Although cochlear implants (CI) and hearing aids (HA) serve the same purpose there are differences between them. Hearing aids deliver amplifed sound to the damaged cochlea. Depending on the type of loss, be it the common-ski slope shaped hearing chart (high frequencies are most severely impacted) or reverse-slope loss (low frequencies are impacted), a hearing aid can be programmed to shape the amplification of sound to match the loss. Sound is still being delivered to damaged nerves, so HAs are limited in ability to aid severe and profound loss beyond environmental sounds and vowels in speech. The use of a hearing aid at the severe and profound level can be deceptive in the perceived benefit due to the fact you “can still hear.”
Modern hearing aids can do lots of processing, including compensating for hearing loss that varies at different frequencies, and improving performance in noise. But in the end, they can only present the sound to you by yelling in your ear. The signal is still processed by the damaged cochlea and sent to the brain with its added distortion. Even with substantial amplification, you may not hear very much, and you become tired and strained due to the loud sounds being presented to your ear.
Cochlear implants operate very differently than hearing aids. A cochlear implant bypasses the damaged hair cells by delivering electrical current directly to the cochlear, or auditory, nerve. A cochlear implant presents a wide range of frequencies, regardless of the pre-implantation hearing loss.
The primary benefit of a hearing aid over a cochlear implant is in the area of low frequencies. Low frequencies are detected at the apex (inner-most area) of the cochlea. Current implant technology limits the insertion depth of the electrode into the cochlea, limiting access to the lower frequencies below 250 Hz. Those who are able to use a hearing aid in one ear and an implant in the other are encouraged to do so for this reason. Users who rely solely on an implant to hear generally find that they gain access to/perceive low frequencies via harmonics once the brain has learned to translate the electrode signal.
People who transition from HAs to CIs generally find that compensation techniques such as lip-reading become easier. Eventually, you may reach the point where you require very little compensation.
With hearing aids, many people try to increase the volume as much as possible. With a severe or profound hearing loss, this may provide some cues to aid in reading lips and interpolating contextual cues. Cochlear implants provide plenty of sound, so that you don’t need to have high volumes blasted into your ear just to get those sounds. Your job is to learn how to interpret them so that it becomes second nature.
Many types of hearing loss involve more loss at high frequencies. This is particularly unfortunate because much of the important information in speech resides in those high frequencies. Hard consonants and sibilant sounds all have a lot of high-frequency content. If you don’t hear at those frequencies, it sounds like everybody mumbles unintelligibly.
Hearing aids, especially those fit for severe and profound loss, are prone to feedback (whistling.) Eating, talking, and chewing gum all affect hearing due to the loosening/tightening of the ear canal around the ear mold. Cochlear implant users do not experience either issue. No ear mold or amplified sound is involved in the process. The lack of an ear mold is a comfort bonus as well.
Advantages of Cochlear Implants:
- Eliminates earmolds, their acoustic feedback issues and irritation of the ear bowl
- Can enable you to hear conversation and thus learn spoken language with relative ease, particularly for those with severe-profound hearing loss
- May enable you to use a regular telephone
- Easier high- frequency speech component perception ( /sh/, /s/, /f/, /t/, /k/, /p/, /h/)
- Better overall hearing at high frequencies
- Distance hearing is likely better than with hearing aids
- May enable you to overhear conversations and other environmental sounds
- Better feedback which may help improve your voice quality
- May be the only option when a hearing aid is insufficient.
- May help with auditory neuropathy
Advantages of Hearing Aids:
- It is easy to try different hearing aids to see which works best for you
- You can take advantage of new technology as it becomes available (improved earmolds, tubing, telecoils, digital/analog programming strategies)
- Retain residual hearing for possible future technology or medical improvements
- May provide better low frequency sounds, such as those in vowels.
- Does not require surgery
Sam Spritzer and David Ryan, with excerpts from www.AuditoryVerbalTraining.com (currently unavailable) used with permission. Credit is given to the author of the website, Ellen A. Rhoades, Ed. S., Cert. AVT.