1. Amplification/Sensory Systems SPA 4302 Summer 2007

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 AnalogAnalog: –mic – amp – filters – atten – receiver DigitalDigital: –mic – AtoD – processing – DtoA – receiver CompressionCompression: circuitry or programming to reduce the amplification of loud sounds to keep them below UCL Tele-coilTele-coil: direct pick up from a telephone’s electromagnetic field digital

4. Characteristics of Hearing Aids ________-: –Maximum output of aid Acoustic Gain: –dB difference between output and input __________________-: –range of frequencies amplified –shown as curve, and calculated Distortion: –equivalent input noise –__________ distortion

5. Binaural Amplification auditory deprivationMonaural 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 ____- Processor - electrodes Electrical stim of neurons via up to ___ 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 in situWith hearing aid in place (in situ) real ear unaided responseWithout aid in (real ear unaided response) Insertion lossInsertion loss: presence of aid in ear plugs it and alters the resonance of the pinna and canal.

12. Hearing Assistance Technologies _________________________ Visual/Vibratory Alerting FM/Infrared transmission _________________