Types of Hearing Loss

Hearing loss is categorized by what portion of the auditory system is damaged. There are three basic types of hearing loss: sensorineural, conductive and mixed hearing loss. There is also a fourth, less common, type referred to as a central hearing loss.

Sensorineural Hearing Loss

In sensorineural hearing loss, the damage lies in the inner ear, the acoustic nerve, or both. Most physicians call this condition "nerve deafness." Sensorineural hearing loss is the most common type of hearing loss affecting the adult population and is characterized by a loss of volume as well as a decrease in hearing clarity.

The cochlea (the hearing organ), has approximately 30,000 hearing nerve endings (hair cells). These hair cells, and the nerve that connects them to the brain, are susceptible to damage from a variety of causes such as aging and noise exposure.

The term "sensory" hearing loss is applied when the damage is in the inner ear. Common synonyms are "cochlear" or "inner-ear" hearing loss.

"Neural" hearing loss is the correct term to use when the damage is in the acoustic nerve, anywhere between its fibers at the base of the hair cells and the relay stations in the brain. Other common names for this type of loss are "nerve deafness" and "retrocochlear" hearing loss.

Conductive Hearing Loss

Conductive hearing loss is due to any condition that interferes with the transmission of sound through the outer and middle ear. Conductive hearing losses cause sound waves not to be transmitted effectively to the inner ear because of some interference in:

• The external ear canal
• The mobility of the eardrum
• The three tiny bones inside the middle ear
• The middle-ear cavity
• The openings into the inner ear
• The eustachian tube (the tube that connects the middle ear to the back of the throat)

Modern techniques make it possible to cure or at least improve the vast majority of cases involving problems with the outer or middle ear. Even if people with conductive hearing loss cannot be treated medically or surgically, in most cases hearing aids are very effective. This is because conductive losses are characterized primarily by a loss of volume.

Mixed Hearing Loss

The term Mixed Hearing Loss is used to describe a hearing loss in which there are both conductive and sensorineural components present. That is, there is a disruption in the transmission of sound through the outer and middle ear as well as damage to the hair cells in the inner ear.

Central Hearing Loss

In central hearing loss, the problem lies in the central nervous system, at some point within the brain. Interpreting speech is a complex task. Some people can hear perfectly well but have trouble interpreting or understanding spoken language. Although information about central hearing loss is accumulating, it remains somewhat a mystery in otology (the medical specialty of ear medicine and surgery).

A condition called Central Auditory Processing Disorder (CAPD) frequently leads people to think they have hearing loss when their hearing is actually normal. Basically, the problem involves a person's inability to process complex auditory signals. People with central auditory processing disorders often have difficulties that include:

Problems "hearing" when there are several conversations going on

Inability to read or study with the radio or television on

Problems reading if someone turns on a vacuum cleaner or air conditioner near them

Generally missing the first sentence from people talking to them if they are involved in an auditory attention task (such as watching television)

Although such people (as well as their families and friends) frequently suspect that they have a hearing loss, the function of the ears is usually found to be normal with routine hearing tests. In these cases a comprehensive diagnostic battery of auditory processing tests is necessary to identify this disorder. Research has shown auditory training and the use of FM systems to be helpful in the treatment of CAPD.

References:

• http://www.seattlehear.com/links.htm
• http://www.prohear.net/professional-hearing-services-aid-sales
• http://www.asha.org/public/hearing/anatomy/