Infant Toddler Development Training
Module 6, Lesson 3
Anatomy of the Ear
The ear has three parts: 1) the outer or external ear or pinna and the auditory meatus or ear opening; 2) the middle ear, consisting of the eardrum, the middle ear space, and the three small bones that transmit sound energy from the air to the bones and then to the fluid in the inner ear; and 3) the inner ear that is the actual sensory organ that converts energy of sound to electrical signals that go to the brain via the auditory nerve.
Hearing loss is a barrier to perceiving communication that occurs in everyday places. The level of hearing loss, noise in the environment, and distance the child is from meaningful communication or sound all interact to determine the size of the barrier that the hearing loss imposes on development of communication skills. Refer to the SHINE Early Listening Function Questionnaire for more insights into determining the size of a child's "listening bubble".
Hearing thresholds determined through audiological evaluation define the degree of hearing loss. The following paragraphs provide pertinent information on persons with mild to profound hearing loss.
Persons with mild or unilateral hearing loss (occurring in only one ear) will have difficulty perceiving speech in a clearly understandable manner at a distance greater than 6 feet. In the presence of noise, they will have inconsistent perception of language and may miss important social cues when no amplification is used.
Persons with a moderate degree of hearing loss are unable to hear when conversations occur at typical distances (6 – 8 feet) but will respond to some sounds that occur at close distances when no amplification is used.
Persons with a severe degree of hearing loss will not perceive speech sounds unless amplification is used, and may not hear all speech sounds depending on their ability to hear across the frequency (pitch) range. Even with amplification, speech sounds may be perceived as substantially quieter than what is experienced by persons with normal hearing. It is important to remember that you need to be relatively close to the person when speaking.
Persons with profound degrees of hearing loss will not be able to perceive a substantial portion of the speech signal even when amplification is used. Learning language through hearing alone with a profound hearing loss can be compared to figuring out a picture puzzle with most of the pieces missing. This is why visual forms of communication or cochlear implantation is considered as a viable means to augment whatever small amount the child is able to perceive auditorially.
Ear infection, fluid behind the eardrum or a structural problem with the formation of the outer ear or bones of the middle ear will cause some level of blockage of sound so that it will not be conducted effectively into the inner ear. Hearing loss caused by these types of blockages is called a conductive hearing loss.
Most of the hearing loss considered 'permanent' is due to missing, deformed, or damaged hair cells in the inner ear. The inner ear is considered the sensory organ of hearing. When a signal created by a sound is conducted into the inner ear, the hair cells bend and a very small electrical signal is sent up the auditory nerve to the brain. Any problem in hearing that is caused by the hair cells not delivering these signals to the brain is called a sensorineural hearing loss.
A person can have a blockage in the outer or middle ear causing a conductive hearing loss that occurs at the same time as they have a problem with the hair cells sending signals to the brain causing a sensorineural hearing loss. In this situation the person is said to have a mixed hearing loss.
There are a small number of persons who have normal structures in the outer, middle and inner ear but who have difficulty processing sound when it reaches the brain. This could be compared to having a radio on, but tuned improperly to a radio station so that varying degrees of static are heard along with the music or speech. This is caused by certain nerve cells in the brain not firing in a synchronized manner to bring the sound signal intact to the portion of the brain that can process it for meaning. These persons are said to have auditory dyssynchrony. Persons with auditory dyssynchrony typically receive limited benefit from amplification because hearing aids make sound louder but they do not assist in ‘tuning the radio station' part of the problem. Cochlear implants have resulted in some success in improving the sound processing ability of persons with auditory dyssynchrony. Auditory dyssynchrony can occur in a wide range of impairments and may be present to some degree when sensorineural hearing loss also occurs. In these cases, amplification may provide some degree of benefit.
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