Amplification systems: Hearing aids May be analog or digital May 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 control Earlier: Linear. Now, compressive with automatic gain control Directional microphones Directional microphones Different types of hearing aids: Body level, BTE, ITE, ITC, CIC, Bone-conduction, Eyeglass, disposable, CROS. Different types of hearing aids: Body level, BTE, ITE, ITC, CIC, Bone-conduction, Eyeglass, disposable, CROS.

Hearing aid characteristics OSPL OSPL Gain: Gain: Full on gain versus reference test gain Full on gain versus reference test gain Functional gain versus insertion gain Functional gain versus insertion gain Frequency response Frequency response Distortion Distortion Battery drain, equivalent input noise level Battery drain, equivalent input noise level

Implants Bone-conduction implants Bone-conduction implants Middle ear implants Middle ear implants Auditory brainstem implants Auditory brainstem implants

Cochlear implants Direct stimulation of the auditory nerve Consists of external and internal units. Consists of external and internal units. External: Microphone that picks up acoustic signals, converts it to electrical signals and feeds it to a speech processor. Speech processor then delivers these coded signals to a transmitter, which converts it to magnetic impulses External: Microphone that picks up acoustic signals, converts it to electrical signals and feeds it to a speech processor. Speech processor then delivers these coded signals to a transmitter, which converts it to magnetic impulses Internal: Receiver and electrode array. Internal: Receiver and electrode array. Candidacy issues: Age, hearing loss

Cochlear implant

Issues in amplification Candidacy: Should depend on individual’s specific needs. Candidacy: Should depend on individual’s specific needs. Goal of amplification: To restore sensitivity, clarity (in quiet and noise) and to prevent amplification to intolerable levels. Goal of amplification: To restore sensitivity, clarity (in quiet and noise) and to prevent amplification to intolerable levels. Earlier: Comparative methods Earlier: Comparative methods Now: Prescriptive methods Now: Prescriptive methods Verification of hearing aid performance very important. Compensate for insertion loss. Real ear measures. Verification of hearing aid performance very important. Compensate for insertion loss. Real ear measures.

Assistive listening devices Allows the signal to be closer to the amplification system. Allows the signal to be closer to the amplification system. Interface can be FM, infrared, or electromagnetic coupling. Interface can be FM, infrared, or electromagnetic coupling. Other types: For awareness. Example: Visual or vibrotactile devices. Other types: For awareness. Example: Visual or vibrotactile devices.