Hearing impairment is the decreased ability to hear and discriminate among sounds. It is one of the most common birth defects. Each year in the United States, about 12,000 babies (3 in 1,000) are born with significant hearing impairment (1). Hearing impairment that is present at birth is called congenital hearing impairment. Hearing impairment also can develop later in childhood or during adulthood.

Normal hearing thresholds are not the same for all frequencies in any species of animal. If different frequencies of sound are played at the same amplitude, some will be loud, and others quiet or even completely inaudible. Generally, if the gain or amplitude is increased, a sound is more likely to be perceived. Ordinarily, when animals use sound to communicate, hearing in that type of animal is most sensitive for the frequencies produced by calls, or, in the case of humans, speech. This tuning of hearing exists at many levels of the auditory system, all the way from the physical characteristics of the ear to the nerves and tracts that convey the nerve impulses of the auditory portion of the brain.

It can be caused by many physical conditions (e.g., childhood illnesses, pregnancy-related illnesses, injury, heredity, age, excessive or prolonged exposure to noise), and result in varying degrees of hearing loss. Generally, hearing impairments are categorized as mild, moderate, severe, or profound. An individual with a moderate hearing impairment may be able to hear sound, but have difficulty distinguishing specific speech patterns in a conversation. Individuals with a profound hearing impairment may not be able to hear sounds at all.

Hearing impaired student shows an ever increasing gap in vocabulary growth, complex sentence comprehension and construction, and in concept formation as compared to students with normal hearing. Hearing impaired students often learn to "feign" comprehension with the end result being that the student does have optimal learning opportunities. Therefore, facilitative strategies for hearing impaired students are primarily concerned with various aspects of communication. Other problems arise because deafness is an invisible disability.

Syndromes deafness accounts for the other cases of genetic deafness. Some syndromes have a particular inheritance pattern (eg, autosomal dominant for Gernet syndrome, autosomal recessive for Winter syndrome, X linked for Rosenberg syndrome). Others are sporadic (eg, cat-eye, Turner, or Klinefelter syndrome). Physical findings usually indicate the presence of a syndrome; however, children with some syndromes develop the associated physical findings late in childhood.

The ear consists of three parts - the outer ear, the middle ear and the inner ear. The outer ear is made up of the visible part of the ear on the side of your head, the ear canals that go into your head, and the eardrum, a thin layer of tissue that Sep rates. It is easy for teachers to "forget about it" and treat the student as not having a disability. It has also been shown that hearing impaired students with good English skills also have good science concept formation.

Hearing loss can be inherited. Both dominant gene and recessive genes exist which can cause mild to profound impairment. If a family has a dominant gene for deafness it will persist across generations because it will manifest itself in the offspring even if it is inherited from only one parent. If a family had genetic hearing impairment caused by a recessive gene it will not always be apparent as it will have to be passed onto offspring from both parents.


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Autor: peterhutch

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