Bilateral implants distinguish sound better

Editor: Bilateral cochlear implants (CIs) are becoming increasingly common, and the consensus seems to be that they offer significantly better hearing than a single CI. That's the result most of us expected. There are good reasons for us having two ears, after all!

The following report is from the "Medical Post" in Toronto, Canada, and is reprinted with their permission.

~~~~~~~~~~~~~~~~~~~

Help children, adults pick out speech in noisy environments

By Pippa Wysong

DAYTONA BEACH, FLA. - Bilateral cochlear implants help both adults and children in picking out and hearing speech in a noisy environment. Adults can also determine from which direction sounds are coming with two implants, but children are unable to do this, researchers have found.

Generally, deaf patients have only one cochlear implant because of the price tag-about $50,000 US each, Dr. Ruth Litovsky (PhD) told the Medical Post. Dr. Litovsky is a professor of communicative disorders at the Waisman Centre at the University of Wisconsin and presented the findings at the annual meeting of the Association for Research in Otolaryngology here.

Single implants also tend to be used as a safeguard.

When an implant is placed in the ear, it likely will "obliterate the hair cells" that play an important role in hearing, she said. If a new technology or treatment became available in the future, it would not work on patients with bilateral implants.

In a study to determine the effectiveness of bilateral implants, 17 adults who had lost their hearing but who had never had cochlear implants were recruited. Each received bilateral implants at the same time.

The operation was also done on four children, ages five to 12 years. Each, however, already had a single cochlear implant.

Noise simulated cocktail party

To test for the ability to recognize speech, adults were placed in a room with several loudspeakers. Most of the speakers had noise coming out of them that simulated sounds of a cocktail party. One speaker had sentences coming out of it.

The task was to accurately repeat the sentence. Subjects did the task with one implant turned on, then with both.

"With the two implants, they could repeat the sentences accurately far better than they could with one," Dr. Litovsky said. They also were able to determine much better from which direction specific sounds came.

The children's task differed. Sitting at a computer, single words came through a speaker and the children had to select an image that matched the word-such as selecting the image of a dog if the word "dog" was said. There were other sounds that came out, too.

"Similar to the adults, the kids showed big improvements in hearing a word through competing sounds," she said.

But in localizing sounds the chlidren didn't do very well, and it didn't matter if one implant was turned on or both.

Why they didn't perform well in this latter task, even six months after the second implant was put in, remains a mystery. It could be the neural pathways needed for this task were not properly developed or had atrophied, Dr. Litovsky said.

In the adults, who all had their hearing as children, the pathways may have already been well developed. Its possible the children will improve later on, and the researchers plan to do longer-term followup.

Not cost-effective in Canada

Toronto otolaryngologist Dr. Julian Nedzelski said, "We do not implant both sides (in Canada) because of the costs involved. There is evidence to show that this is not cost-effective." He is chief of otolaryngology at Sunnybrook and Women's College Health Sciences Centre.

Evidence does suggest there could be some benefit, he said.