"For most cochlear implant users with significant residual hearing in the non-implanted ear, there are auditory advantages to using a hearing aid in conjunction with the implant."
Cochlear implants have come a long way in recent years. Speech processing strategies continue to be introduced and refined; new types of electrode arrays and insertion techniques provide more efficient electrical coupling with nerve endings; fitting techniques (mappingl have been improved and standardized; while circuit miniaturization permits advanced technology to be incorporated in a behind-the-ear case. It is the implications of this latter development, coupled with a relaxation of candidacy criteria that I would like to comment here.
When implants were first introduced, FDA criteria for candidacy were extremely rigid. Essentially, a person had to be profoundly deaf and obtain basically no benefit from hearing aids. These were the days when the presumed benefits of cochlear implants focused on its contribution to speechreading, the detection of alerting and warning sounds, and its role in helping people monitor their own vocal outputs. While all these are desirable, these are relatively low-level auditory functions (as opposed to the auditory recognition of speech).
However, from the time implants were introduced, they have had the benefit of well-controlled, longitudinal clinical research. The merits of each new development or device were accompanied by such research, conducted by the most sophisticated of researchers. What this research has shown is that an average person's performance with cochlear implants has dramatically improved over the years. This, in turn, has led to a relaxation of the audiological candidacy criterion for a cochlear implant. Now people with severe hearing losses, with sentence identification of up to 50 percent in the ear to be implanted are considered candidates Land no more than 60 percent binaurally).
In other words, people who have usable residual hearing, who are able to substantially benefit from hearing aid usage, are now implant candidates. The rationale underlying this relaxation of candidacy is that post-implant, the listening performance of the average implantee is much higher than the candidacy criterion of 50 percent, being in the neighborhood of about 90 percent. (I should point out here that this criterion specifies sentence identification" and not monosyllabic words, which is a much more difficult listening task.) But given the presence of usable residual hearing in the non-implanted ear (since it is the worst ear that would usually be implanted), has raised the question of whether it would be beneficial for implant users to wear a hearing aid in the non-implanted ear. At least three studies have been conducted on this topic.
The consensus of these studies is that, for most cochlear implant users with significant residual hearing in the non-implanted ear, there are auditory advantages to using a hearing aid in conjunction with the implant. When children were the subjects, the results showed significant benefits in speech perception, localization, and aural/oral functioning.
These investigators stress the fact that the hearing aid in the non-implanted ear still needs careful fitting and that this can make a difference. Other investigators report that while there may be a complex pattern of loudness differences between the implanted and hearing aid aided ears, a substantial amount of loudness summation was still observed for the binaural stimuli. This suggests binaural integration of the sounds from the two ears in the higher auditory pathways, with some indications of improved localization and speech perception.
What I would conclude from these studies is that it is worth trying a hearing aid in a non-implanted ear, given some degree of usable residual hearing in that ear. If such a trial doesn't work out, it's no problem to take out the hearing aid.
The advent of behind-the-ear cochlear implants has also led to a related question; i.e., how does auditory functioning with bilateral cochlear implants compare to a single implant? From the point of view of possible candidates, we can imagine that they would think long and hard before undergoing another cochlear implant procedure. It would not be an easy decision to make; and the more research that is done on the topic, the easier such a decision would be.
Several studies at the University of Iowa and one conducted in Germany have investigated the possible merits of bilateral implants. In the German study, nine subjects were tested in quiet and noise under three conditions: with both implants and with (ust the right or left implants. In the unilateral condition, the noise was either on the same side as the implant or on the opposite side.
The investigators report that all the subjects benefited from the bilateral stimulation in all conditions. And as we would expect, in the unilateral condition, the subjects did better when the noise came from the side opposite to the implant. This study did not include tests for localization.
Essentially, the same type of study was conducted at the University of Iowa, but with the addition of localization tasks. Insofar as the localization tasks were concerned, for their nine subjects they found 'generally" better skills with two implants than with one. Results on the speech perception tasks were more variable (though none showed a decrement in binaural compared to monaurali.
The advantages of bilateral implants were most apparent when the noise emanated from the side opposite to the implant with the speech coming from the frontr This is because the head blocks some of the background sounds from entering the implant microphone.
Actually, these same results have been found with binaural hearing aids as well. In other words, with any kind of binaural system, in addition to the possible binaural integration effect, there will always be one ear more favorably oriented to the source of the speech signal.
It should be noted that binaural implants and binaural hearing aids do not necessarily provide the same auditory benefits. We know that binaural hearing aids, generally speaking, offers listening advantages superior to those with a monaural hearing aid. On average. there appears to be similar advantages to binaural cochlear implants as well, but this would not be predictable from the hearing aid
From Hearing Loss, May/June, 2003.
Acknowledgement: This column is supported, in part, by GRANT #133E980010 from the U.S. Department of Education, NIDRR, to the Lexington Center.
Mention of products or companies by the author does not Indicate SHHH endorsement, nor should exclusion suggest disapproval. Since everyone's communication problems and needs vary, SHHH suggests consulting with your hearing health professional.