Amplification systems: Hearing aidsAmplification systems: Hearing aids

May be analog or digitalMay be analog or digital

Consists of a microphone, amplifier, and loudspeaker.Consists of a microphone, amplifier, and loudspeaker.

Earlier: Linear. Now, compressive with automatic gain Earlier: Linear. Now, compressive with automatic gain controlcontrol

Directional microphonesDirectional microphones

Different types of hearing aids: Body level, BTE, ITE, Different types of hearing aids: Body level, BTE, ITE, ITC, CIC, Bone-conduction, Eyeglass, disposable, ITC, CIC, Bone-conduction, Eyeglass, disposable, CROS.CROS.http://www.nidcd.nih.gov/health/hearing/hearingaid.htm#4

http://www.ahaanet.com/hearingaidstyles.asp

Hearing aid characteristicsHearing aid characteristics

OSPLOSPL Gain: Gain:

Full on gain versus reference test gainFull on gain versus reference test gain Functional gain versus insertion gainFunctional gain versus insertion gain

Frequency responseFrequency response DistortionDistortion Battery drain, equivalent input noise levelBattery drain, equivalent input noise level

ImplantsImplants Bone-conduction implants Bone-conduction implants http://

products.cochlearamericas.com/baha/introduction-to-baha-baha-and-natural-hearing

Middle ear implants Middle ear implants http://www.hearingcenteronline.com/newsletter/august00c.shtml

Auditory brainstem implants Auditory brainstem implants http://www.earinstitute.org/news/facts/abifact.htm

Cochlear implantsCochlear implants

Direct stimulation of the auditory nerveDirect stimulation of the auditory nerve

http://www.nidcd.nih.gov/health/hearing/coch.asp http://www.nidcd.nih.gov/health/hearing/coch.asp

http://www.mayoclinic.com/health/medical/IM02586 http://www.mayoclinic.com/health/medical/IM02586

Consists of external and internal units.Consists of external and internal units.

External: External: MicrophoneMicrophone that picks up acoustic signals, converts that picks up acoustic signals, converts it to electrical signals and feeds it to a it to electrical signals and feeds it to a speech processorspeech processor. . Speech processor then delivers these coded signals to a Speech processor then delivers these coded signals to a transmittertransmitter, which converts it to magnetic impulses, which converts it to magnetic impulses

Internal: Internal: ReceiverReceiver and and electrode arrayelectrode array..

Candidacy issues: Age, hearing lossCandidacy issues: Age, hearing loss

Cochlear implantCochlear implant

Issues in amplificationIssues in amplification

Candidacy: Should depend on individual’s specific Candidacy: Should depend on individual’s specific needs.needs.

Goal of amplification: To restore sensitivity, clarity (in Goal of amplification: To restore sensitivity, clarity (in quiet and noise) and to prevent amplification to quiet and noise) and to prevent amplification to intolerable levels.intolerable levels.

Earlier: Comparative methodsEarlier: Comparative methods

Now: Prescriptive methodsNow: Prescriptive methods

Verification of hearing aid performance very important. Verification of hearing aid performance very important. Compensate for insertion loss. Real ear measures.Compensate for insertion loss. Real ear measures.

Assistive listening devicesAssistive listening devices

Allows the signal to be closer to the Allows the signal to be closer to the amplification system.amplification system.

Interface can be FM, infrared, or Interface can be FM, infrared, or electromagnetic coupling .electromagnetic coupling .

Other types: For awareness. Example: Other types: For awareness. Example: Visual or vibrotactile devices.Visual or vibrotactile devices.