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Cochlear Implants

Cochlear Implants The cochlear implant is the most significant technical advance in the treatment of hearing impairment since the development of the hearing aid around the turn of the century. Designed to restore some sense of hearing for:.

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Cochlear Implants

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  1. Cochlear Implants The cochlear implant is the most significant technical advance in the treatment of hearing impairment since the development of the hearing aid around the turn of the century. Designed to restore some sense of hearing for: • Children or adults who receive little or no benefit from hearing aids. • Loss must be: (a) profound, (b) bilateral, and (c) sensorineural. • Problem: Auditory nerve is intact, but hair cell transducers are not functioning. Purpose of implant: Generate electrical signals that do the job of the damaged hair cells.

  2. Normal Ear Deafness: Normally functioning hair cells not present; some atrophy of 8th N fibers.

  3. Transmitting Coil Receiving Coil Electrode Array

  4. The speech processor uses a bank of bandpass filters (or a Fourier analyzer) to analyze the signal before passing it along to the array of electrodes. What part of the auditory system is the speech processor replacing?

  5. This figure shows which electrodes are receiving the most electrical current for some sample speech sounds for a 22-electrode implant. (Note that electrode 1 stimulates the basal end and electrode 22 stimulates the apical end.)

  6. 1 ch 2 ch 3 ch 4 ch 6 ch 8 ch music (orig)

  7. GOOD NEWS, BAD NEWS First the Bad News • Implant based primarily on place theory. If we make the most generous assumption that place theory is correct (it probably isn’t), how many stimulating electrodes should there be? • The CI restores some sense of hearing, but it is nowhere near the hearing sensation that is produced in a normal ear. (There are no “bionic parts” that work as well as the original.) • Subjects vary wildly in the amount of benefit they derive from a CI -- mostly for unknown reasons.

  8. Now the Good News Despite these drawbacks, CIs work. Research shows: • Ability to understand speech improves. • Children acquire speech and language skills more quickly. • Post-lingually deafened adults (the largest deaf population) maintain their speech production skills better -- especially control of pitch and loudness, which improves immediately most of the time.

  9. Addendum: How the Implant Works: The Standard Story This explanation obviously requires that 8th N dendrites be present. Are they?

  10. A postmortem study of 16 temporal bones from CI patients by Linthicum (1991)* showed that some have very few BM dendrites and most had none. How do you get tonotopic organization out of a system like this in which the full bundle of 8th cell bodies is stimulated all at once rather than in a frequency-selective way? *Linthicum FH, Fayad J, Otto SR, Galey FR, House WF (1991). "Cochlear Implant Histopathology," Am J Otol 12 No 4 1991 245-311.

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