|By Cheryl Heppner, 8/10/11
Dr. Matthew Bakke, director of the Rehabilitation Engineering Research Center (RERC) on Hearing Enhancement and Professor and Chair of the Department of Hearing, Speech and Language Sciences at Gallaudet University was joined by his colleagues at Gallaudet to present on their research findings. Their work addresses the communication needs of people with hearing loss and provides recommendations for enabling them to have effective communication access.
Dr. Bakke first touched on the topic of listener factors that affect communication access, noting that among deaf and hard of hearing individuals there is a great diversity in the degree of hearing loss, its type, configuration, laterality, and symmetry.
Degree of Hearing Loss
Speech heard by an individual with moderate hearing loss of 30 to 60 decibel threshold is likely to be only partly audible. Although hearing aids can restore full audibility, they have increased susceptibility to interference.
For an individual with severe hearing loss of 60 to 90 decibel threshold, there is no audibility of speech without hearing aids, and hearing aids can provide full audibility but auditory clarity can range from good to poor.
With profound hearing loss of higher than 90 decibels, an individual will have only partial audibility of speech with hearing aids and little speech discrimination without visual cues such as those from speechreading, or use of sign language, captioning, or cued speech.
Hearing acuity also can vary depending on the type of hearing loss – sensory, neural, or conductive – and whether it is in one or both ears.
Auditory Processing Ability Factors
Frequency Resolution – discriminating sounds of different pitch in speech, such as consonants (b, t, d, s, etc.) and vowels (a, e, i, o, u).
Amplification Resolution – discriminating the dynamic changes in the level of the speech signal, or volume.
Temporal Resolution – Discriminating the rapidly changing speed patterns of speech
Binaural Factors – using two ears vs. using one ear.
Use of hearing aids gives a range of speech audibility from full to very limited. Hearing aids can provide an increase in amplification (gain) and the amplification can vary across the frequency of sound, improving speech audibility. What hearing aids cannot do is provide improved auditory resolution.
Microphones worn on the head are susceptible to noise and reverberation. While noise reduction technologies are available to address this, they are limited in how much they can help.
The use of cochlear implants by individuals with severe to profound hearing loss has been increasing, and this technology makes full audibility of speech possible. However, auditory resolution ranges from poor to good, and as with hearing aids, head-worn microphones are susceptible to interference. Individuals using cochlear implants have a wide range of outcomes and some may depend on visual cues such as speechreading, sign language or captioning.
Coupling Hearing Aids and Cochlear Implants
There are several options to improve audio quality to hearing aids and cochlear implants. One is Direct Audio Input (DAI) which is offered by for some manufacturers for select models. There is no universal DAI connection that will work with all hearing aids or cochlear implants.
Another option is the use of a telecoil and neckloop or silhouette. These are considered low technology with high yield, but only if the hearing aid or cochlear implant has a telecoil that is programmed effectively for its use.
Bluetooth and other emerging wireless technologies are now finding their way into hearing aids. For some individuals the drawback with these technologies as opposed to the ease of using a telecoil is that there is more to lug around and the technologies are more complex.
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