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Effects of Hearing Loss on Auditory Development

Hearing is present before birth.  As mothers know, babies in the womb will respond to sound starting at 26-28 weeks.  After birth, hearing and language development are strongly linked together during the first few years of growth and development.  Normal language and brain development requires normal hearing.  For example, children who are deaf and have no hearing input do not learn to speak normally.  It is important to understand that partial hearing loss also affects the normal developmental process.

Hearing loss with AM is due to a lack of sound transmission into the inner ear.  With AM, the middle ear bones are present but are usually mildly malformed, the inner ear including the hearing nerve is normal but the ear canal and eardrum are malformed, blocking sound from reaching middle and inner ear.  In most, but not all cases, the pinna is malformed as well.  Nine out of ten cases of AM are single sided but in 10% of cases,  both ears are involved.

Malformation of the ear

Note bilateral AM requires special attention to achieve hearing with special devices soon after birth or severe abnormalities may result.  Single sided hearing loss due to AM also requires attention to achieve normal function.

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It is very important to understand this:  the effects of hearing loss on development will become permanent if not treated in childhood.  The hearing system’s receiver (the ear structures detailed above) is present and working at birth.  The brain’s connections, however are incomplete at birth and must be constructed (we call that learning) after birth. This learning occurs by hearing sounds, learning to speak, and associating written and spoken words in reading and other hearing activities.  Think of this system as a seed that needs to be planted in a good soil to grow.  Sound is the water and sunlight that causes that seed to sprout and grow into the most vibrant plant it can become.  Time spent without full sunlight and water (like partial hearing loss or single sided hearing loss or the more severe bilateral AM) will reduce the outcome of the brain system from developing to its full potential.

A practical example of how the auditory system becomes ‘set in stone’ is by examining accents people have.  These are learned in childhood in the first few years of life and are virtually impossible to change.  Another example is the Japanese language which does not include the sound for /r/.  In adulthood, it can be impossible for someone who grows up in Japan speaking only Japanese to pronounce words with the /r/ sound.Hearing is a system that has a critical period of development.  Developmental specialists know that this means if sound input is not received early in life, the system will not develop at a later date.  In the human auditory system, the first five years of life are particularly important with the great majority of auditory brain development occurring during that time period.  For auditory and brain development, early sound stimulation is best for maximum results.  It is for this reason we recommend hearing reconstruction earlier than any other group.

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