Transcript Amplification/Sensory Systems

Amplification/Sensory Systems
SPA 4302
Summer 2006
Hearing Aid Development
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thru the 1800s: Acoustic Devices
Circa 1900: Carbon Devices
1930s: Vacuum Tube Devices
1950s: Transistor Devices
1980s: Digital Devices
Hearing Aid Circuit Overview
• Analog:
– mic – amp – filters – atten – receiver
• Digital:
digital
– mic – AtoD – processing – DtoA – receiver
• Compression: circuitry or programming to
reduce the amplification of loud
sounds to keep them below UCL
• Tele-coil: direct pick up from a
telephone’s electromagnetic field
Characteristics of Hearing Aids
• OSPL:
– Maximum output of aid
• Acoustic Gain:
– dB difference between output and input
• Frequency Response:
– range of frequencies amplified
– shown as curve, and calculated
• Distortion:
– equivalent input noise
– harmonic distortion
Binaural Amplification
• Monaural fittings may permit auditory
deprivation effects in the unaided ear
• Binaurally fitted pts may show improved
– listening in noise
– localization
• HOWEVER,
– this has been difficult to document clinically
– some (particularly elderly) pts will actually do
worse with binaural than monaural fitting.
Types of Hearing Aids
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Digital/Analog/Hybrid
Behind the Ear
In the Ear
Canal
Completely in Canal
Bone conduction
Implanted
Cochlear
Implants
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Mic - Processor - electrodes
Electrical stim of neurons
via up to 22 electrodes
Latest generation of devices
are successful with both postand pre-lingually deafened
pts.
Selecting Hearing Aid Candidates
• More than just the audiogram:
• Expectations and Motivation
• Communicative Demands
• Vocation/Education/Financial Resources
Dispensing Hearing Aids
• An Historical/Hysterical Issue:
• Audiologists are the persons best qualified
to fit hearing aids.
Selecting HAs for Adults
• Ideal HA fitting should (Carhart, 1975):
– Provide a restoration of adequate sensitivity for speech
and environmental sounds too faint to hear without the
hearing aids
– Provide a restoration, retention, and or acquisition of
the clarity (including intelligibility and recognition) of
speech and other sounds within ordinary, relatively
quiet environments
– Achieve the same when these sounds are in noisier
environments
– Ensure that higher intensity sounds are not amplified to
an intolerable level
Verifying Hearing Aid Performance
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Probe microphone “Real Ear” measurements
With hearing aid in place (in situ)
Without aid in (real ear unaided response)
Insertion loss: presence of aid in ear plugs it
and alters the resonance of the pinna and canal.
Hearing Assistance Technologies
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Assistive Listening Devices
Visual/Vibratory Alerting
FM/Infrared transmission
Telephony