1. Amplification/Sensory Systems SPA 4302 Summer 2006

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

3. Hearing Aid Circuit Overview • Analog: • mic – amp – filters – atten – receiver • 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 digital

4. 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

5. 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.

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

7. Cochlear Implants • Mic - Processor - electrodes • Electrical stim of neurons • via up to 22 electrodes • Latest generation of devices are successful with both post-and pre-lingually deafened pts.

8. Selecting Hearing Aid Candidates • More than just the audiogram: • Expectations and Motivation • Communicative Demands • Vocation/Education/Financial Resources

9. Dispensing Hearing Aids • An Historical/Hysterical Issue: • Audiologists are the persons best qualified to fit hearing aids.

10. 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

11. Verifying Hearing Aid Performance • 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.

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