Getting to Know Single-Sided Deafness
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.