One Ear Hearing
is a Disability
One Ear Hearing is a Disability
What is the effect of single-sided hearing loss on my child’s function and development?
Dr. Joseph Roberson
The Center for Atresia & Microtia Repair
California Ear Institute
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 is wrong. Single-ear hearing loss is a disability.
Single-sided hearing loss produces several functional and developmental problems. As an overview statement based on well-done research, it is fair to say, “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. That same child may have extreme difficulty in a noisy classroom.
Another critical principle to understand is this: development of functional hearing ability occurs mainly in the first 5-6 years of life. If single-sided hearing loss is present during the first 5-6 years of life, of the patient’s hearing function will be negatively affected, and the deficit shows up around 4th or 5th grade. More importantly, if hearing deficits are present and untreated during the period of development in the first years of life, the functional deficit is very likely to be lifelong. It is for these reasons we are so passionate about ensuring hearing from both ears is established in early childhood – to prevent lifelong hearing disability that affects your child’s life.
Let’s be more scientific. First, you need to understand the basics of auditory function. In the simplest description, the ear canal, 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.
It is the ears’ job to present all noise in the environment to the brain. The brain’s job is to process those sounds. For example, our hearing world is full of noise that is useless to our function. The brain’s function is to filter out those sounds we don’t need (like when we are listening to the teacher and the airflow from hearing ducts and the noise from outside the classroom are going on at the same time).
We have all had the experience of being in a very noisy restaurant and trying to listen to someone across the table from us. Even with normal two-ear hearing, it can be hard to understand a conversation when background noise levels go up. With single-sided hearing loss, even a small amount of noise in the background creates significant problems understanding spoken language. The restaurant example is a practical case study of the challenges someone with single-sided hearing experiences in comparison to people with normal hearing.
Here are summaries of the different functions two-ear hearing allows:
Sound Localization (Directional Sound):
When a sound comes at us from any angle, the brain measures the difference in the 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. While this timing difference is very small, it allows the brain to “localize” the source, and the listener can turn to it if desired. With single-sided hearing loss, this ability is lost. 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. This is one reason children with hearing loss have a higher rate of injury and admission to the hospital emergency room than those with normal hearing in both ears since they cannot localize threats such as a car in a parking lot or a bicycle approaching from behind.
Hearing in Noise
Every day, we select 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, and separate information streams must come into each ear separately for the brain to have the ability to produce selective listening. Without two ears, the brain lacks the input needed to perform this function, and as a result, 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 (like Autism), 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.
Importantly, implantable hearing aids (also called bone conduction hearing aids like Osia, BAHA, Ponto, etc.) do not give improved hearing in noise. Bone conduction hearing aids send the same sound information to each inner ear simultaneously and simply amplify the volume of all sound, resulting in mismatched signals between the normal hearing ear and the device signal. As a result, in noisy places, a high percentage of users remove the bone conduction hearing aid because their function deteriorates instead of being improved. Patients will describe it this way: “When I am trying to listen in a noisy place with my bone conduction hearing aid on, it confuses me when sound comes into my normal ear the usual way, and then on top of that, a signal from the hearing aid confuses my brain… I end up taking it off when background noise increases.”
Binaural Loudness Summation
When two ears hear a sound, it registers as louder with the brain. Nerve cells in the brain which register sound receive input by neural connections called axons from 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.
Head Shadow Effect
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 (ALL classrooms are noisy to some extent) and imagine what happens when the teacher walks to the patient’s side with hearing loss. With that image, you can understand how two ears are preferable to a single ear in the classroom and in other life situations.
What data shows these effects?
Multiple scientific studies have shown the effects of single-sided hearing on children in several different areas of study (including hearing aids, cochlear implants, atresia-microtia, and others). I will list a few that are referenced in the papers at the end of this communication
Sounds Localization
Almost all parents understand this phenomenon from watching their children. Sound localization requires low-frequency hearing above 50 dB at 500 Hz for the brain to be able to perform this function. Within 2-3 months of achieving hearing from two ears (like after an ear canal surgery for congenital aural atresia), a child will begin to be able to tell where a sound originates. Progressive adaptations continue to occur for several more months.
Hearing in Noise
Patients with two normal hearing ears are placed in a testing booth, and speech understanding is tested with varying degrees of background noise. In the noisy restaurant example cited previously, normal-hearing individuals will see their speech comprehension fall from 100% in quiet to 90-95% in background noise. For single-sided hearing subjects, speech comprehension is also 100% in quiet but falls to 60-65% understanding in background noise. This is the reason we see children with single-sided hearing loss repeat a grade 30% of the time. It is also the reason we see children with single-sided hearing loss exhibit behavior problems in school, including a lack of concentration, anger or frustration, detachment, poor learning, and aversion to school. These behaviors are simply because it is so frustrating to hear and learn in a noisy place for them. It is also the reason that adults with single-sided hearing loss earn 1/3 less in salary on average than their normal hearing peers. As shared earlier, single-sided hearing loss is a disability.
So, what impact should this have on how I treat my child?
The brain’s ability to hear in noise and to speak is not present at birth and must develop. This majority of this capability develops in the first six years of life when both ears send sound to the brain. Continuing development at a slower rate continues into the teenage years. If this period of development is missed, the brain no longer has the same ability to learn and change.
One practical example of this phenomenon is a person’s accent. For example, I have an accent that someone from the United States can identify as being from the Southern States. An accent is nearly impossible to change after it is learned and set in place. Many of our body systems are similarly constructed with this phenomenon doctors call “critical periods of development”. Waiting until late in the critical period of development - or even after it - to provide hearing in two 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 possible, as early as possible.
Many physicians have been taught that one ear is good enough, and due to this error, many do not recommend treatment of single-sided deafness, or may recommend it later in life if problems are observed. For some physicians who are not up to date about these facts, there is no perceived problem 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 is entirely false and can be permanently damaging to the patient’s hearing function. It is almost routine for us to have parents tell us their pediatrician, plastic surgeon, or other health professional advised them that it is not necessary to have two hearing ears. Now, you know that advice is wrong – and you know not to follow it.
Each patient’s individual situation must be assessed by a hearing professional able to evaluate treatment options and to estimate chances of success. Each patient must have information and data gathered to be accurate in these opinions. I am continuously impressed as to how the plan for different children widely differs. These options may change over time as well. For example, surgery to create an ear canal (atresia repair canalplasty) may be the right choice if a CT shows a high chance of success at the appropriate age. On the other hand, wearing a softband bone conduction hearing aid may be the right thing to do to stimulate the ear with single-sided atresia from a few weeks of age until evaluation for surgery is possible, or may ultimately be implanted in patients who are not candidates for canal surgery.
As a parent making decisions about whether or when to treat a child with single-sided Atresia Microtia, the information above allows you to have a critically important understanding. For hearing function, intervention to allow normal development must occur at an early age. We recommend intervention between 3 and 5 years of age as the best time for surgery and frequently use hearing devices before that to achieve some brain development. Intervention must occur before the deficit in hearing becomes evident in a child’s life. I have multiple teenage patients whose parents chose not to supply hearing at an early age who return in the range of 5-7th grade after telling their parents, “I can’t hear and need help.”
Children who have hearing restoration in two ears in early life can and do develop and function normally as they age into adulthood.
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