Cook Ch. 14 (p. 352 - 373)
BTE and Open Fit Hearing Aid
- A wire runs to a speaker that fits into the ear canal but does not block out the sounds that are normally heard. - Receiver in the canal (RIC) - Receiver is connected to the body of the BTE hearing aide via a wire running down a thin tube. - Open Fit used for individuals with hearing loss associated with aging.
Amplitude (projection) threshold for normal hearing
- Adults 25 dB - Children 15 dB
Air Conduction Hearing Aids
- Behind the Ear (BTE) - In the Ear( ITE) - Completely in the Canal (CIC) - Body Level Aids
Hearing loss is variable across frequencies
- Design of digital hearing aids accounts for this - Response to frequency is programmed using measured thresholds
Approaches with auditory impairments provides
- Feedback (visual or tactile) that represent the individuals speech patterns - Alternatives to oral communication (visual displays)
BTE
- Fit behind the ear and contain a microphone, amplifier, receiver, and a power supply - Switch is located on the back of the case
Hearing Pathway Augmentation Using Existing Pathways
- Hearing aids - Cochlear Implants - Bone anchored Hearing Aids (BAHA) - Assistive listening devices (ALDs)
Voice Over Internet Protocol (VoIP)
- Internet based telephone services - Advantageous due to lower cost, inclusion of multimedia, common features associated with cell phones/land-based lines (voicemail, caller ID, 3 way calling)
CIC
- Located 1-2 mm into the canal with speaker close to tympanic membrane
ITE
- Located in the opening to the ear canal - Microphone located in the face plate (provided a more natural location for microphone)
Sound amplification of a telephone is sufficient for some individuals.
- Many hearing aids have a telecoil that can be coupled to a telephone - Can also link Bluetooth devices with hearing aids and cochlear devices
Hearing Aid Output
- Measured in decibels (dB) - Sound Pressure Levels (SPLs) -designation given to hearing aid output - Average conversation can range from 40 to 80 db SPL
BTE - MTO
- Microphone - Telecoil (for telephone) - Off Switch
Cochlear User Results
- Most post-lingually deaf individuals obtain some degree of open set speech perception - In deaf children it has been show to facilitate development of language - Individuals with unilateral cochlear implants have more difficulty with auditory localization - Can provide children with environmental awareness
Frequency (pitch)
- Range heard by a human 20 to 20,000 Hz - Ear is most sensitive to (250 to 8000 Hz)
Disadvantages of Voice Over Internet Protocol - regarding accessibility.
- Relay operator is not mandated for a VoIP (it is for PSTN) - TTY messages can get garbled due to heavy traffic on networks - Many TTY cannot connect to VoIP - Voice quality may vary (which effects HOH individuals)
Tactile Substitution
- Sequence of sounds translated into tactile information and presented to user - Tactile information detected and assembled into meaningful units by CNS - Tactile information requires spatial and temporal information - Rate of input is slower than auditory
Cochlear Implant Criteria
- Severe or profound bilateral pure tone hearing loss (>90 dB) - Sentence recognition scores of less than 30% - Age 2 years or more with >90dB loss
Alternative Sensory Pathways
- Sign language - Tactile subsitution - Tadoma Method
Mobile Phone must meets 6 broad needs for deaf individuals
- Social - Safety - Communication - Transportation - Consumption - Entertainment
Communication between a nondisabled and an individual both deaf/visually impaired
- Standard keyboard and visual display for the non-disabled - A braille keyboard and display for the person who is deaf/blind
Visual Substitution
- Use of an oscilloscope to aid a deaf individual learning to speak ~ Not practical for assistive technologies - Use of Visual Alarms (flashing lights with a telephone or doorbell rings) - Use of Text Labels for computer generated synthetic speech - Design goal for assistive devices ~ Speech to text conversion > Speech is received and converted by computer to text > Text displayed for the individual with an auditory impairment.
Two basic approaches to using sensory assistive technologies
1. Augmentation of an existing pathway 2. Use of an alternative pathway - Tactile & Visual
Four types of hearing loss
1. Conductive Loss 2. Sensorineural Loss 3. Centrally Induced Damage 4. Functional Deafness
Two major parts of cochlear implants
1. External: Microphone (environmental sensor), electronic processing circuits, and a transmitter than couples information to the skull 2. Internal: Electrode array, a receiver, and electronic circuits that provided proper synchronization and stimulation parameters for the electrode array
Primary ways to use TTY
1. If both parties have a TTY, then each simple types their message and sends a "go ahead" (GA) command to indicate they are finished - Some device have a GA button to push 2. If a deaf person needs to communicate with a person without a TTY, an operator is used > Voice Carry Over: used for individuals who can speak but not hear > Hearing Carry Over: Used for individuals who can hear but not speak > Short Message Services (SMS): text communication that enables messaging using cell phones
Two major effects of auditory impairment
1. Loss of input information 2. Inability to monitor speech output
Telephone Devices for the Deaf
1. Teletype devices (TTY) originally used by individuals that are deaf. - Provided a visual telephone for sending weather and news information u 2. Models of current TTY are lightweight, battery-powered and portable - Uses > Keypad > Visual displays > Modem
Visual Telephones for the Deaf
1. Visual sign language - Comparable to the rate of human speech - Requires both parties to understand sign language 2. Visual Telephone - Interpreter can be video conferenced
Successful fitting of hearing aids
Relies on speech intelligibility, rather than sound levels
If both deaf and blind
Rely on use of tactile input about the environment - Tadoma Method - Finger Spelling
Functional Deafness
Results from perceptual deficits rather than physiological conditions
Auditory impairment ranges (slight - extreme)
Slight: 20 to 30 dB Mild: 30 to 45 dB Moderate: 60 to 75 dB Profound: 75 to 90 dB Extreme: 90 to 110 dB
Tadoma Method
The only tactile method for input of auditory information - Indicated for both deaf and blind (used by Hellen Keller) - The individual perceives information by placing hands on the speaker's face with the thumbs on the lips, index fingers on the sides of the nose, little fingers on the throat, and other fingers on the cheek - Fingers detect movement of the lips, nose, and cheeks and feels vibration of the larynx in the throat
Large Group Devices
Under the ADA large meeting rooms (concert halls, lecture auditorium, churches) but be equipped with assistive listening devices
Computer Assisted Real time (CART)
Used in lectures or meetings where there is one deaf participant - A stenographer translates speech into text
Individuals with severe hearing loss (sound amplification doesn't work) require
a device that visually send and receive telephone information
Captioning
is the process of converting audio into written words which appear on a screen
Closed Captioning
words are not visible unless the viewer has a closed captioning decoder
Structure of Hearing Aids
1.Environmental Sensor (microphone) - Can be Omnidirectional or Bidirectional 2.Information Processor (amplifier) - Amplification of the input signal with a frequency response that is matched to speech signals - Limits loud input signals to prevent distortion and discomfort for the user 3.Signal processing is provided to minimize noise and maximize the speech signal
Large Group Device Approaches
1.Hard-wired jacks for plugging in earphones 2.FM transmitter-receiver set-up 3.Audio induction loops for transmission to hearing aids equipped with telecoils
Computer Assisted Note Taking (CAN)
A fast typist enters text with a standard computer keyboard and with use of abbreviations to maximize the speed of data entry
Altering Devices for deaf
Individual needs to recognize a variety of environmental "sounds" - Doorbell - Fire alarm - Telephone - Traffic noises (ambulance, car horns)
Small Group Applications for the Classroom
Acoustic parameters affect speech perception 1.Signal to Noise Ration (SNR) 2.Reverberation Time (RT) 3.Distance from speaker
Hearing Aids
Amplify sound, primarily speech
Sensorineural Loss
Associated with defects in the cochlea and/or auditory nerve
Conductive Loss
Associated with pathological defects of the outer and/or middle ear
cochlear implant
Auditory prosthesis is used when there is damage to the cochlea of the inner ear - Provides some sound perception (cranial nerve 8 must be intact. Stimulation proved by use of implanted electrodes)
Measurement of Auditory Function
Auditory thresholds - amplitude - frequency
Bone Conduction Hearing Aids
BAHA: surgically attached to the skull and osseointegration during healing covers the implant with bone tissue - Become stable 3 weeks after surgery - Input to this type are converted to mechanical waves that vibrate the skull - Challenges include: localization (for some users), phone use, and lack of ongoing support
Causes of hearing loss
Congenital Physical Damage Disease Aging Effects of Medications
Types of Hearing Aids
Conventional Hearing Aids - Air conduction - Bone conduction
Acoustic Energy v. Speech Intelligibly
In book
Centrally Induced Damage
Damage to the auditory cortex of brain
Sign Language
Deafness - Most common: Manual Sign Language - Uses visual substitution
Audiologist
Determine the degree and the type of hearing loss
Assistive Listening Devices
Devices intended to be used in group settings that amplify sound and broadcast to receivers worn by a person who is hard of hearing.
Captioning fully accessible
Effective January 1, 1998: all television programs must be "fully accessible" - Meaning: 95% of the nonexempt programming must be closed caption
Small group device
Have multiple receivers for one transmitter if there is more than one person requiring amplification
