Singled Sided Hearing Loss in Children
What is the effect of single sided hearing loss on my child’s function and development?
Traditionally, physicians and audiologists have been taught that if one ear is normal then auditory, speech, and language function and development will be normal. We now know this long-held belief is WRONG.
Untreated single sided hearing loss in children produces several functional and developmental problems. Summarizing the research at the end of this article, it is fair to say that “the more difficult the listening situation the more dysfunctional single sided hearing becomes”. For example, a child with unilateral hearing impairment will function relatively normally at home in a quiet environment with a single person interaction with known speakers. That same child may have extreme difficulty in a noisy classroom. Even if teachers, parents, and professionals think the child is doing “just fine” with hearing only on one side, it is well documented that untreated single sided hearing loss has a significant potential impact to adult earning potential.
Let’s be more scientific. First, you need to understand the basics of auditory function. In the simplest description, the ear canal and eardrum and inner ear serve as a mechanism to convert the vibrational energy of sound in our environment to electrical pulses presented to the brain by the hearing nerve. The brain takes that signal and analyzes it to give us the sensation we know as hearing. In noisy and low volume environments, the brain has to have a signal from both ears to do its job correctly.
We have all had the experience of being in a very noisy restaurant and trying to listen to someone across the table from us. That is a very practical example of what someone with hearing only on one side experiences a significant portion of their day. When children or adults have hearing in one ear only, that same feeling occurs with very low levels of background noise.
Here are summaries of the different functions two ears allow:
When a sound comes at us from any angle the brain measures the difference in time it takes for the sound to reach each ear. For example a sound coming from the right will register in the right ear before it does in the left. This intra-aural time difference is very small, but when two ears hear a sound at slightly different times, the source of the sound can be “localized” and the listener can turn to it if desired. Just like the loss of vision in one eye eliminates depth perception, the loss of hearing in one ear eliminates the hearing equivalent which is sound localization. Imagine yourself on the playground and someone is calling your name and you can hear them but cannot tell where the sound is coming from – that is what hearing with a single ear produces. We believe this is one reason children with hearing loss have almost twice the rate of injury than those with normal hearing in both ears.
Every day we select out the speech we want to listen to from a sea of noise. To go back to our analogy above, all of us have had trouble in very noisy situations (like a restaurant or party) hearing what another was speaking to us. The brain, not the ear, is responsible for our ability to selectively listen in noise. For this system to function correctly, two ear hearing is essential. Without two ears, a child will have difficulty hearing in even small amounts of background noise. Every brain is different in its ability to perform this task and testing can be done to quantify the function. On some occasions, the brain has trouble with this task even when two normally hearing ears are present – called Auditory Neuropathy. Children with one hearing ear have functional Auditory Neuropathy.
Understanding speech in noisy environments while conducting tasks is difficult even for people with normal levels of hearing. The louder the background noise, the longer it takes the individual to complete the task and the more speech they miss. This concept is called “cognitive load” and can represent a subtle but constant problem for school-aged children attempting to understand what a teacher is saying while taking notes in a noisy classroom.
When two ears hear a sound, it registers more loudly with the brain than if the same decibel level sound was only heard with one ear. This makes sense when you know that nerve cells in the brain which register sound receive input via nerve connections called “axons” present in both ears. With a sound, the brain hearing nerve cell will have a stronger stimulation with the same sounds when two ears hear it instead of one. Intelligibility in low volume situations improves significantly with two ears compared to one.
A person with normal hearing and brain function can preferentially listen with one ear instead of the other. Imagine you are walking down a sidewalk with traffic to one side and a friend talking to you from the other. Your brain will preferentially listen to your friend and “turn down” the ear toward traffic to improve your understanding. Now imagine a teacher walking around a classroom (they ALL are noisy to some extent) and imagine what happens when the teacher walks to the side with hearing loss or turns to write on the blackboard. With that image, you can understand how two ears are preferable to a single ear in the classroom and other life situations.
So what impact should this have on how I treat my child?
The brains ability to hear in noise is not present at birth, and develops over time during the first 10-12 years of life. This system only develops fully when both ears are providing auditory input to the brain. Waiting until late in this process to provide hearing in both ears does not make sense from a developmental aspect.
For this reason and the reasons listed above, it is our medical objective to return hearing to two ears if at all possible as early as possible. As stated above, in the past, physicians have been historically taught that one ear is “good enough” and many do not recommend treatment of single sided deafness. These physicians, who are poorly informed about the current research, do not perceive a problem in delaying treatment of single sided hearing loss during the very critical period of development of the auditory system during the first few years of life. Unfortunately, this delay can create permanent and irreparable harm to the child whose hearing loss goes untreated.
Individual situations must be assessed by a professional able to give treatment options and chances of success. These options may change over time as well. For example, surgery to perform atresia repair may be the right choice if a CT shows a high chance of success at the appropriate age. Additionally, soft-band BAHA may be the right treatment to stimulate the ear and hearing nerve with unilateral atresia from a few weeks of age until this CT evaluation for surgery is possible.
Children with Single Sided Hearing Loss should receive a comprehensive medical examination and specialty care from an Otologist, who is an otolaryngologist (ENT) who has undergone two additional years of training and specializes in hearing only. With appropriate medical treatment and therapy, these children can fully function in a hearing world.
Click here to make an appointment with the California Ear Institute to consult with one of our board certified Otologists regarding your child’s ear-related condition.