Tag Archives: hearing

WHAT IS THE VESTIBULAR SYSTEM ?

VESTIBULAR SYSTEM DEFINED

Rocking, swaying, spinning, bouncing, carrying, and jiggling are techniques instinctively used by parents with baby to calm, soothe, and induce sleep.  Why?  Because of their effect on the vestibular system.  Considered to be one of baby’s most highly developed senses at birth, the vestibular system is responsible for balance and motion perception.  It also plays an essential role in maintaining the head and body posture.

ANATOMY OF THE VESTIBULAR SYSTEM

Located in the skull, in a small space called the vestibule, the vestibular apparatus consists of three semi-circular canals.  Each canal is filled with fluid and lined with tiny hairs.  When the fluid moves it stimulates the hairs and triggers a series of electrical signals which send information to the brain.  The superior, horizontal, and posterior canals, as they are named, are situated in different directions or angles from one another.  Thus, one canal may be stimulated more than another depending on our direction and plane of movement.  This stimulation sends the signals to the brain which tell us our position in space and provide balance.  The vestibule also houses the inner ear and the otolith organs.  Some motion such as head tilts and linear movements are sensed by the otolith organs.

PRENATAL VESTIBULAR STIMULATION

In 1922, Minkowski identified the vestibular system as well-developed in early human fetuses.  Minkowski became noted for his research and findings on fetal development.  During the prenatal period, the fetus experiences a lot of moving around due to the constantly changing position within the warm amniotic fluid that cushions her from the outside world.  The fetus experiences positional changes relative to gravity as well.  When the mother is standing up the weight of the fetus shifts in response to gravity and when the mother is sleeping on her back the fetus moves in a different direction in response to this orientation.  These are examples of the kind of passive motion stimulation the fetus receives during the prenatal period.  All three canals in the vestibular system sense these changes in position and motion.

Later in the pregnancy the mother begins to feel the baby kicking and other reflexive movements, adding to the motion stimulation.  Because the level of prenatal motion is particularly high, after birth the baby will probably not experience the same degree of vestibular stimulation until she starts independently walking.

POSTNATAL VESTIBULAR STIMULATION

Parents quickly learn that baby responds quite well to motion.  From rocking baby to sleep to spinning in a circle with baby to thwart her fussiness, parents turn again and again to motion for inducing calm, quiet, and sleepy states of their infant.  The vestibular system is stimulated with these activities and that is a familiar and welcome feeling to baby.  The acquisition of motor skills that move the head and body in space offer a lot of vestibular stimulation that is self-induced. This is part of the pleasure in the movement for baby.  Not only do they get the “feeling” of the movement, but they can create it for themselves whenever they want.  For example, rolling across the floor moves the vestibular apparatus around and around with each roll.  Another example is the skill of lifting the head up and down while in tummy time.  Research suggests that these activities improve the brain and mind development.


BABY HEARING: LOUD NOISES

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DEVELOPMENT OF BABY HEARING

The fetus in the womb hears sound that is transmitted by liquid, which softens or muffles the sounds to some extent.  After birth, babies hear a variety of sounds, yet tend to be disturbed only by the sudden loud noises.  These “violent” sounds elicit the startle reflex, seen as a jerking of the head backward, bulging of the eyes, and flexion of the elbows.

ANATOMY OF BABY’S EAR

There are two distinct branches of the auditory nerve.  One is the cochlear branch which carries sound information to the brain and the other is the vestibular branch which detects motion and tells us where we are in space.  Anatomy books show how closely these two branches are interconnected.  We also know that the stimulation of a nerve in a baby travels through the body more than in an adult.  For example, if you scratch a baby’s foot, the muscles of the entire body respond.  When a baby hears a loud sound, since these two branches are close together and newly developing, the strong stimulus travels over to the vestibular branch of the same nerve.  Thus, the baby not only hears the sound (cochlear branch) but physically feels it in his limbs (vestibular branch).  His head jerks backward, deepening the physical sensation when the movement of the fluid in the ear further stimulates the vestibular branch.  It is possibly experienced as pain, suggests Dr. Moshe Feldenkrais in his book The Elusive Obvious, which examines fundamental physiology patterns in humans.

The above video from oleviasea’s youtube channel is one clear example of this reaction.  In this situation, the father’s snoring is staged, but the baby’s reaction is not.  The noise is indeed near the threshold of feeling.


FETAL HEARING

HEARING IN THE WOMB

Why does a baby feel comforted by her mother’s voice or  soothed by the sound of her mother’s heartbeat?  The sense of hearing develops quite early in the womb. As sound penetrates the wall of the mother’s abdomen which surrounds baby, this sense has the chance to develop quite a bit before birth.  By the early age of six months of fetal development, baby is able to respond to sounds.  And with each passing week, baby hears an increased range of both volume and frequencies.  At birth, baby has 12 weeks experience hearing a variety of sounds from both the internal world of the mother’s body and the external environment into which it emerges.

When my friend Erin was pregnant with her son Jasper, I remember her telling me how much he moved when her tea kettle boiled water.  This particular kettle had a lower-pitched choo-choo train whistle that her unborn son could hear.   Later in her pregnancy the family vacationed in Yosemite and Jasper had the same reaction to the sound of the waterfalls. “Whoosh!,” she described the action in her belly as he responded to the thundering sound of crashing water.  These sounds fit right into the categories of what qualities and types of sound a fetus hears.  Research conducted on women in the first stage of labor has taught us what sounds cross the abdominal wall and introduce baby to their sonic future.

TYPES OF SOUND A FETUS HEARS

  1. Mother’s Voice (baby hears mothers voices louder than others because it does not need to penetrate the wall of the womb)
  2. Bodily Sounds of the Mother (i.e., heartbeat, blood flowing, stomach gurgling)
  3. External Sounds from the Environment (i.e., music, voices, trains, planes, waterfalls)

QUALITIES OF THE SOUND A FETUS HEARS

  1. Mid-Low Pitch
  2. Loud Volume (louder than normal conversation, but too loud is damaging to hearing)

In 1980, the journal Science presented a study on newborns.  Pregnant women read their unborn child a passage from Dr. Seuss’ To Think That I Saw It on Mulberry Street.   They read the passage several times.  After birth, the newborns were outfitted with nipples which controlled what they heard.  They could change the sound of the voice simply through their sucking, one of their earliest voluntary actions. They were listening to a recording of various women reading the Dr. Seuss passage, and one of the women was the mother of the baby.  This study found that newborns preferred to listen to the voice of the voice of the mother.

BABIES, SOUND AND MOVEMENT

How does this research on sound influence learning movement?  Since hearing is more developed than sight, use the sound of your voice to reassure the baby when learning new skills, choose toys and rattles with sounds to guide them in the process of seeing and playing with objects, recall what “familiar” in-utero sounds may be comforting, and, most importantly, SING as a method of play.


BOOK REVIEW: “WHAT’S GOING ON IN THERE ?”

Child development book "What's Going On In There" by Lise Eliot

While holding your blinking infant in your arms, watching your toddler run toward music, or observing your five-year-old remember some tiny detail from last Christmas, did you ever wonder how the infinitely complex brain, five senses, and memory of these little ones develop?  So did Lise Eliot, Ph.D., a neurobiologist and assistant professor at Chicago Medical School.  Eliot, mother of three, could not find a book that sufficiently answered her questions, so she researched and wrote one herself.  The result is a “must add to your bookshelf” reference for pre-pregnancy through age five or anyone interested in infant development.

What’s Going On in There:  How the Brain and Mind Develop in the first Five Years of Life, published in 1999, is thoroughly researched, well organized and indexed, and easy to read.  Eliot explores the development of the five senses, language, emotions, memory, and cognition.  Rather than just a treatise of scientific explanations on the development of these processes, Eliot focuses on what parents can do to raise a smarter child.  What I love most about this book (beside, of course, the content) is the organization.  When you have a thought such as “If we took our 5 month old with us to Hawaii, would he remember it?” or “What can I do to stimulate language development,” just look in the index and read the corresponding pages.  Read as much or as little as you would like, but either way, in a very short time you will have your answer.

What’s Going On in There:  How the Brain and Mind develop in the First Five Years of Life:  by Lise Eliot, Ph.D., (New York: Bantam Books, 1999).


PROPRIOCEPTION: HAND AND ARM COORDINATION

PROPRIOCEPTION TIPS:  Rattles and Sound Variations

IVAN’S STORY- THE NORTH STAR

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Ivan, the first of our stellar caterpillars, is our “North Star.”  Ivan received his first lesson at four weeks of age and continued lessons until he walked on his own at twelve months. At six weeks Ivan learned to hold and shake a rattle.  This tiny yellow maraca swishing around made its quick sounds from grains of sand inside.  Swish-swish-swish, a smile grew bigger on Ivan’s face, swish-swish-swish.  At each successive lesson, when Ivan began to cry, his attention could quickly be recaptured by shaking a rattle with an interesting sound.  We played with several different rattles:  one made the swish of grains of sand, another the ding of a bell, yet another the jingle of several bells, and one the percussive chop of wood.

Babies and Sound

Babies respond to novelty, especially with sound.  Think “new, different, unusual” when choosing rattles.  The variations stimulate their curiosity and catch their attention.  And, when they shake the rattle, they enjoy the feeling that they can create this unusual sound that they hear!  The sound also helps the baby to learn where his hand is in space.  The ability to know and feel “Now my hand is close to my face,” or “Now my hand is close to my chest,” is facilitated by the sound of the object and the feeling of the object touching his face or chest.  This skill is called proprioception.  Proprioception is defined as the ability to sense oneself in space, or to feel a part of the body in space.  This can be the location, position, movement, and orientation of the body as a whole, or of the body part.  In this example we are talking about the baby learning proprioception of his arm and hand.  The baby both hears and feels his hand is close to his face when he simultaneously hears the bell jingle and the feels the bop on his nose.  A rattle that makes a sound offers a very important clue to the baby as he is learning this coordination.

Ivan’s curiosity with sound continues today as he taps around on his first drum set, or on the drums of another musician.  Recently, while attending a wedding with his parents, Ivan caught sight of the drummer and walked up very close to him and stood, carefully watching him play.  Soon, the drummer stepped aside and let Ivan “sit in” on the next song.  Ivan moved his drumstick from one drum to the next to the cymbal….exploring how many different sounds he could make!  Our North Star leads the way!