Auditory System

Hearing is a complex process of picking up sound from the ear and become meaningful by the coordination between auditory nerve and brain's auditory processing centers. The human ear consists of three sections: the outer ear, the middle ear, and the inner ear. The outer ear includes the visible part of the ear (pinna) and the external auditory canal. The middle ear is an air-filled space separated from the outer ear by the eardrum. The middle ear contains Eustachian tube and three small bones (called malleus, incus and stapes), which constitute the ossicular chain. These bones connect the eardrum to the inner ear. The most important feature of inner ear responsible for hearing is the cochlea. In addition, the semicircular canal of inner ear is responsible for balance. Both of them are full of fluid and have thousands of tiny nerve fibers.

What is Hearing Loss?

Many diseases can affect the hearing of children and adults. There are two types of hearing loss: congenital or acquired. If a hearing loss is congenital, it is present at birth, associated with the birth process, or to have developed in the first few days of life. In contrast, acquired hearing loss represent the hearing disability has not present at birth but developed later, either during childhood or adulthood.

Hearing loss can also be classified as either pre-lingual or post-lingual. A preolingual hearing loss occurs before the acquisition of language and speech. A post-lingual hearing loss is one occurring after developing a first language.

The hearing level (HL) is a quantified measure of “normal” hearing in decibels (dB). A decrease in hearing sensitivity is indicated by larger values of hearing level, thus higher dB indicating worse hearing ability. Normal human ear can respond to sounds that are very faint (i.e. less that 25 dB (HL)). Otherwise, the patient should suffer from hearing loss. Degree of hearing loss refers to the severity of the loss. There are typically five broad categories. The numbers are representative of the patient's softest intensity that sound is perceived.