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Hearing Impairment

How do we hear?

  • Hearing loss is one of the most common health handicapping conditions among children and adults. The hearing sense is the cornerstone upon which our unique human communication system is built.
  • This hearing handicap therefore makes it very difficult for people to learn to speak a language, which impairs their ability to communicate naturally with other people. It also has a detrimental effect on personality and emotional development.

 

 

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Hearing screening

Tests provide a quick and cost effective way to separate people into two groups: a pass group and a fail group.hearing_child

  • Hearing screening occurs from birth throughout the adult years

Newborns and Infants:

Screening Techniques :

  • Screening procedures for newborns and infants can detect permanent or fluctuating, bilateral or unilateral, and sensory or conductive hearing loss,
  • The screening of newborns and infants involves use of non-invasive, objective physiologic measures :
  • Otoacoustic emissions (OAEs) and/or
  • Auditory brainstem response (ABR).
  • Both procedures can be done painlessly while the infant is resting quietly.

Otoacoustic emissions are inaudible sounds from the cochlea when audible sound stimulates the cochlea. The outer hair cells of the cochlea vibrate, and the vibration produces an inaudible sound that echoes back into the middle ear. This sound can be measured with a small probe inserted into the ear canal. Persons with normal hearing produce emissions. Those with hearing loss greater than 25-30 dB do not. OAEs can detect blockage in the outer ear canal, middle ear fluid, and damage to the outer hair cells in the cochlea.

Auditory brainstem response is an auditory evoked potential that originates from the auditory nerve. It is often used with babies. Electrodes are placed on the head, and brain wave activity in response to sound is recorded. ABR can detect damage to the cochlea, the auditory nerve and the auditory pathways in the stem of the brain.

 Older Infants and Toddlers

  • As some causes of hearing loss do not take effect until later in the child’s development.
  • Hence they monitored at least every 6 months until 3 years of age, and at regular intervals thereafter dependent upon the risk factor .
  • Screening procedures to detect hearing impairment that exceeds 20-30 dB HL
  • . Both of these methods are behavioral techniques that require involvement and cooperation of the child.

Visual reinforcement audiometry (VRA) is the method of choice for children between 6 months and 2 years of age. The child is trained to look toward (localize) a sound source. When the child gives a correct response, e.g., looking to a source of sound when it is presented, the child is “rewarded” through a visual reinforcement such as a toy that moves or a flashing light.

Conditioned play audiometry (CPA) can be used as the child matures. It is widely used between 2 and 3 years of age. The child is trained to perform an activity each time a sound is heard. The activity may be putting a block in a box, placing pegs in a hole, putting a ring on a cone, etc. The child is taught to wait, listen, and respond.

Preschoolers

  • Identify children most likely to have hearing loss that may interfere with communication, development, health, or future school performance..
  • Some children may pass an initial hearing screening, but still be at risk for hearing loss that fluctuates, is progressive (gets worse over time), or is acquired later in development.
  • Conditioned play audiometry (CPA) is the most commonly employed procedure.
  • Acoustic Immittance screening may include tympanometry, acoustic reflex, and static acoustic impedance.
  • Tympanometry introduces air pressure into the ear canal making the eardrum move back and forth. A special machine then measures the mobility of the eardrum. Tympanograms, or graphs, are produced which show stiffness, floppiness, or normal eardrum movement.

Type, Degree of Hearing Loss

Type of Hearing Loss

Hearing loss can be categorized by where or what part of the auditory system is damaged.

Conductive hearing loss ,

Sensorineural hearing loss and

Mixed hearing loss.

Conductive hearing loss occurs when sound is not conducted efficiently through the outer ear canal to the eardrum and the tiny bones, or ossicles, of the middle ear.

Sensorineural hearing loss occurs when there is damage to the inner ear (cochlea) or to the nerve pathways from the inner ear (retrocochlear) to the brain. Sensorineural hearing loss cannot be medically or surgically corrected. It is a permanent loss

Sometimes a conductive hearing loss occurs in combination with a sensorineural hearing loss. In other words, there may be damage in the outer or middle ear and in the inner ear (cochlea) or auditory nerve. When this occurs, the hearing loss is referred to as a mixed hearing loss.

Unilateral hearing loss (UHL) means that hearing is normal in one ear but there is hearing loss in the other ear.

Degree of Hearing Loss

Degree of hearing loss refers to the severity of the loss. The numbers are representative of the patient’s thresholds, or the softest intensity at which sound is perceived.

Degree of hearing loss Hearing loss range (dB HL)
Normal -10 to 15
Slight 16 to 25
Mild 26 to 40
Moderate 41 to 55
Moderately severe 56 to 70
Severe 71 to 90
Profound 91+

 

Source: Clark, J. G. (1981). Uses and abuses of hearing loss classification. Asha, 23, 493-500.

Central auditory system deals with the processing of auditory information as it is carried up to the brain. Central auditory processes are the auditory processes responsible for the following behaviors:

  • Sound localization and lateralization
  • Auditory discrimination (hearing the differences between different sounds)
  • Recognizing patterns of sounds
  • Time aspects of hearing (temporal aspects of audition): temporal resolution, temporal masking, temporal integration, temporal ordering
  • Reduction in auditory performance in the presence of competing acoustic signals
  • Reduction in auditory performance in the presence of degraded (less than complete) acoustic signals

 

 

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