ATRESIA MICROTIA & YOUR CHILD
Chapter 1: Hearing and Language Development
Chapter At-A-Glance
In this chapter, we will look at: HEARING BASICS: What sound is and how hearing works LANGUAGE FUNDAMENTALS: How children develop the ability to understand and use speech HEARING LOSS: How hearing loss impacts children’s entire lives |
How Normal Hearing and Sound Work
Although they may be tiny, children’s hearing systems are mighty. With the precision of finely tuned instruments, their ears capture and process sound waves—ultimately delivering them to their brains as electrical signals.
This section describes that process.
First, What Is Sound?
Sound is a complex vibration transmitted through the air. Imagine a stone being thrown into a pond. When the stone hits the water, a wave goes out in all directions. Sound operates similarly.
Sound enters the outer ear and travels down the ear canal. It then travels through the eardrum, making the ossicles vibrate in the middle ear.
How Does Sound Work?
When something makes a sound, vibrations travel away from the source in all directions. If people are in hearing range, their outer ears capture and send sound waves down their ear canals to their eardrums.
The Components of the Hearing System
The Ear and Ear Canal
The outer ear captures sound waves nearby and sends them down the ear canal.
The average hearing system captures more than 99.9% of the sound waves that enter the ear canal!
The Eardrum
The eardrum (or tympanic membrane in the graphic) is covered with skin. It has a middle layer of connective tissue and is covered inside with the same tissue that lines our nose and mouth, called mucosa. For hearing to work correctly, the thin tissue membrane needs air on both sides so that it can vibrate freely. When the sound wave strikes the eardrum, a tiny in-and-out vibration occurs.
Middle Ear Bones
The three middle ear bones (called ossicles in medical terminology) then transmit this vibration into the fluid-filled cochlea.
The Cochlea
The cochlea is filled with fluid and lined with tiny structures called nerve receptor hair cells. These cells look like little hairs and sway when sound vibrations make the fluid in the cochlea move. Think of these hair cells as thin blades of grass on the bottom of a pond. As the current moves, the grass sways to and fro. The movement of the hair cells makes them fire electrical impulses.
The Auditory Nerve
The auditory nerve receives the electrical signals from the hair cells and carries the electrical impulse generated by the nerve receptor cells to the brain.
The Brain
The brain is the hearing system’s central processing center for incoming electrical signals, almost like a computer. Here, the electrical impulses are identified as sound and decoded to interpret their inherent meaning.
The entire hearing system is so tiny that the whole inner ear is filled with only a few drops of fluid. Surgeons must use microscopes to perform ear operations!
How Hearing Components Work Together to Create Sound
People normally think of the outer ear when they hear the word ear. The ear canal works like a tunnel, carrying sound from the outer ear to the eardrum. The eardrum passes sound vibrations to the middle ear bones, or ossicles, which deliver the sound vibrations to the inner ear. Called the cochlea, the inner ear is filled with fluid. It’s responsible for converting the vibrations into electrical signals that the brain then interprets.
Normal anatomy of the human ear. Sound waves are transmitted through the ear canal, striking the ear drum, and are then transmitted to the inner ear (cochlea).
Vibrations entering the fluid-filled inner ear stimulate hair cells within the cochlea, triggering electrical signals which are carried by the hearing nerve to the brain, where they are interpreted as sound.
How the Hearing System Develops
Hearing systems begin to develop early during pregnancy—beginning almost immediately after conception. Development occurs in three phases and is complete within the first trimester.
Three Stages of Prenatal Hearing Development
The ear develops early in pregnancy in three stages. 1. The inner ear is nearly complete one month after conception. 2. The ear canal is formed before most women even know they’re pregnant. 3. At 52 days, the outer ear has formed. |
Stage 1: Inner Ear
The inner ear begins to form when the fetus is tiny and is nearly complete one month after conception. The cochlea starts off as a ball of cells. It then migrates to the skull base and forms that structure.
Inner ear development is completed within the first month of
gestation. The development of these structures is typically normal in patients with CAAM.
Stage 2: Ear Canal
After the inner ear forms, the ear canal develops. It starts growing from the outside of the skull, where the ear canal is visible externally and grows toward the inner ear. A similar opening also grows from the back of the throat at the same time.
When the two tracts meet, the open ear canal is formed, with the eardrum in between. This process is complete before most women even know they’re pregnant.
Stage 3: Outer Ear
The outer ear develops last. Six mounds of tissue form, grow, rotate, and fuse to make the outer ear. At 52 days, the outer ear is completely formed.
Development of the outer ear structures in utero. The outer ear
develops last and is completely formed by two months after
conception.
How Hearing Impacts Learning and Language Development
Your child’s ability to speak, read, and write is inextricably linked to hearing normally. Without sound or hearing, speech does not develop as it can and should, even from before birth. Limited access to hearing and sound can also limit your child’s capacity to read and write.
Studies show many adults with total hearing loss read at an average of elementary school level, likely because of limited access to sound! This is a sensitive topic for some individuals.
Sound only stimulates a child’s hearing growth maximally for a limited period. If they miss this critical window, children lose the opportunity to develop normal hearing forever. The overwhelming majority of hearing and language development occurs within the first five years of life and is mostly complete by early teenage years.
Stages of normal auditory development by age in years: receptive language (0-3 years), expressive language (1-5 years), and complex language (3-10 years).
How Children Learn to Speak
Normally, hearing children develop receptive language before they speak any words.
Receptive language is the ability to understand spoken words. It develops before children are able to say them.
When you learn a new language, it’s often easier to understand than speak it, especially at first. Similarly, children understand words even before they themselves can talk. For example, when my children were about 12 months, they got excited when I asked if they wanted a cookie, even though they lacked the vocabulary to ask for one themselves.
The period of maximal receptive language development ranges from roughly from birth to three years of age.
When Do Children Develop the Ability to Speak?
Children generally enter their expressive language phase at about one or two years of age, and development typically lasts about five years. As long as their hearing systems process sound, a child’s vocabulary quickly increases during this time, and their understanding of language structure develops.
Studies show most children speak an average of five words around their first birthday. By the time most are five years old, their vocabulary has blossomed to about 5,000 words.
With normal hearing, it’s amazing how fast children develop!
When Is Hearing Development Complete?
The most complex components of hearing develop between 5 and 10 years of age and continue more slowly into the teenage years. Examples include directional hearing (the ability to locate where a sound is coming from) and hearing in noisy environments.
Sometimes, parents wait to treat hearing loss until too late—often because the effects of hearing loss don’t show up until third or fourth grade, often due to poor school performance. At this point, treatment is usually too late because the critical period for brain and language development has already passed.
The Critical Speech Developmental Window
Even though hearing and language capabilities develop into teenage years, the most critical development period occurs in the first five years of life. While most of the relevant data has been collected from children treated with cochlear implants, the information still applies to hearing development in all children. In medical terms, this period is known as a critical period of development. Many body systems have critical periods of development similar to the hearing system. (I discuss this research in Hear For Life: Dr. Joe’s Guide To Your Child’s Hearing Loss.) As that book states (emphasis added):
Hearing loss is treatable, and treatment may start at birth.
It is extremely important to act quickly once the diagnosis of a child’s hearing impairment is made or suspected.
If critical periods of development are missed, no amount of intervention can correct those losses. The age at which the treatment began is the single most important factor in predicting successful treatment of congenital hearing impairment in children.
In other words, if you don’t treat your child’s hearing loss within the first years of life, the damage can be irreversible. Do something as soon as you find out about it.