Transcript Hearing Aids

Hearing Aids (HA)
Or technology to the rescue
Upcoming Talk: Isabelle Peretz
Musical & Non-musical Brains
Nov. 22 @ 12 noon + Lunch
Rm 2068B South Building
Finishing up with Tinnitus
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One last method of treatment
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Tinnitus retraining therapy
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Habituation to tinnitus sound to reduce
aversiveness
HA Basics
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BTE
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ITE
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In the ear
ITC
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Behind the ear
In the canal
CIC
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Completely in canal
HA History
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Ear trumpets
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Prehistoric
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Speaking tubes (17th century)
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In-ear, around ear
Limited frequency range
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Direct sound from mouth
Aurical Aids
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Hollowed ram horns
Effective at less than 1000 Hz
Artificial ear drums (19th century)
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Perforated ear drum
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Try to insert rubber, cotton or dermal layer
Wire attachment to ossicles
Ineffective
Early Electronic HAs
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Carbon-based (early 20th century)
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Carbon microphone
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Sound  Diaphram: moves carbon globules
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Problems
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Static, no additional amplification
Bulky, large battery
Benefits
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Motion of carbon in electric field creates current
Gain 30 dB SPL
Greater frequency range (500 – 2000 Hz)
Vacuum Tube (circa 1920)
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Multiple vacuum tubes response to current in
microphone
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Problems
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Expensive, Multiple batteries, bulky
Benefits
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Powerful (up to 140 dB SPL gain)
Analogue Technology (75%
sold)
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HA: no more vacuum tubes by 1953
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Transistors introduced 1952
Transistors: Cheaper to produce, much less
energy required, equal power
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Head-mounting
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Allowed for integrated circuits
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Multiple transistors & resistors in same area
Benefits
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Eye-glass, Barrettes
Cheaper, less bulky, improved frequency range
Problems
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No signal processing
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All linear changes in amplification
HAs Design
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Microphone  Amplifier  High/Low pass
filters  Attenuators  Adder  Variable
gain amplifier  speaker (output)
Digital HAs (25%)
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Convert analogue signal to digital
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Advantages
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Much greater capacity for signal processing
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Less energy consumption
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Preprogrammed environments
Lighter
Cheaper to produce
Problems
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Programmability?
HA Effectiveness
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HOH Population 40% neutral or dissatisfied
with HA (Cochran, 2002)
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No difference between Digital & Analogue
Problems
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Battery 100 hrs (1 week to 10 days)
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Will run out, must be replaced/recharged
Limited benefit in noise
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Best if 1 meter or less