How Hearing Works
DIFFERENT TYPES OF HEARING LOSS
Hearing loss is described by varying degrees, not percentages. Hearing loss may be mild, moderate, moderately-severe, severe, or profound, and it can vary across pitches. A person's hearing deficit is determined by a simple hearing test where the amount of volume loss you experience is compared to an average of many other adult listeners with normal auditory ability.
The volume, or intensity, of sounds you hear is measured in decibels (dB), with 0 dB being the softest whisper and 120 dB being a jet engine. The softest sounds a person can hear are called thresholds. Normal hearing thresholds for adults are considered 0 to 25 dB.
CONDUCTIVE HEARING LOSS
Conductive hearing loss occurs when there is a problem with the way sound is conducted to the inner ear and a structure called the cochlea. The problem may lie in the ear canal, eardrum (tympanic membrane), or the middle ear (ossicles and Eustachian tube). The inner ear remains unaffected in this type of hearing loss.
Symptoms of Conductive Hearing Loss
Individuals with conductive hearing loss may report:
- That sounds are muffled
- That sounds are very low or quiet
Causes of Conductive Hearing Loss
Some causes of conductive hearing loss can include:
- Outer or middle ear infections
- Complete earwax blockage
- Deterioration of the middle ear bones (ossicles)
- Otosclerosis - Fixation of the ossicles
- Perforated tympanic membrane (TM) - A hole in the eardrum
- Absence of the outer ear or middle ear structures
Conductive hearing loss may be temporary or permanent, depending on the source of the problem. Medical management can correct some cases of conductive hearing loss, while amplification may be a recommended treatment option in long-standing or permanent cases.
SENSORINEURAL HEARING LOSS
Sensorineural (sen-sor-ee-nuhral) hearing loss occurs when there is a problem with the sensory receptors of the hearing system, specifically in the cochlea of the inner ear. The majority of sensorineural hearing loss occurs as a result of an abnormality or damage to the hair cells in the cochlea. This abnormality prevents sound from being transmitted to the brain normally, which results in a hearing loss.
Symptoms of Sensorineural Hearing Loss
Individuals with sensorineural hearing loss may report:
- Muffled speech
- Ringing in the ears (tinnitus)
- Difficulty hearing in background noise
- That others do not speak clearly
Causes of Sensorineural Hearing Loss
- Congenital - These hair cells have been abnormal since birth, which is considered a congenital condition.
- Damage to hair cells - A deficit in hearing also occurs when the cells are damaged as a result of genetics, infection, drugs, trauma, or over-exposure to noise (late-onset or acquired).
- Presbycusis - Hair cells are damaged as a result of the aging process, which causes a kind of hearing loss known as presbycusis (pres-be-cue-sis).
Sensorineural hearing losses are generally permanent and may stay stable or worsen over time. Routine hearing tests are needed to monitor the hearing loss. Amplification is the most common treatment, which includes hearing aids or cochlear implants in the most severe cases.
MIXED HEARING LOSS
Mixed hearing loss occurs when a person has an existing sensorineural hearing loss in combination with a conductive hearing loss. This type of hearing deficit is considered a mix of sensorineural and conductive hearing losses, which means there is a problem in the inner ear as well as in the outer and/or middle ear.
The conductive hearing loss may be temporary or permanent, depending on the source of the problem. Mixed hearing loss can sometimes be treated with medical management, and hearing aids are a common treatment recommendation.
NEURAL HEARING LOSS
Neural hearing loss occurs when the auditory nerve that carries impulses from the cochlea to the brain is missing or abnormal. This form of hearing deficit is difficult to diagnose, as the exact location of neural hearing loss is not always evident to hearing specialists.
To treat neural hearing loss, amplification may be recommended in some cases, depending on the severity of the damage to the hearing nerve. Individuals with neural hearing loss often have difficulty understanding speech, even when it is loud enough, especially in background noise.
Causes of Neural Hearing Loss
Some causes of neural hearing loss include:
- Acoustic tumors
- In-utero exposure to certain infections
- Severe jaundice in infancy
- Low birth weight associated with premature birth