Intro to Audiometry 1 (College of Dupage) Flashcards
From textbook: Introduction to Audiology by Frederick Martin (37 cards)
What is the limitation of hearing aids?
Relies on integrity of hair cells, the more severe the hearing loss, the less effective a hearing aid will be. And amplified sounds can lead to distortion.
What are bone-conduction devices?
stimulate the cochlea directly (by bypassing the middle ear). sound is conducted through the base of the skull by oscillating the temporal bone.
Middle ear devices drive…
the ossicular chain directly
A cochlear implant attempts to…
restore useful hearing to severely hearing-impaired individuals. What it is… it’s a sophisticated implantable device and how it works is that it stimulates the auditory nerve directly by using electrical current.
Explain auditory function in pts with significant SNHL.
- Cochlear outer hair cells (which are the sensory receptors for audition) are damaged or significantly reduced in number
- Some surviving auditory nerve fibers within the modiolus
- Damaged hair cells are unable to transmit electrical impulses to the surviving nerve fibers
- Auditory perception severely distorted or not possible
In the United States, _____ out of every 1,000 children are born deaf or hard-of-hearing.
3
Prior to ______, the primary medical device for profoundly deaf or severely hearing-impaired children and adults was the behind-the-ear (BTE) analog hearing aid.
1975
What is the goal of cochlear implants?
Acoustic input -> convert to electrical signal -> interpreted by brain as sound
Send signals via the auditory nerve to the brain (by electrically stimulating the surviving nerve fibers in the cochlea)
Sounds are distinguished by what 3 dimensions?
- Amplitude (intensity)
- Frequency (spectral)
- Time (temporal)
Cochlear implants must account for what three characteristics in sound coding designs?
- Frequency conveyed by -> place in the cochlea that is stimulated
- Amplitude is encoded by -> current level
- Temporal cues extracted from input and are conveyed by -> stimulation rate and pattern of stimulation
What are the primary benefits of CIs?
Increased auditory perception (environmental sounds and speech)
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What are the secondary benefits of CIs?
- enhancement of lipreading skills
- enhancement of other speech perception skills (ie. discrimination, identification, recognition, and/or comprehension
- after training and experience with device, many children (and adults) demonstrate improvements in speech production and voice quality
What are the possible limitations of CI?
- Lifelong commitment! Appointments, follow up
- Everyday considerations and precautions with device use (MRI compatibility, device maintenance- charging batteries, equipment malfunction, etc)
- Small risk of side effects (surgical and medical)
- High cost/insurance limitations
- Very small risk of implant failure (as with any implantable device)
- Potential loss of residual hearing and remaining natural sound quality
- Difficulty with identification of music
In 1800, who directed electrical current across his own ears by applying two metal probes connected to a 50-volt circuit? Created auditory sensation “like a thick boiling soup”
Alessandro Volta
1930 Ernest Wever (Princeton University psychology professor) and Charles Bray (Johns Hopkins otology fellow) discovered the cochlear microphonic. How did they do this?
- Inserted electrode into auditory nerve of a cat
- Sounds made in the test room with the cat were reproduced in electrical recordings in a different room (using a telephone receiver), lead to idea of biological microphonic property
- idea emerged that cochlear hair cells convert sound into an electrical analog signal that mirrors the wave form of the acoustic stimulus
Dr. House implants the first two American patients for short-term clinical trials.
Implanted with a gold wire electrode inserted through the round window and brought through the skin. Resulted in local infections of the skin and devices had to be removed patients had sensation of hearing but no speech understanding and loudness discomfort. What year was that?
1961
Food and Drug Administration begins to regulate cochlear implants and the NIH began to fund efforts related to cochlear implantation. What year was this?
1980
Multichannel cochlear implant was approved by the FDA for use in adults in _______ (approval for children as young as two years came about five years later)
1984
Explain Single-channel CI.
Provides direct electrical stimulation to one point of contact in the cochlea using one electrode; all sound frequencies are transmitted as a single signal to the inner ear.
What are the benefits of single-channel CIs?
- Inexpensive to manufacture
- Do not require much hardware
- Conveys temporal information fairly adequately
- Restricts amount of spectral information to below 1000 Hz
- With single channel devices, patients:
- were more aware of environmental sounds (such as sirens)
- Were able to distinguish between a voiced and unvoiced sound
- Were able to identify prosodic cues (i.e. if sentence is a statement or question)
- Improved speech lip-reading skills - Limited performance! Commonly cited performance measures: ~0-4% monosyllabic word recognition
What is a multi-channel device?
- Provides direct electrical stimulation to multiple points of contact in the cochlea using multiple electrodes
- Different electrodes are stimulated depending on stimulus frequency
- Auditory neurons that are in the area of the stimulated electrode are stimulated and then send neural impulses to the brain
- Electrodes near basal end of cochlea—stimulated by high frequencies
- Electrodes near apical end of cochlear—stimulated by low frequencies
What is the optimal number of electrodes for best speech understanding?
6-8 electrodes
What are the external parts of cochlear implants?
- microphone: on external processor: picks
up sound from environment, transduces the sound to
an electrical signal, sends signal to sound
processor - sound processor: sound goes from pre-amplifier to
processor, where sound is analyzed and converted to a digital signal
Signal is then classified in terms of frequency, amplitude, and temporal domains
Signal is then converted from a digital signal back to an electrical signal - transmitter cable: electromagnetic radio frequency (RF) coil: send electromagnetic signal through the skin to the receiver under the skin
What are the internal parts of the cochlear implants?
- Receiver coil: converts electromagnetic signal to digital code/electric pulses, which are then sent to the electrode array
- Magnet: are located in the center of the external coil and internal coil, adheres the external RF coil to the head and directly over the internal coil
The RF signal serves as the power supply for the internal stimulator - Electrode array: stimulate the auditory nerve directly, which then sends signal to brain where it is perceived as sound
