Chapter 7 Hearing Aids and Hearing Assistance Technologies
Purpose of Listening Devices • Make speech audible • Make non-speech audible • Restore range of loudness
Hearing Challenges • Hearing soft speech • Hearing speech clearly • Hearing speech in noisy environment • Hearing speech in reverberant environment
Definition of Hearing Aid • Hearing Aids(noun, plural) 1(archaic): electronic devices usually worn by a person for amplifying sound before it reaches the auditory receptor organs. 2(modern): electronic devices worn by a person for processing sound to provide audibility and improve the signal-to-noise ratio before it reaches the auditory receptor organs. A New Definition for Modern Hearing Aids, Victor Bray, Ph.D. & Michael Nilsson, Ph.D., Auditory Research Department, Sonic Innovations, Inc.
Types of Listening Devices • Hearing Aids • ALDs/HAT • Alerting Devices • Brainstem Implants • Bone Anchored Hearing Aids (BAHA) • Cochlear Implants (CI)
Hearing Aid Styles • Air conduction • Body Aid • Glasses • BTE • RITE • RITA • ITE • ITC • CIC • Bone Conduction • Bone Anchored (BAHA) (above 20 years) (now considered a mastoid implant)
Open Canal • Receiver in the Ear • RITE • Receiver in the Aid • RITA
Bone conduction HA • When a conventional hearing aid cannot be worn due to microtia, atresia, obstruction in EAM, bone conduction hearing aids may be beneficial
BAHA Bone Anchored Hearing Aid: • Surgically embedded titanium "post" into skull with a small abutment • A sound processor sits on abutment • The implant vibrates the skull and stimulates the cochlea via bone conduction bypassing outer & middle ear • Treatment for: • Conductive loss • Mixed hearing losses • Unilateral sensorineural hearing loss, • Chronic ear infections • Congenital external auditory canal atresia
Hearing Aids • Analog (conventional) • Programmable (analog or digital) • Digital
Analog hearing aids pick up the sound and convert it into electronic signals. These hearing aids have trimmers that are manually adjusted by a hearing healthcare professional using a tiny screwdriver. Analog hearing aids are the least flexible, but also the least expensive, level of hearing aid technology. Programmable Programmable hearing aids must be connected to a computer in order for your hearing healthcare professional to make adjustments. These hearing aids offer more flexibility and can provide more features. Digital Digital hearing aids contain computer chips that convert the electronic signal into digital signals. The digital hearing aid can perform complex processing of the sound, such as reducing the intensity of loud background noise. Typically programmed via a computer, offers the greatest flexibility in its ability to match the hearing aid response to the hearing loss. Type of Hearing Aids
HA Components MicrophoneThe microphone picks up sounds from the air and convert them into electrical signals.AmplifierThe amplifier increases the intensity of the signals from the microphone. Filters modify the sounds so that only sounds which are relevant for the person are amplified.'Loudspeaker' (Receiver)The third basic component is the 'loudspeaker' (receiver). It converts electrical signals into acoustic signals, which the person then hears.Small computer (Digital) (How it works)These three components exist in all hearing aids. Furthermore, in digital hearing aids a small computer can be programmed to manipulate the signals to fit the hearing loss of the individual hearing-impaired person.
Batteries • Various Sizes • Chemical
Earmolds • Earmolds direct sound into the ear canal • Variety of styles, colors, and other characteristics
Verification of HA • Real Ear (probe microphone) • Speech tests (HINT, QuickSIN, BKB-SIN, SPIN) • Subjective ratings of intelligibility and quality • Loudness verification • Questionnaires • Functional gain • ABR—for infants & young children
Probe Microphone • Real Ear measures of sound pressure in the ear canal
Speech Tests • HINT • QuickSIN • BKB-SIN • SPIN
QuickSIN/BKB-SIN 1.SNR loss of 0-2 dB: Normal to near-normal.These patients will probably do well in noise with any hearing aids that provide undistorted output. With directional microphones, they may hear better than their normal-hearing peers in noisy situations. 2. SNR loss of 2-7 dB: Mild SNR loss.Today’s directional microphones provide SNR improvements of 2 to 5 dB; with directional microphones, these patients should be able to hear almost as well as their normal-hearing counterparts in noisy situations. 3. SNR loss of 7-15 dB: Moderate SNR loss.While directional microphones will provide benefit for these patients, they cannot provide enough SNR improvement to allow the person to hear as well as their normal-hearing counterparts in noisy situations. Microphone arrays, such as the LinkiT, provide a 7 to 13 dB improvement in SNR. 4. SNR loss greater than 15 dB: Severe SNR loss. These patients need the maximum amount of SNR improvement, and FM systems are the technology of choice for these patients. Today’s ear-level FM systems are cosmetically appealing and are available in a wide range of hearing aids. Contact hearing aid manufacturers for more information.
Subjective Ratings • Magnitude Production • Pt is given a number and instructed to adjust a given parameter such as intensity, SNR, until that number is reached • Category Scaling • Pt is given a bounded scale such as 1 to 10 and asked to make a judgment of a speech passage based on intelligibility, quality, etc. • Paired Comparisons • Pt compares 2 different settings or hearing aids • Clarity • Pt asked to judge if sound is clear, distinct, pure…the opposite is diffuse
Loudness Restoration • PAL • Soft, comfortable, loud
Functional Gain • Compare Aided vs. Unaided results • In the example, the aided (green) thresholds are compared to the unaided thresholds for the right (red) and left (blue) thresholds
Questionnaires • APHAB • PAL
Binaural vs. Monaural Advantage • head shadow • loudness summation • localizing • signal to noise ratio
ALDS/HAT • Loop Induction (Loop)(Electromagnetic) • Radio Frequency • AM • FM • FM plus Video • BlueTooth • Light (Infrared)
ALDs/HAT Loop Induction Systems
Looping the World with Audiocoil • “The ordinary telecoil is perhaps the most common and most underestimated assistive listening device available for hearing impaired individuals today.” • Ross (2002). • “By changing the label to something more general—my suggestion is ‘audiocoil’—we do not restrict to a single function the way we think of the coil”. • Ross (2006). Telecoils are about more than telephones. The Hearing Journal, 59, 24-28.
LI Components • Microphone • Loop amplifier • Loop wire • Telecoil
Loop Inducton • Large area • Home area (cushion loop pad)
Silhouette: Near telecoil and signal relatively low therefore less susceptible to) most EMI (ElectroMagnetic Interference). Stay aligned relative to the hearing aid, they are less sensitive to head position. Neckloop: Drive both hearing aids (not with true stereo, but with a mono signal into both aids). Does not require wires running up the neck to the hearing aid(s), and can be worn under a shirt or jacket. Loop Options • Portable Loop • Portable and able to carry • Communicate one on one or in small groups, cars, etc.
Loop Induction • LI transmits via an electromagnetic field and require no receiver if the hearing aid wearer has a telecoil • Oval Window
Loop Induction: Telecoils • Inductive/audio loop systems transmit an electro- magnetic field • Receivers are not necessary for hearing aid wearers with a telecoil (the telecoil itself is the receiver) • Loop receivers can be provided for people who do not have telecoils. • Loops are often permanently installed Silhouette inductor Neckloop Direct audio input
ALDs/Hat Radio Frequency Systems
Radio Frequency • FM (radio frequency) systems transmit radio waves to receivers • Used in classrooms and where mobility is required • Not affected by light, able to cover 100+ feet, and are portable • Systems can be set to different frequencies to allow several uses in same place • Miniaturized FM receivers using the 216-217 mhz range are available as an attachment for some BTEs and CI processors • Some FM transmitters have built-in microphones that can switch from an omnidirectional, directional and/or super directional setting • Susceptible to some radio interference
Radio Frequency Systems Phonak • Multi-frequency receivers (MLxS, ML8S and ML9S) synchronized automatically using the WallPilot or directly with Campus S. The MLxS also has a standardized connector that makes it compatible with both Phonak hearing instruments and BTEs from other manufacturers • Single-frequency receivers (MLx, ML8, ML3-7) • single-frequency receiver which clips to BTE hearing aid • MicroLink CI S • miniaturized FM receiver for cochlear implant users that attaches directly to the bodyworn speech processor • WallPilot • hangs at the entrance to a room and performs an Automatic Frequency Synchronization (AFS) and ensures that the multi-frequency receivers of wearers entering the room are automatically set to the correct frequency
FM Radio Frequency Systems Phonic Ear • Sprite BTE FM • used by people of all ages who have hearing abilities ranging from normal to profound loss used in the car, at restaurants and parties, watching TV, on tours, and talking with others across a distance. • students with ADD or CAPD benefit • Toteable
BlueTooth • Bluetooth is a short-range, wireless, digital communication standard. • Bluetooth devices send data and voice in a clean, clear, digital format • audio signal is not subject to the same sources of signal degradation that sometimes compromise the quality of analog (FM, AM or inductive) transmissions. • Radio frequency transmission in the 2.4-gigaHertz range
BlueTooth Advantages • Bluetooth signal is extracted from the noise; it alone is transmitted and amplified, while noise is rejected. • Minimizes battery consumption for portable devices • Also, it places an intentional limit on the range of transmission — the most common version has a range of 10 meters which helps to avoid interference among nearby devices • Walls and other obstacles have a negligible effect on Bluetooth transmission
ALDs/HAT Infrared Systems
Infrared • Infrared systems transmit sound via infrared light waves to receivers worn by users • IR commonly used in courtrooms, movies, and live performance theaters, conventions and with TVs (signal contained in room) • Infrared systems may be susceptible to interference from bright sunlight or fluorescent lights • Requires line-of-sight between the IR transmitter and the receiver, IR waves can effectively reflect off some surfaces, depending upon the power of the transmitter
Audiovisual FM • AudiSee • Assistive device to facilitate speechreading and hearing, primarily in educational settings • Portable • Camera and microphone worn by speaker • less strain to speechread when teacher moves about the classroom or turns to write on the blackboard
Sound Field Systems • Portable or permanently installed speakers placed close to listeners at a distance from the speaker • They are most often used in classrooms and are helpful for people with mild to moderate loss • They offer a secondary benefit to those who are not HOH • Wireless speakers perform the same function. • Audio Enhancement Video 1 • Audio Enhancement Video 2