Hearing Impairment

Definition of Hearing Impairment

Hearing plays an important role in development and daily performance. Hearing impairment occurs when there's a problem with, or damage to, one or more parts of the hearing mechanism.

Types of Hearing Impairment

Hearing impairment can be classified into four categories depending on the site of the problem in the ear: conductive, sensorineural, mixed, and central auditory processing disorder:

• Conductive hearing loss: a conductive hearing impairment results from blockage or damage to the outer or middle ear structures. This problem interferes with the transmission of sound through the outer and middle ear to the inner ear, resulting in reduced loudness of the sound. Conductive hearing loss can fluctuate according to the presence or severity of the blockage.
• Sensorineural hearing loss: sensorineural hearing loss results from damage to the inner ear or the auditory nerve. Sensorineural hearing loss can range from mild to profound, and often affects the individual's ability to hear certain frequencies more than others. Thus, even with amplification to increase the sound level, the individual with sensorineural hearing loss may perceive distorted speech sounds, resulting in difficulty with understanding speech and interpreting various sounds (quantity and quality of sound). 
• Mixed hearing loss: mixed hearing loss refers to a combination of conductive and sensorineural hearing loss, indicating that there may be damage in the outer or middle ear and the cochlea or auditory nerve.   
• Central auditory processing disorder: this form of hearing impairment occurs when the auditory centers of the brain are affected by injury, disease, tumor, heredity, birth trauma, head trauma, or unknown causes. Although the outer, middle, and inner parts of the ear deliver sound signals, these signals are unable to be processed and interpreted by the brain. Thus, even though the person’s hearing may be normal, there are difficulties with understanding what is being said, resulting in learning problems.

Causes of Hearing Impairment

Causes for conductive hearing impairment include excessive earwax (cerumen); middle ear infections (such as otitis media, when pus, fluid build-up or inflammation causes pain and reduces the ability of the eardrum to vibrate); a hole or perforation of the ear drum and otosclerosis (the eardrum and the ossicles have decreased mobility). In many cases, a conductive hearing impairment can be corrected with medication, hearing aids, or surgery.

Causes for sensorineural hearing loss include genetic disorders (which can interfere with proper development of inner ear structures); injuries; complications during pregnancy or birth; infections or illnesses (such as mumps, measles, chickenpox) and medication side effects.

Causes for mixed hearing loss include damage in the outer or middle ear and the cochlea or auditory nerve. 

Causes of central auditory processing disorder may be genetic, a brain injury, diseases and repeated middle ear infections.

Symptoms for Hearing Impairment

Possible signs of a hearing impairment include:

• Lack of, or delayed development of, speech and language.
• Not responding when addressed.
• Difficulty with following directions or instructions.
• Seeming distracted and/or confused.
• Turning head to position ear in the direction of the speaker.
• Favouring one ear over another.
• Using a loud voice when speaking.
• Mispronouncing words (such as misarticulation of certain speech sounds or omitting certain consonant sounds).
• Asking for information to be repeated frequently.
• Appearing to be inattentive, restless, tired, or daydreaming
• Getting distracted easily by visual or auditory stimuli.
• Intently watching faces during conversation.
• Giving incorrect answers to questions.
• Not being startled by loud noises.
• Preferring to be by themselves (i.e., playing alone rather than with a group, or withdrawing from social situations).
• Problems hearing environmental sounds (i.e. doorbell, telephone ringing, people calling).
• Sitting close to the sound source (e.g. TV, radio, and/or turning up the volume).