Hearing Loss in Children: a risk factor for speech and language impairment.
Hearing loss in children is a frequent contributing factor in speech and language impairment. A hearing loss can cause a speech or language disorder in some cases, or it can worsen an already existing speech or language disorder. For this reason,
a hearing test is usually a part of a full speech-language evaluation.
If you think about it, it makes sense. To be capable of good language output, you have to have adequate input, and for most languages (sign languages being the obvious exception), the input has to travel through the ears to get to the brain. Hearing loss in children results in limited access to the speech sounds, vocabulary, and grammatical structures of their language; if their hearing loss goes undiagnosed and untreated during the first few years of life, it can have a lasting negative effect on their speech and language development.
What do I know, anyway?
In this section, as in the rest of my site, I am speaking out of my training and experience as a speech-language pathologist. As such, I have some basic training in audiology, but not to the extent that an audiologist would have. In my capacity as a speech-language pathologist, I do not perform full audiological evaluations or make recommendations regarding hearing aids or other amplification devices. I do perform hearing screenings, which are a simple pass-fail measure; if a child fails a screening, I refer the parents to an audiologist for further testing. If a child is diagnosed with a hearing loss, a speech-language pathologist often provides audiological rehabilitation to strengthen listening and auditory processing skills.
I am also speaking here as the father of a child with a unilateral hearing loss. My daughter was diagnosed with a moderately severe mixed hearing loss in the left ear at about age three. I'll talk more about her on my page about unilateral hearing loss.
All hearing losses are not created equal
The first thing to remember about hearing loss in children is that it can come in many different forms. Here are some pages that will help you understand the variety of hearing losses that are possible, and how they affect speech and language development in children:
Different degrees of hearing loss in children
Different types of hearing loss in children
Before you click through, you may want to familiarize yourself with a few terms (or remember where they are and come back as needed):
- The decibel scale is what we use to measure the loudness (a.k.a. intensity, amplitude) of sounds. The higher the number of decibels (dB), the louder the sound. The decibel scale is a bit tricky in that it is logarithmic instead of linear. Every increase of 10 dB is ten times louder (20dB is 10 times louder than 10 dB; 30 dB is 10 times louder than 20 dB, and 100 times louder than 10 dB, and so on). Also, keep in mind that zero decibels (0dB) is not a complete absence of sound; it is the quietest level at which the average healthy, young ear can hear sound. Some people can hear sounds at -5dB or even -10dB. Although most of us cannot hear sounds quieter than that, complete absence of sound can only exist in a vacuum, where there is no material for sound waves to travel through.
- Hearing threshold is the quietest level at which a person can hear a sound. Thresholds between 0dB and 20dB are usually considered to be in the normal range. Lower thresholds indicate better hearing; people with thresholds above 20 dB are considered to have a hearing loss. A person may have a different threshold in the left ear than in the right. It's also common for thresholds to vary according to the frequency (pitch) of a sound. Hunters (especially those who don't wear hearing protection) sometimes have elevated thresholds for high frequencies corresponding to the those produced by gun blasts, but normal thresholds for lower-frequency sounds.
- Frequency is the way we measure the pitch of a sound--how high or low it is. We measure frequency in cycles per second (CPS), also called Hertz (Hz). Sound is caused by vibrations, and the faster something vibrates (i.e., more cycles per second), the higher the sound will be. A typical adult speaking voice ranges from 100 Hz to 220 Hz on average; male voices tend to be at the lower end of that range, and female voices are usually toward the upper end. However, as we speak, we also produce higher frequencies, called harmonics or overtones, and it is these frequencies that change as we produce speech sounds. We need to be able to hear frequencies up to around 3000 Hz to be able to hear vowel sounds clearly, and to hear the difference between /s/ and /sh/ we need to hear up to between 7000 and 8000 Hz. Some types of hearing loss affect our ability to hear all frequencies equally, while others will affect some frequencies more than others. For example, noise-induced hearing loss often affects the higher frequencies more than the lower ones.
Causes and prevention of hearing loss in children
Causes of hearing loss in children include a variety of genetic and environmental factors. About 50% of hearing losses are due to genetic factors. Some of these are recessive, so it is possible for a child of two parents with normal hearing to be born with a genetic hearing loss. Some environmental factors can cause hearing loss in children before birth (for example, the mother contracts rubella or cytomegalovirus during pregnancy), while others, like otitis media (middle ear infections), ototoxic medications, or noise exposure may cause hearing loss in children after birth.
Because so many cases of hearing loss are caused by environmental factors, education about hearing loss prevention can have a powerful effect on reducing the prevalence of hearing loss in children. Advances in medical diagnosis and treatment have reduced the incidence of illnesses that can cause hearing loss; at the same time, public education efforts have raised awareness of the dangers of noise exposure and the importance of hearing protection in noisy environments.
A fluctuating hearing loss may be caused by recurring bouts of otitis media. Fluid builds up in the middle ear and causes a conductive hearing loss. When the infection goes away, the fluid is re-absorbed (or drains out through a ruptured eardrum) and hearing returns to normal; however, the risk is always there that a viral infection could spread to the inner ear and result in a permanent hearing loss.
A temporary hearing loss may also result from an ear infection. Another possible cause is a build-up of ear wax, or cerumen, in the ear canal. Some people produce more cerumen than average and their ears become blocked as a result, unless they are proactive about managing the build-up. Ear wax buildup rarely causes hearing loss in children, however. Far more common is self-inflicted (or parent-inflicted) blockage of ear wax through the use of cotton swabs (Q-tips) to "clean" the ears. What many people do not realize is that swabs only remove a small amount of ear wax, and actually push most of it farther into the canal, where it hardens and eventually blocks the canal. Always consult a doctor before attempting to remove ear wax from your own ear or from your child's.
Diagnosing hearing loss in children
Until not too long ago, hearing loss in children tended to go undetected until a parent or other family member (usually the mother) noticed that something did not seem right. In the case of a severe hearing loss or deafness, the child might have been between one and two years in age when the parents noticed an absence of response to sound, such as turning toward a parent's voice, waking or startling at loud noises, and so on. Because children with less severe hearing loss, or a loss in just one ear, do respond to sound, these cases were often discovered even later, sometimes not until the child was in school. This is unfortunate, because the first years of a child's life are so important for speech and language development. Hearing losses that go undetected during this time can cause serious setbacks to speech, language, literacy, social interaction, and academic success.
Today, many industrialized nations require universal newborn screening for all babies born in hospitals. Newborns who fail the initial screening are re-screened, and if they fail the second screen, they are referred to an audiologist for a more thorough examination.
If the only kind of hearing test you have ever experienced is the one where you wear a headset and raise your hand when you hear a 'beep', you may be wondering how on earth one would test a newborn's hearing. The answer is that there are several passive tests to check how different parts of the auditory system are working. One type of test measures otoacoustic emissions (OAE), which are 'echoes' produced by the inner ear in response to sound. An earplug with both a speaker and a microphone are placed in the ear canal; the speaker emits a sound, and the microphone detects the echo. Another test detects auditory brainstem responses (ABR), or brainwaves produced in response to sound. Electrodes placed on the scalp detect activity in the brainstem following presentation of a tone through an earplug. For both of these tests, it is unnecessary for the child to raise a hand or indicate in any other way whether he heard the sound. In fact, the quieter and less active the child is, the better, and for ABR testing, it's best for the child to be asleep during the procedure.
It is important for parents, teachers, and others who work with children to be aware of the symptoms of hearing loss in children. There are two main reasons for this. First, I've never heard of a child going to his parent or teacher and saying, "You know, I think I may have a hearing loss. Maybe I should get tested." Children with a hearing loss are often unaware that anything is wrong with their hearing. They may notice that the grown-ups and other kids around them mumble a lot and then get upset with them when they don't understand, but it does not occur to them that this is due to their ears not working properly. Reason number two is that, when children miss something you say, they do not generally cup a hand behind their ear and say, "Eh? Speak up, sonny, I can't hear you!" In fact, if you ask them directly whether they heard you, children (with or without hearing disorders) will often answer "yes", because this is what they think you want to hear. The signs and symptoms of hearing loss in children are much more subtle, and adults who do not have hearing loss on their mind may easily mistake them for something else, like attention deficit disorder, a learning disability, autism, or just plain willfulness.
Symptoms of hearing loss in children will vary in their obviousness depending on the type and severity of the hearing loss. Common warning signs include:
- not responding to a parent's voice at normal speaking level
- absent startle response to loud sounds (with some types of hearing loss, however, loud sounds are amplified, even painful, and the child does startle.
- inability to localize the source (tell where a sound is coming from)
- difficulty following instructions or requests, despite appearing to listen attentively
- reduced or absent responses to environmental noises (car horns, approaching footsteps, sirens outside, telephone ringing, doors opening or closing etc.)
- consistently setting the volume at an unusually high level when watching television or listening to the radio.
- enjoyment of rhythmic clapping games while appearing uninterested in music
- immature speech-language development
- social withdrawal
- fatigue, frustration, and acting out
Treating hearing loss in children
Some types of conductive hearing loss can be corrected with surgery, or by removal of impacted ear wax. However, most hearing losses are not curable. Treatment usually focuses on some combination of the following elements:
- amplification, including some combination of analog or digital hearing aids, cochlear implants, or FM transmitter systems.
- compensatory strategies, such as lip reading, signing, cued speech, optimal seating/positioning, elimination of background noise.
- prevention of further loss through education on environmental risk factors, such as loud noises, ototoxic medications, and exposure to diseases that can damage the auditory system.
- cochlear implants, which use electrical impulses to stimulate the auditory nerve directly, bypassing the hearing organs
Hearing loss in children is a huge topic and one could build an entire web site devoted to it. The information I've provided is a good start, but it barely scratches the surface of all there is to know about hearing loss. If you suspect your child has a hearing loss, you should definitely ask your doctor for a referral to an audiologist for a full evaluation. Hearing loss does not have to be a barrier to education or to a happy, fulfilling life--if you are proactive about it.
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