Principles of Hearing Aid Audiology

Principles of Hearing Aid Audiology

Principles of Hearing Aid Audiology Maryanne Tate I a 11 I Springer-Science+Business Media, B. v.

First edition 1994 Maryanne Tate 1994 Originally published by Maryanne Tate in 1994 ISBN 978-0-412-49070-5 ISBN 978-1-4899-7152-4 (ebook) DOI 10.1007/978-1-4899-7152-4 Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the UK Copyright Designs and Patents Act, 1988, this publication may not be reproduced, stored, or transmitted, in any form or by any means, without the prior permission in writing of the publishers, or in the case of reprographic reproduction only in accordance with the terms of the licences issued by the Copyright Licensing Agency in the UK, or in accordance with the terms of licences issued by the appropriate Reproduction Rights Organization outside the UK. Enquiries concerning reproduction outside the terms stated here should be sent to the publishers at the London address printed on this page. The publisher makes no representation, express or implied, with regard to the accuracy of the information contained in this book and cannot accept any legal responsibility or liability for any errors or omissions that may be made. A catalogue record for this book is available from the British Library Printed on permanent acid-free text paper, manufactured in accordance with ANSIINISO 239.48-1992 and ANSI/NISO 239.48-1984 (Permanence of Paper).

Contents Foreword Acknowledgements ix X PART ONE Fundamental Sciences 1 Acoustics 1.1 Physical properties of sound 1.2 The measurement of sound 1.3 The audiometer 1.4 The psychological properties of sound 1.5 Summary 2 Anatomy and physiology of the ear 2.1 Anatomy of the ear 2.2 The physiology of hearing 2.3 Summary 3 Medical aspects of hearing loss 3.1 Introduction 3.2 Pathology of the outer ear 3.3 Pathology of the middle ear 3.4 Pathology of the inner ear 3.5 Other conditions of the ear 3.6 Summary 4 Speech and intelligibility 4.1 The speech chain 1 3 3 10 14 17 18 19 19 20 20 32 39 40 41 41 42 46 50 57 59 60 60 61 61

vi Contents 4.2 The vocal tract 63 4.3 Speech-reading 64 4.4 Speech sounds 65 4.5 Hearing loss and speech perception 70 4.6 Hearing loss and speech production 71 4. 7 Summary 72 72 5 The hearing aid system 73 5.1 The basic components of a hearing aid 73 5.2 Elementary electricity and electronics 84 5.3 Signal processing 86 5.4 Summary 93 94 94 PART TWO The Practice of Hearing Aid Audiology 95 6 The assessment procedure 97 6.1 Pre-selection management 97 6.2 Otoscopy 101 6.3 Tuning fork tests 103 6.4 Principal audiometric tests 106 6.5 Understanding audiograms 117 6.6 Room requirements for audiometry 122 6.7 Summary 123 124 125 7 Hearing aids and their performance 126 7.1 Introduction 126 7.2 Types of hearing aid system 127 7.3 Specification and performance 132 7.4 Hearing aid standards 139 7.5 Measuring methods 142 7.6 Power sources 146 7.7 The National Health Service provision of hearing aids 149 7.8 Summary 152 153 153 8 Selection and fitting 155 8.1 The choice of a hearing aid system 155 8.2 Hearing aid fitting 163

Contents vii 8.3 Summary 9 Earmoulds 9.1 Making the impression 9.2 Earmoulds 9.3 Summary 10 Evaluation 10.1 Introduction 10.2 Insertion gain measurement 10.3 Functional gain measurement 10.4 Speech audiometry 10.5 Subjective evaluation 10.6 Summary 11 Client management and rehabilitation 11.1 The rehabilitation process 11.2 Practical aspects of rehabilitation 11.3 Assistive devices for the hearing impaired 11.4 Management practices 11.5 Improving communications 11. 6 The role of other specialists 11.7 Summary 171 171 172 173 173 178 185 185 186 187 187 187 190 191 197 199 199 200 201 201 207 213 214 217 219 220 220 221 PART THREE Special Aspects of Hearing Aid Audiology 223 12 Assessment and management of special problems 225 12.1 Tinnitus 225 for section 12.1 232 for section 12.1 232 12.2 Impedance audiometry 232 for section 12.2 240 12.3 Specialized audiometric tests 240 for section 12.3 246 for section 12.3 246 12.4 Non-organic hearing loss 246

viii Contents for section 12.4 for section 12.4 12.5 Automatic audiometry for section 12.5 for section 12.5 13 Paediatric provision 13.1 The effect of hearing loss in children 13.2 Habilitation of hearing impaired children 13.3 Summary Appendix Glossary Index 249 250 250 252 252 253 253 259 264 264 265 266 277

Foreword Both for those in training towards qualification in hearing aid audiology and for those simply wishing to revise and update their knowledge, it is a perennial problem to acquire one book which provides comprehensive and up-to-date material on hearing aid audiology. Principles of Hearing Aid Audiology meets the need for a text book which deals not only with the foundation sciences of hearing aid audiology but also the many and varied aspects of audiological practice where the objective is the rehabilitation of the hearing impaired through hearing aid prescription and fitting. In bringing together all the material contained in this book, Maryanne Tate has drawn on her considerable experience in the training of hearing aid audiologists as well as in dealing with the hearing impaired themselves. As a result, this book has total relevance to the needs of the many professional groups whose work brings them into contact with the hearing impaired. The very practical nature of hearing aid audiology is fully recognized so that the purely theoretical aspects are presented and explained with a view to supporting hearing aid audiology in practice. With so many audiology text books emanating from the USA, Principles of Hearing Aid Audiology will, I am sure, be greatly welcomed by readers in the UK. Undoubtedly, this book will feature prominently on any list of recommended reading in audiology and, at the same time, will serve as a very useful work of reference. Barry Downes, LLB, FSHAA Registrar of the Society of Hearing Aid Audiologists, 1988-1993

Acknowledgements Many colleagues and friends have helped and encouraged me to write this book. Dr Mark Lutman (Institute of Hearing Research, Nottingham) provided both critical comments and encouragement when I needed them in the early stages, and I am particularly grateful for the contributions of: Dr Loraine Lawrence, S.C.M.O. Audiological Medicine, Tameside Area Health Services Mr Joseph Rumble, Consultant Oral Surgeon, North Middlesex Hospital Mr Peter Grimaldi, Consultant ENT Surgeon, StMary's Hospital, Isle of Wight Mr Robert Rendell, Training Officer, Hidden Hearing Ltd, and Registrar of the Society of Hearing Aid Audiologists Dr Derek Tate, Associate Head of Centre for Design, Manufacture and Technology, University College Salford. I appreciate the assistance given by Roy Sands (Special Projects Manager, Rayovac UK Ltd) and Julian Parmenter (Technical Sales Manager, Duracell UK Ltd) with regard to battery specifications. I should also like to express my sincere thanks to all those who read and commented on part, or all, of the manuscript, especially Neville Browne (Director, The London Otological Centre), Keith Attenborough (Professor of Acoustics, The Open University), Barry Downes (Managing Director, SieTech Hearing Ltd), David Gaszczyk (Audiologist, BMI Healthcare), John Millership and Alan Hall (Hearing Aid Audiologists, Amplivox and Ultratone Ltd). Finally my thanks must go to Dorothy Rothwell who word-processed the manuscript and tolerated my many revisions without complaint, John Beeton and other colleagues and friends who helped me in many ways, and to all those friends and family who endured my preoccupation throughout 1992 and 1993, especially my children Kerry, Joanne, Christopher and Russell.