Assistive Technology for the Hearing-Impaired, Deaf and Deafblind

by Hersh, Marion A.; Johnson, Michael A.; Andersson, Conny; Campbell, Douglas; Farquharson, Alistair

• ISBN13: 9781852333829
• ISBN10: 1852333820
• Format: Hardcover
• Copyright: 2003-08-01
• Publisher: Springer Verlag

Summary

Affirmative legislative action in many countries now requires that public spaces and services be made accessible to disabled people. Although this is often interpreted as access for people with mobility impairments, such legislation also covers those who are hearing or vision impaired. In these cases, it is often the provision of advanced technological devices and aids which enables people with sensory impairments to enjoy the theatre, cinema or a public meeting to the full. Assistive Technology for the Hearin-impaired, Deaf and Deafblind shows the student of rehabilitation technology how this growing technical provision can be used to support those with varying reductions in auditory ability and the deafblind in modern society. Features: instruction in the physiology of the ear together with methods of measurement of hearing levels and loss; the principles of electrical engineering used in assistive technology for the hearing impaired; description and demonstration of electrical engineering used in hearing aids and other communications enhancement technologies; explanation of many devices designed for every-day living in terms of generic electrical engineering; sections of practical projects and investigations which will give the reader ideas for student work and for self teaching. The contributors are internationally recognised experts from the fields of audiology, electrical engineering, signal processing, telephony and assistive technology. Their combined expertise makes Assistive Technology for the Hearing-impaired, Deaf and Deafblind an excellent text for advanced students in assistive and rehabilitation technology and to professional engineers and medics working in assistive technology who wish to maintain an up-to-date knowledge of current engineering advances.

Table of Contents

1 Anatomy and Physiology of Hearing, Hearing Impairment and Treatment	1	(40)
1.1 Introduction	1	(3)
1.1.1 Learning Objectives	1	(1)
1.1.2 Overview of Hearing	2	(1)
1.1.3 The Auditory System in Engineering Terms	3	(1)
1.2 Acoustics of Hearing	4	(10)
1.2.1 Amplitude	6	(1)
1.2.2 Phase	7	(1)
1.2.3 Frequency and Period	8	(1)
1.2.4 Sound Intensity and the Decibel Scale	8	(1)
1.2.5 Simple and Complex Sounds	9	(1)
1.2.6 Spectral Analysis of Complex Sounds	10	(1)
1.2.7 Filtering Sound	10	(4)
1.3 Anatomy and Physiology of the Auditory System	14	(1)
1.3.1 Some Terminology Used in Describing Anatomical Structures	14	(1)
1.4 The Anatomy and Functions of the Outer-ear Structures	15	(3)
1.4.1 The Pinna	16	(1)
1.4.2 External Auditory Meatus	16	(1)
1.4.3 Functions of the Outer-ear Structures	17	(1)
1.5 The Anatomy and Functions of the Middle-ear Structures	18	(5)
1.5.1 The Tympanic Membrane	18	(1)
1.5.2 Middle-ear Ossicles	19	(1)
1.5.3 The Middle-ear Cavity	20	(2)
1.5.4 The Functions of the Middle-ear Structures	22	(1)
1.6 The Anatomy and Functions of the Inner-ear Structures	23	(4)
1.6.1 Vestibule	24	(1)
1.6.2 The Cochlea	24	(3)
1.6.3 Sound Processing in the Cochlea	27	(1)
1.7 The Central Auditory Nervous System	27	(2)
1.8 Classification of Hearing Loss	29	(7)
1.8.1 Degrees of Hearing Loss	31	(1)
1.8.2 Hearing Loss Due to Problems in the Outer Ear	31	(1)
1.8.3 Hearing Loss Due to Problems in Middle Ear	32	(1)
1.8.4 Hearing Loss Due to Problems in the Cochlea	32	(1)
1.8.5 Problems in the Auditory (Eighth) Nerve and Central Auditory Pathways	33	(3)
1.9 Medical and Non-medical Treatments	36	(1)
1.9.1 Medical and Surgical Treatment of Problems in the Auditory System	36	(1)
1.9.2 Non-medical or Non-surgical Interventions	36	(1)
1.10 Learning Highlights of the Chapter	37	(1)
Projects and Investigations	38	(1)
References and Further Reading	39	(2)
2 Audiology: The Measurement of Hearing	41	(30)
2.1 Introduction: The Measurement of Hearing	41	(1)
2.1.1 Learning Objectives	41	(1)
2.2 Measurement Systems	42	(2)
2.2.1 Definitions	42	(1)
2.2.2 Frequency-response Curves	43	(1)
2.2.3 Gain in Decibels	43	(1)
2.2.4 Amplifiers	44	(1)
2.3 Measurement of Biological Variables and Sources of Error	44	(2)
2.3.1 Types of Error	44	(1)
2.3.2 Physiological and Environmental Sources of Error	45	(1)
2.4 The Test Decision Process	46	(1)
2.5 Pure-tone Audiometry	47	(9)
2.5.1 Audiograms	47	(1)
2.5.2 Noise	48	(1)
2.5.3 The Test	48	(3)
2.5.4 Masking	51	(1)
2.5.5 Instrumentation	52	(1)
2.5.6 Technical Description of an Audiometer	53	(2)
2.5.7 Technical Specifications	55	(1)
2.6 Immittance Audiometry	56	(3)
2.6.1 Definitions	56	(1)
2.6.2 Measurement	57	(1)
2.6.3 Static Acoustic Immittance	58	(1)
2.6.4 Tympanometry	58	(1)
2.6.5 Acoustic Reflex Threshold	59	(1)
2.7 Electric Response Audiometry (ERA)	59	(2)
2.7.1 Electrocochleography	60	(1)
2.7.2 Brain-stem Response Audiometry	61	(1)
2.8 Standards	61	(1)
2.9 Audiometric Equipment Design and Calibration	62	(3)
2.9.1 Earphone Calibration	63	(1)
2.9.2 Calibration of Pure-tone Audiometers	64	(1)
2.9.3 Calibration of Couplers and Sound-level Meters	64	(1)
2.9.4 Calibration of Bone Vibrators	65	(1)
2.9.5 Calibration of Acoustic Immittance Devices	65	(1)
2.10 Artificial Ears	65	(3)
2.10.1 The 2cc Coupler	66	(1)
2.10.2 Zwislocki Coupler	67	(1)
2.10.3 KEMAR	67	(1)
2.11 Learning Highlights of the Chapter	68	(1)
Acknowledgements	68	(1)
Projects and Investigations	68	(1)
References and Further Reading	69	(2)
3 Hearing-aid Principles and Technology	71	(46)
3.1 Learning Objectives	71	(1)
3.2 Introduction	71	(9)
3.2.1 Review of Technical Terms	73	(1)
3.2.2 Human Hearing Viewed from an Engineering Perspective	73	(4)
3.2.3 Hearing-aid Prescription (in Brief)	77	(3)
3.3 Categories of Electronic Aids	80	(7)
3.3.1 Body-worn Aid	81	(1)
3.3.2 Behind-the-ear Aid	81	(2)
3.3.3 Spectacles Aid	83	(1)
3.3.4 In-the-ear Aid	83	(1)
3.3.5 Bone-conduction Aid	84	(1)
3.3.6 Middle-ear Implant Aid	85	(1)
3.3.7 Cochlear Implant Aid	85	(1)
3.3.8 Auditory Brain-stem Implant Aid	86	(1)
3.4 Historical Background	87	(1)
3.5 The Ear as an Environment	88	(3)
3.5.1 Aid-on-body Considerations	88	(2)
3.5.2 Body-on-aid Considerations	90	(1)
3.6 Processing Strategies	91	(15)
3.6.1 Single-channel Processing Schemes	91	(12)
3.6.2 Multiple-channel Processing Schemes	103	(3)
3.7 Modern Hearing-aid Technology	106	(3)
3.7.1 Analogue Hearing Aids	106	(1)
3.7.2 Digital Hearing Aids	106	(2)
3.7.3 Portable Speech Processors	108	(1)
3.8 Conclusion and Learning Highlights of the Chapter	109	(2)
3.8.1 Current Research	110	(1)
3.8.2 A Future Possibility?	110	(1)
3.8.3 Learning Highlights of the Chapter	110	(1)
Acknowledgements	111	(1)
Projects and Investigations	111	(2)
References and Further Reading	113	(4)
4 Induction-loop Systems	117	(36)
4.1 Learning Objectives	117	(1)
4.2 Audio-frequency Induction-loop Systems	117	(1)
4.3 The Electromagnetic Principles of a Loop System	118	(3)
4.4 Induction-loop Systems	121	(11)
4.4.1 Hearing-aid Receiver or Telecoil	121	(1)
4.4.2 The Effect of Different Materials and Loop Shapes	122	(1)
4.4.3 Magnetic Field Strength	123	(1)
4.4.4 Magnetic Field Direction	124	(1)
4.4.5 Magnetic Field Distribution	124	(4)
4.4.6 Overspill	128	(4)
4.5 Loop Installation	132	(4)
4.5.1 Multi combination Loop System	136	(1)
4.6 The Electrical Equivalent of a Loop System	136	(7)
4.6.1 Loop Inductance	137	(1)
4.6.2 Loop Resistance	137	(1)
4.6.3 Loop Impedance	137	(4)
4.6.4 Two-turn Loop	141	(2)
4.7 Automatic Gain Control	143	(3)
4.8 Loop System Measurements	146	(3)
4.8.1 The Dynamic Range of a Loop System	146	(1)
4.8.2 Magnetic Field Strength as a Function of Level and Frequency	147	(1)
4.8.3 Measurement of the Loop Amplifier	147	(1)
4.8.4 Field-strength Meters	148	(1)
4.9 Standards for Loop Systems	149	(1)
4.10 Learning Highlights for the Chapter	150	(1)
Projects and Investigations	151	(1)
References and Further Reading	152	(1)
5 Infrared Communication Systems	153	(24)
5.1 Learning Objectives and Introduction	153	(1)
5.1.1 Learning Objectives	153	(1)
5.2 Basic Principles	153	(5)
5.2.1 General Technical Requirements for Audio Applications	154	(1)
5.2.2 Applications	155	(2)
5.2.3 Technical Features and Application Requirements	157	(1)
5.3 System Components	158	(11)
5.3.1 Audio Sources and Signal Processing in the Transmitter	159	(1)
5.3.2 Radiators	160	(4)
5.3.3 Receivers	164	(5)
5.4 Compatibility and Use with Hearing Aids	169	(1)
5.5 Design Issues	169	(3)
5.5.1 System Placement	170	(1)
5.5.2 Interference Issues	170	(1)
5.5.3 Ergonomic and Operational Issues	170	(2)
5.6 Technical Standards and Regulations	172	(1)
5.7 Advantages and Disadvantages of Infrared Systems	172	(1)
5.8 Conclusions and Learning Highlights	173	(1)
5.8.1 Learning Highlights of the Chapter	173	(1)
Acknowledgements	173	(1)
Projects and Investigations	174	(1)
References and Further Reading	175	(2)
6 Telephone Technology	177	(38)
6.1 Introducing Telephony and Learning Objectives	177	(1)
6.2 User-centred Telephone Design	178	(2)
6.2.1 Designing for Hearing Impairment	178	(2)
6.2.2 Putting It All Together	180	(1)
6.3 Design of an Electronic Telephone	180	(15)
6.3.1 Introducing the Modern Telephone	182	(2)
6.3.2 Indication of the Start of the Call	184	(1)
6.3.3 Transmission of Signalling Information	184	(3)
6.3.4 Design of the Transmission Circuit	187	(3)
6.3.5 Call Arrival Indication (Ringing)	190	(2)
6.3.6 Telephone Design Enhancements to Provide Additional Accessibility Features	192	(3)
6.4 The Text Telephone	195	(8)
6.4.1 Introduction	195	(1)
6.4.2 Basic Principles	196	(7)
6.5 The Videophone	203	(7)
6.5.1 Basic Principles	203	(3)
6.5.2 Application Aspects	206	(2)
6.5.3 Systems and Standards	208	(2)
6.5.4 Future Systems	210	(1)
6.6 Conclusions and Learning Highlights	210	(2)
6.6.1 Learning Highlights of the Chapter	210	(1)
Projects and Investigations	211	(1)
References and Further Reading	212	(3)
7 Alarm and Alerting Systems for Hearing-impaired and Deaf People	215	(42)
7.1 Learning Objectives	215	(1)
7.2 The Engineering Principles of Alarm and Alerting Devices	215	(5)
7.2.1 Design Issues	216	(2)
7.2.2 Categorisation of Alarm and Alerting Systems	218	(2)
7.3 Sensors, Transducers and Actuators	220	(9)
7.3.1 The Sensors in Fire Alarms	221	(2)
7.3.2 Carbon Monoxide Sensors	223	(2)
7.3.3 Intruder Detectors	225	(1)
7.3.4 Piezoelectric Sensors: Sound and Pressure	226	(2)
7.3.5 Microphones: Sound Sensors	228	(1)
7.4 Signal Conditioning	229	(8)
7.4.1 Voltage and Power Amplifiers	230	(1)
7.4.2 Transistor	231	(2)
7.4.3 Voltage Amplifiers	233	(1)
7.4.4 Small-signal Tuned Amplifiers	234	(1)
7.4.5 Class C Power Amplifiers	235	(2)
7.4.6 Class AB Power Amplifiers	237	(1)
7.5 Radio Frequency Transmission	237	(9)
7.5.1 Transmitter	238	(1)
7.5.2 Superheterodyne Receiver	239	(2)
7.5.3 Modulation	241	(1)
7.5.4 Modulator	242	(2)
7.5.5 Demodulator	244	(2)
7.6 Actuators	246	(7)
7.6.1 Auditory Signals: Loud Bells and Buzzers	246	(1)
7.6.2 Lights	247	(1)
7.6.3 Light-emitting Diodes	248	(1)
7.6.4 Television	248	(1)
7.6.5 Vibro tactile Devices	249	(1)
7.6.6 Electro-tactile Devices	250	(1)
7.6.7 Paging Systems	250	(3)
7.7 Learning Highlights of the Chapter	253	(1)
Projects and Investigations	253	(1)
References and Further Reading	254	(3)
8 Dual Sensory Impairment: Devices for Deafblind People	257	(40)
8.1 Learning Objectives	257	(1)
8.2 Definitions and Demographics of Deafblindness	257	(1)
8.3 Communication for Deafblind People	258	(4)
8.3.1 Assistive Technology for Deafblind Communication	261	(1)
8.4 Braille Devices	262	(4)
8.4.1 Braille Displays	262	(1)
8.4.2 Multifunction Braille Notetakers	263	(1)
8.4.3 Text-Braille Conversion and Braille Embossers	264	(2)
8.5 Automating Fingerspelling for Deafblind Communication	266	(8)
8.5.1 Developing Mechanical Fingerspelling Hands for Deafblind People	266	(1)
8.5.2 Dexter I	267	(1)
8.5.3 Dexter II and III	268	(1)
8.5.4 Fingerspelling Hand for Gallaudet	268	(2)
8.5.5 Ralph	270	(1)
8.5.6 The Handtapper - a UK Development	271	(1)
8.5.7 Speaking Hands and Talking Gloves	272	(1)
8.5.8 Comparison and Availability	273	(1)
8.6 Other Communication Aids	274	(2)
8.6.1 The Optacon and Optical Character Recognition (OCR)	274	(1)
8.6.2 Tactile Sound-recognition Devices	275	(1)
8.7 Low-technology Devices and Domestic Appliances	276	(2)
8.8 Bluetooth	278	(1)
8.9 Alerting Devices for Deafblind People	279	(5)
8.9.1 Vibrating Alarm Clocks	280	(2)
8.9.2 A Multifunction Domestic Alert System	282	(2)
8.9.3 Tactiwatch	284	(1)
8.9.4 Tam	284	(1)
8.10 Access to Information Technology	284	(2)
8.10.1 The Universal Communications Text Browser (Ucon)	286	(1)
8.11 Provision of Telecommunications Equipment and Services	286	(4)
8.11.1 Hardware	287	(2)
8.11.2 Software and Access to Telecommunications	289	(1)
8.12 Future Research Directions	290	(2)
Projects and Investigations	292	(1)
References and Further Reading	293	(4)
9 The Final Product: Issues in the Design and Distribution of Assistive Technology Devices	297	(10)
9.1 Development and Distribution of Devices	297	(2)
9.2 Working with End Users	299	(2)
9.2.1 Methods for Involving End Users	300	(1)
9.2.2 FORTUNE Concept of User Participation in Projects	300	(1)
9.3 Communication Issues	301	(1)
9.4 Other Important Issues	302	(2)
9.4.1 Deaf Culture and Deaf Awareness	302	(1)
9.4.2 Ethical Issues	303	(1)
9.4.3 Data Protection Legislation	304	(1)
Acknowledgements	304	(1)
References and Further Reading	305	(2)
Biographies of the Contributors (in Alphabetical Order of Family Name)	307	(6)
Index	313