Posts tagged deafness

Portrait of a mature man, possibly with single-sided deafness, giving his ear against a white background

Getting to Know Single-Sided Deafness

Portrait of a mature man, possibly with single-sided deafness, giving his ear against a white background

One of the most serious issues presented by single-sided deafness is the loss of spatial hearing.

Single-sided deafness, or SSD, is a condition in which a person has good hearing in one ear, and non-functional hearing in the other ear. By ‘non-functional hearing’, it is meant that even with the help of some system of sound amplification, the bad ear cannot be made functional again. The most common reason for this is that a person with SSD has sustained damage to the inner ear, so amplification has no effect whatsoever on hearing ability in that ear.

Problems Presented by SSD

One of the most serious issues presented by single-sided deafness is the loss of spatial hearing. Spatial hearing allows a person to identify sounds both distant and nearby, in addition to all those that occur within 360° of the head area. Because our two-tiered auditory system is oriented to evaluate very specific information that can localize and pinpoint sounds, there is a big loss sustained when one ear is completely subtracted from that model.

It creates some difficulties for the brain, in terms of evaluating the information it receives and trying to assess what kind of information is missing. When the non-functional ear is in the acoustic shadow of the functional ear on the other side of the head, there can be significant difficulty with interpreting speech and other sounds, versus normal background noises.

This is especially true when speech or other distinctive sounds reach the non-functional ear first, and are not really ‘heard’ until the sound signal travels around to the other side of the head, to be received by the good ear. The net effects of this kind of sound reception are: a serious degradation in listening quality, difficulty with the interpretation of sounds and speech, and in a broader context, lowering of a person’s quality of life.

Another of the difficulties with single-sided deafness, alluded to above, is the condition known as ‘head shadow’ effect. What is meant by head shadow effect is a situation where sounds originating on the side of the head where the non-functioning ear is, are actually obstructed by the head itself in traveling to the other side of the head where the good ear is.

The main problem with this is that some kinds of sounds become very difficult to hear with the good ear. Low-frequency sounds are mostly unaffected in this scenario, because they have a long wavelength and they can move around the head more readily to the good ear. High-frequency sounds on the other hand, are characterized by much shorter wavelengths, and many of these are typically reflected by the head, and become altered before they reach the good ear.

Since consonant sounds occur largely in the high-frequency wavelengths, this can have a big impact on communication, because it is much more difficult to differentiate those sounds from background noises. Therefore, the biggest impact of this head shadow effect is on communication, and it causes a person with SSD to miss a great deal of what may have been said by someone, even if they’re standing close by.

Causes of SSD

One of the more common causes of single-sided deafness occurs is when surgery is necessary to remove a tumor growing in the ear. This kind of surgical removal sometimes causes such damage to the auditory nerve that a patient loses most or all hearing in that ear. If such tumors are not removed, they will continue to grow slowly, and will eventually cause damage to the ear anyway, including possible loss of hearing. However, surgical treatment can end up being just as harmful, if the auditory nerve becomes damaged.

A secondary cause of SSD is known as sudden idiopathic hearing loss, which is generally attributable to some kind of viral infection. In this scenario, a virus infects the cochlea, which eventually leads to swelling and permanent damage to the delicate structure of the cochlea. It happens fairly frequently that the ear cannot recover from this kind of damage, and the person is left with no hearing in that ear.

A third cause for SSD stems from some kind of blunt trauma to the head. In such cases, there can be a transverse fracture of the critical temporal bone, which has the effect of rendering the cochlea non-functional from that point forward. It is also possible for people to be born with hearing loss in one ear, while having perfectly good hearing in the other ear.

Solutions for SSD

One of the most effective solutions for SSD is known as a Contralateral Routing of Signal (CROS) configuration, in which a microphone is placed in the non-functioning ear, and transmits received sound signals over to a receptor in the good ear. The first of these configurations relied on a tiny wiring system for the transmission of sound between ears, but this has now been improved and refined with a wireless system that makes the whole arrangement less bulky and more effective.

There are now also two additional high-tech solutions which build upon the idea that sound received on the non-functioning side is somehow transported to the good side so that relatively normal hearing is possible. These two processes are known as bone conduction solutions and bone anchored solutions.

In the first, sound is actually transmitted through the bone of the skull to the other side of the head, and in the second, sound is transmitted by a subcutaneous implant which transmits sound through the skin to the good ear. As you might expect, these solutions can be relatively costly, but they can also be a very effective means of restoring normal hearing to someone who has completely lost hearing in one ear.

A hearing aid on a white background.

The Benefits of a Hearing Aid

A hearing aid on a white background.

How well does a hearing aid work?

It’s amazing how technological advancements have made life better for so many people, especially in the world of medicine. Scientists often research this type of technology to see how well they work. With this research, they access the technology’s effectiveness and make improvements. Recently, researchers looked into the hearing aid, hoping to find out if it had lasting effects.

The Purpose of a Hearing Aid

It is common for older adults to lose their hearing. That is why hearing aids were created. They are a solution to a problem that affects plenty of adults. Sounds become louder, speech skills increase, and cognitive understanding improves.

Many who need this hearing technology do not use it. In fact, less than 30 percent of adults over 70 years old use hearing aids. If you expand the age range from 20 to 69, only 16 percent of people who need hearing aids use them.

Testing Different Hearing Aids

The objective of the research was to prove that hearing aids do provide a benefit, no matter what kind. There are generally two types of hearing aids that people buy. The first is customized and created after a consultation with a doctor. The other is cheaper, pre-programmed hearing aid.

Scientists gathered 154 adults, ages 55-79, with hearing loss. They separated them into three groups:

  • Customized group
  • Pre-programmed group
  • Placebo group

People in the placebo group were given aids that provided no hearing benefits. After testing, they found that both the customized and pre-programmed hearing aids were effective. However, people in the customized group were more likely to buy their hearing aids.

Overall, people liked the quality of the customized hearing aid better. When offered the customized hearing aid, the pre-programmed and placebo group were more impressed by its quality. Hopefully, patients with hearing loss will see that hearing aids help, no matter what kind.

An X-Ray of a Human brain with parts like the auditory cortex highlighted in several colors.

Auditory Cortex Is Identical in Deaf and Hearing People

An X-Ray of a Human brain with parts like the auditory cortex highlighted in several colors.

Scientists discover new information about the auditory cortex and the role it plays in hearing.

According to the National Institute on Deafness and Other Communication Disorders, nearly 10 percent (25 million people) of the United States population has experienced tinnitus lasting at least five minutes. Approximately 15 percent (26 million people) of Americans, between the ages of 20 and 69, have hearing loss due to exposure to loud noises.

Scientists continue to search for answers to how hearing loss affects the body. A recent study has made an interesting discovery about the auditory cortex—which is the part of the brain that processes sound.

Revealing Details About the Auditory Cortex

Researchers at several institutions, including Harvard University, sought to better understand how the auditory cortex works. Using tonotopic maps (images of the brain), the scientists were able to analyze how this part of the brain reacts to different tones. They discovered that for both the hearing impaired and those with normal hearing, the neural architecture in the auditory cortex is identical.

“One reason this is interesting is because we don’t know what causes the brain to organize the way it does,” said Striem-Amit, the lead author of the study. “How important is each person’s experience for their brain development? In audition, a lot is known about (how it works) in hearing people, and in animals…but we don’t know whether the same organization is retained in congenitally deaf people.”

The result of the study raises a lot of questions. In their test, the auditory cortex reacted to not only sound but visual stimulation. “We know the architecture is in place—does it serve a function?” Striem-Amit said. “We know, for example, that the auditory cortex of the deaf is also active when they view sign language and other visual information. The question is: What do these regions do in the deaf? Are they actually processing something similar to what they process in hearing people, only through vision?”

More research needs to be done. While the auditory cortex seems to develop in a similar manner, whether or not the person is deaf, some suggest it still might play a vital role in hearing.

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