Deriving Cochlear Delays in Humans Using Otoacoustic Emissions and Auditory Evoked Potentials
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i “PhDThesis_Master” — 2009/1/9 — 10:55 — page i — #1 i i i Deriving cochlear delays in humans using otoacoustic emissions and auditory evoked potentials Ph.D. thesis by Gilles Pigasse Technical University of Denmark 2008 i i i i i “PhDThesis_Master” — 2009/1/9 — 10:55 — page ii — #2 i i i Copyright c Gilles Pigasse, 2008 ISBN 978-87-911-8489-5 Printed in Denmark by Hillerød Grafisk. i i i i i “PhDThesis_Master” — 2009/1/9 — 10:55 — page iii — #3 i i i Contents Preface vii Abstract ix List of abbreviations and symbols xiii 1 Introduction1 1.1 Project motivation and objectives....................2 1.2 Contributions of the thesis.......................4 2 Background and theory5 2.1 Otoacoustic emissions.........................5 2.1.1 Generation mechanisms....................8 2.1.2 Effect of external factors on OAEs...............9 2.1.3 Clinical usage of OAEs..................... 10 2.2 Auditory evoked potentials....................... 10 2.2.1 Auditory brainstem responses................. 14 2.2.2 Auditory steady-state responses................ 17 2.2.3 Comparison between ASSRs and ABRs............ 20 2.3 Summary................................ 21 3 Individual cochlear delay estimates using otoacoustic emissions 23 3.1 Introduction............................... 24 3.2 Methods................................. 25 i i i i i “PhDThesis_Master” — 2009/1/9 — 10:55 — page iv — #4 i i i iv Contents 3.2.1 Subjects............................. 25 3.2.2 Stimulus generation and response measurement........ 25 3.2.3 Off-line data analysis...................... 28 3.3 Results.................................. 35 3.3.1 Effect of frequency on TBOAE latency............ 35 3.3.2 Intra-subject variability..................... 38 3.3.3 Inter-subject variability..................... 40 3.3.4 Effect of the noise floor on OAE latency............ 41 3.3.5 Comparison of TBOAE latency with previous studies..... 43 3.4 Discussion................................ 44 3.4.1 Conclusion........................... 47 4 Individual estimates of brainstem response delays 49 4.1 Introduction............................... 49 4.2 Methods................................. 51 4.2.1 Subjects............................. 51 4.2.2 Stimuli............................. 51 4.2.3 Procedure............................ 52 4.2.4 TBABR latency and interpeak delays............. 53 4.3 Results.................................. 55 4.3.1 wave-V latency......................... 55 4.3.2 Intra- and inter-subject variability............... 57 4.3.3 Interpeak intervals....................... 59 4.4 Discussion................................ 60 4.4.1 Rise time difference...................... 62 4.4.2 Level difference........................ 62 4.4.3 Subject gender difference.................... 63 4.4.4 Summary............................ 63 5 Comparison of OAE and ABR estimates of cochlear delay 65 5.1 Introduction............................... 66 5.1.1 Acoustic wave hypothesis................... 66 5.1.2 Coherent Reflection Filtering theory.............. 66 i i i i i “PhDThesis_Master” — 2009/1/9 — 10:55 — page v — #5 i i i Contents v 5.1.3 Signal-front hypothesis..................... 67 5.2 Results.................................. 68 5.2.1 Intra-subject variability..................... 70 5.2.2 Inter-subject variability..................... 70 5.2.3 Acoustic wave hypothesis................... 71 5.2.4 CRF theory........................... 72 5.2.5 Signal-front hypothesis..................... 75 5.3 Discussion................................ 77 5.3.1 Separating the analysis below and above 2 kHz........ 78 5.3.2 Scaling symmetry....................... 80 5.4 Conclusion............................... 82 6 Individual steady-state response delays 85 6.1 Introduction............................... 85 6.2 Methods................................. 87 6.2.1 Subjects............................. 87 6.2.2 Stimuli and recording procedure................ 88 6.2.3 Response detection....................... 89 6.2.4 ASSR latency.......................... 90 6.3 Results.................................. 91 6.3.1 Latency-frequency functions.................. 91 6.3.2 Intra-subject variability..................... 93 6.3.3 Comparison with previous studies............... 93 6.4 Discussion................................ 95 6.4.1 Comparison with ABR..................... 95 6.4.2 Gender difference........................ 98 6.5 Conclusion............................... 99 7 Chirp-evoked otoacoustic emissions 101 7.1 Introduction............................... 101 7.2 Methods................................. 104 7.2.1 Subjects and procedure..................... 104 7.2.2 Stimuli............................. 105 i i i i i “PhDThesis_Master” — 2009/1/9 — 10:55 — page vi — #6 i i i vi Contents 7.2.3 Time-frequency distribution.................. 106 7.3 Results.................................. 108 7.3.1 OAE time series........................ 108 7.3.2 Time-frequency analysis.................... 111 7.4 Discussion and conclusion....................... 114 8 Overall discussion 115 8.1 Summary of the main results...................... 115 8.2 Discussion................................ 117 8.3 Implications and future work...................... 119 Bibliography 123 Appendix 139 A Tone bursts: time and frequency plots 141 B Stimuli calibration 145 C Mathematical tools 147 C.1 Hilbert transform............................ 147 C.2 The least-squares fit time-domain filtering............... 148 C.3 Short-time correlation coefficient.................... 148 C.4 Pearson product moment correlation coefficient............ 149 D TBOAE and TBABR latencies 151 E Effect of tone burst rise time on wave-V latency 153 F Acoustic wave theory results 157 G CRF results 159 H Front delay results 161 I Individual ASSR latencies 163 i i i i i “PhDThesis_Master” — 2009/1/9 — 10:55 — page vii — #7 i i i Preface This thesis was submitted to the Technical University of Denmark (DTU) as partial and final fulfillment of the requirements for the degree of Doctor of Philosophy (Ph.D.) in Electronics and Communication. The work presented in this thesis was completed between October 1, 2004 and July 31, 2008 at the Centre for Applied Hearing Research (CAHR), Department of Electrical Engineering, DTU and at the Institute of Sound and Vibration Research (ISVR), Southampton University, England. The work was done under the supervision of Prof. Torsten Dau and Dr. James Harte. A public defense was held on December 3, 2008. The project was jointly funded by GN ReSound A/S, Oticon A/S and Widex A/S and the external stay at ISVR was supported by a Marie Curie Research Fellowship via the European Doctorate in Sound and Vibration Studies. Ethical considerations for conducting the experiments at DTU were made with respect to the Scientific Ethics Committee of Copenhagen County, file number KA 04159g, experiments made at ISVR were approved by the departmental Safety and Ethics Committee of this institute. Every chapter presenting experimental results contains, prior to its introduction, an abstract, which is intended for the reader to have a rapid overview of the work presented herein. A list of the main abbreviations and symbols used in this thesis is available before the table of content. The appendices contain plots, tables and explanations that are not crucial to understand the main part, but can be referred to for more details about the experimental work. The work described in this thesis could not have been completed without the help and support of many people, I would like to thank my two supervisors Torsten and James for guiding me through this project, especially during times of immense doubt. i i i i i “PhDThesis_Master” — 2009/1/9 — 10:55 — page viii — #8 i i i viii Preface Thanks also to Manfred Mauermann and his colleagues at the Haus Des Hörens and the University of Oldenburg, for welcoming me in their group during three months, making interesting suggestions and for a fruitful collaboration when writing the OAE software. Thanks to Steve Bell and his colleagues from the Hearing and Balance Centre at Southampton University for a pleasant and useful stay. Thanks to my colleagues in CAHR, especially Tobias Piechowiak and Jens Bo Nielsen for keeping a nice atmosphere in the office, Iris Arweiler and Brent Kirkwood for proofreading part of this work and providing useful advice. Thanks also to the 55 (or so) test persons for their patience and their will to sleep for hours during the experiments, even if not all data could be used at the end. Gilles Pigasse January 7, 2009 i i i i i “PhDThesis_Master” — 2009/1/9 — 10:55 — page ix — #9 i i i Abstract A great deal of the processing of incoming sounds to the auditory system occurs within the cochlear. The organ of Corti within the cochlea has differing mechanical properties along its length that broadly gives rise to frequency selectivity. Its stiffness is at maximum at the base and decreases towards the apex, resulting in locally resonant behaviour. This means high frequencies have maximal response at the base and low frequencies at the apex. The wave travelling along the basilar membrane has a longer travel time for low-frequency stimulus than for high-frequency stimulus. The intrinsic relation between frequency and travel time in the cochlea defines the cochlear delay. This delay is directly associated with the signal analysis occurring in the inner ear and is therefore of primary interest to get a better knowledge of this organ. It is possible to estimate the cochlear delay by direct and invasive