 13 Neural responses to electrical stimulation .............................................................................................................................. 16 ECAPs ................................................................................................................................................................................................................. 17 ECAP stimulation and response .................................................................................................................................................... 17 Artefact isolation ................................................................................................................................................................................... 19 The use of ECAPs in fitting cochlear implants ........................................................................................................................ 20 The effect of rate on behavioural levels ......................................................................................................................................... 22 Unexplored potential for correlation between ECAPs and behavioural levels .......................................................... 25 The Δlatency effect .............................................................................................................................................................................. 25 The IPG and PD effects ....................................................................................................................................................................... 26 Our experiment .................................................................................................................................................................................................. 27 Methods ................................................................................................................................................................................................................. 28 Subjects ............................................................................................................................................................................................................ 28 Procedures ..................................................................................................................................................................................................... 29 Electrophysiological measurements .......................................................................................................................................... 30 Behavioural measures ............................................................................................................................................................................. 32 Analysis ............................................................................................................................................................................................................ 32 Behavioural data ................................................................................................................................................................................... 32 3 Average linear shift to equalise amplitude .............................................................................................................................. 33 N1 peak latency ..................................................................................................................................................................................... 35 Average shift in latency ..................................................................................................................................................................... 37 ECAP threshold ............................................................................................................................................................................................. 38 Correlations .................................................................................................................................................................................................... 38 Stepwise regression .................................................................................................................................................................................. 38 Results .................................................................................................................................................................................................................... 39 ECAP presence.............................................................................................................................................................................................. 39 Behavioural threshold changes .......................................................................................................................................................... 41 ECAP threshold and behavioural threshold correlations ....................................................................................................... 42 PD and IPG amplitude effects .............................................................................................................................................................. 43 All subject correlations ....................................................................................................................................................................... 43 Normalised correlations .................................................................................................................................................................... 45 Subject mean correlations ............................................................................................................................................................... 46 Latency effects............................................................................................................................................................................................. 47 All subject correlations ....................................................................................................................................................................... 47 Normalised correlations .................................................................................................................................................................... 49 Subject mean correlations ............................................................................................................................................................... 50 Stepwise regression to estimate 1000 pps thresholds ........................................................................................................... 51 Discussion ............................................................................................................................................................................................................. 53 High rate threshold change variability ........................................................................................................................................... 53 PD and IPG amplitude effects .............................................................................................................................................................. 54 ΔLatency effects ......................................................................................................................................................................................... 56 Stepwise regression model.................................................................................................................................................................... 59 Limitations and improvements ........................................................................................................................................................... 60 Conclusion ............................................................................................................................................................................................................ 64 References ............................................................................................................................................................................................................ 65 Appendix 1............................................................................................................................................................................................................ 73 Behavioural threshold changes .......................................................................................................................................................... 73 PD and IPG amplitude effects .............................................................................................................................................................. 74 All subject correlations ....................................................................................................................................................................... 74