AmplificationSensory Systems SPA 4302 Summer 2006 Hearing Aid

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Amplification/Sensory Systems SPA 4302 Summer 2006

Amplification/Sensory Systems SPA 4302 Summer 2006

Hearing Aid Development • • • thru the 1800 s: Acoustic Devices Circa 1900:

Hearing Aid Development • • • thru the 1800 s: Acoustic Devices Circa 1900: Carbon Devices 1930 s: Vacuum Tube Devices 1950 s: Transistor Devices 1980 s: Digital Devices

Hearing Aid Circuit Overview • Analog: Analog – mic – amp – filters –

Hearing Aid Circuit Overview • Analog: Analog – mic – amp – filters – atten – receiver • Digital: Digital digital – mic – Ato. D – processing – Dto. A – receiver • Compression: Compression circuitry or programming to reduce the amplification of loud sounds to keep them below UCL • Tele-coil: Tele-coil direct pick up from a telephone’s electromagnetic field

Characteristics of Hearing Aids • OSPL: – Maximum output of aid • Acoustic Gain:

Characteristics of Hearing Aids • OSPL: – Maximum output of aid • Acoustic Gain: – d. B 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

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 • • Digital/Analog/Hybrid Behind the Ear In the Ear Canal

Types of Hearing Aids • • Digital/Analog/Hybrid Behind the Ear In the Ear Canal Completely in Canal Bone conduction Implanted

Cochlear Implants • • Mic - Processor - electrodes Electrical stim of neurons via

Cochlear Implants • • 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

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

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

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 • • Probe microphone “Real Ear” measurements With hearing aid

Verifying Hearing Aid Performance • • Probe microphone “Real Ear” measurements With hearing aid in place (in situ) situ Without aid in (real ear unaided response) response Insertion loss: loss presence of aid in ear plugs it and alters the resonance of the pinna and canal.

Hearing Assistance Technologies • • Assistive Listening Devices Visual/Vibratory Alerting FM/Infrared transmission Telephony

Hearing Assistance Technologies • • Assistive Listening Devices Visual/Vibratory Alerting FM/Infrared transmission Telephony