Difficulties From Unilateral Hearing Loss, Explained
Unilateral hearing loss — alternatively known as single-sided deafness (SSD) — is a common occurrence for people of all ages and lifestyles. This condition involves the partial or complete loss of hearing in one ear, with lesser or no loss in the other ear.
Thousands of people report developing this disease every year, and it can have a severe disabling impact on peoples' work and social lives.
Common causes of unilateral hearing loss include:
- Bacterial infections in the ear canal
- Head injury, especially on the side of the head
- Problems with blood supply to the ear or brain
- Meniere’s disease
- Viral infections like herpes
- Tumors on the acoustic or 8th nerve
- Acoustic trauma from sudden loud noises
Difficulties From Unilateral Hearing Loss
Unilateral hearing loss may seem like a minor issue, especially when compared to complete hearing loss. However, unilateral hearing loss can still have a significant impact. People might operate well enough in quiet environments or one-on-one conversations, but as soon as they move into a noisy environment with a lot of reverberation or ambient noise, their ability to hold a conversation is drastically reduced.
These noisy environments are so challenging for unilaterally deaf individuals because of the way our brains collect and process information. Our ears collectively gather acoustic information and relay it to the auditory cortex of our brains. Your brain is designed to get information from both ears, so when only one ear is collecting that information, your brain is starved for information. The brain automatically thinks this is an error, so your brain compensates through a variety of different mechanisms:
- Head Shadow Effect: When a sound is directed toward the deaf ear, the sound doesn't process in that ear. When it gets there, the sound is slightly muffled because the sound is blocked by your head. Some sounds, primarily high-pitched ones, might be entirely blocked. This becomes a major issue when trying to process voiceless consonant sounds, like the s, c, f, t, p, ch and sh sounds, which are higher-pitched. This makes it particularly difficult to differentiate words.
- Localization Ability: In addition to processing conversation, your brain uses auditory information to locate where a sound is coming from. A combination of the sound's time of arrival at each ear and its intensity tells your brain approximately where a sound is coming from.
When you only have one hearing ear, however, everything seems like it’s coming from one side only — the side of your good ear. This means a person with unilateral hearing loss may not be able to locate the source of a sound as quickly as a person with no hearing difficulties. Instead of immediately identifying the source of the noise, they have to look around to locate it.
- Sound Summation: Your brain summates the hearing power of both your ears so their power as a whole is greater than the sum of their parts. With two ears, you hear three-times as well as you would with only one. For example, if you hear a barely-audible sound coming from a location 20 feet away with one ear, you would be able to hear the same sound 60 feet away with both ears.
This effect, called the binaural summation effect, is the result of your auditory nerves crossing before they connect to your auditory cortex. As they cross, the signals they send amplify, enhancing any sound the ears may hear. Without the hearing ability of one ear, you don't just lose half your hearing — you lose two- thirds of your hearing power.
- Noise Squelch: The neural sharing that results in sound summation also contributes to noise squelch, also known as “binaural squelch” when listening in an environment with background noise. This binaural squelch provides listeners with a three-decibel differentiation between a particular sound and the background noise. This is a significant difference that can help the listener more easily understand conversations in noisy environments. Without bilateral hearing, there is no neural sharing and noise squelch is no longer possible.
In combination, these aspects of hearing make unilateral hearing loss a severely detrimental condition.
Hearing Aids for Unilateral Hearing Loss
Hearing aids for unilateral hearing loss are somewhat similar to those people use for bilateral or complete hearing loss. The type of hearing aid the patient uses depends more on the degree of hearing loss in the ear. Depending on this severity, the hearing aid a patient might use includes:
- CROS Hearing Aids: This is the most traditional hearing solution for unilateral hearing loss patients. Standing for "Contralateral Routing of Sound," these types of hearing aids pick up sounds from the deaf ear and transmit them to a receiver located in the undamaged ear. This minimizes the head shadow effect, but doesn't help individuals' localization ability and, since the bad ear is still deaf, doesn't return the neural activity necessary for noise squelch or summation to occur.
- BTE Hearing Aids: For cases of unilateral hearing loss where the damaged ear is not deaf, a behind-the-ear, or BTE, system is another standard option. This aid amplifies the sound that reaches that ear, relaying it at a stronger frequency into the wearer's ear. This helps with all aspects of hearing, but does take some time to get used to.
- BAHA Hearing Aids: A surgical solution for unilateral deafness is the bone-anchored hearing aid, or BAHA. This newer option uses bone conduction to send sounds from the bad ear to the healthy ear using an implant that magnetically attaches to an implant under the scalp. Just like with CROS hearing aids, this type of solution doesn't help with noise squelch or summation, and only a few cases have found improvements in localization following implantation. This mostly helps minimize the head shadow effect.
If you’re dealing with unilateral hearing loss or simply want to learn more about hearing impairment conditions, speak with your doctor or book a free hearing evaluation with us.