Hearing & Hearing Loss

Hearing & Hearing Loss

Sound is vibration. Sound travels as vibrations through the air. When these vibrations reach the outer ear, this is the beginning of hearing. The ear has four main parts: the outer ear, the middle ear, the inner ear, and beyond the inner ear (retro-cochlear).

Outer Ear
The outer ear consists of the external ear (pinna), the ear canal (external auditory meatus) and the ear drum (tympanic membrane). The outer ear directs sound into the ear canal and carries it to the eardrum. When these sound vibrations reach the eardrum, the eardrum begins to vibrate.

Middle Ear
The middle ear contains the three smallest bones in the body; the malleus, incus and stapes. They conduct sound through the air filled middle ear to the inner ear. These bones are known as the "ossicles" and are connected to form the "ossicular chain". The "handle" of the malleus is embedded in the ear drum while the other end is joined to the incus. The incus in turn is connected to the stapes which rocks in and out of the oval window of the cochlea of the inner ear. The oval window moves at the same vibration rate as the eardrum. The eustachian tube, which equalizes pressure between the ear and the environment, is also found in the middle ear.

Inner Ear
The inner ear, the end organ of hearing, contains both the cochlea and the vestibular system. The snail-shaped cochlea contains approximately 3,500 inner hair cells, 9,000 - 12,000 outer hair cells. These hair cells connect to approximately 24,000 nerve fibers which are essential for hearing. The rocking of the stapes in the oval window moves fluid within the cochlea causing a "shearing" action or movement of the hair cells.

The vestibular system works to keep the body balanced.

Beyond the Inner Ear (Retro-Choclear)
The "shearing" motion, stimulating the hair cells, sends impulses beyond the cochlea, to the auditory (VIIIth) nerve. The auditory nerve carries the information to the brain, via the brainstem, for decoding or giving meaning to the sound. There are auditory centers along the brainstem and in the brain which interpret the stimulus enabling the person to understand what is being heard. If these parts of the brain are badly damaged, a person may not be able to understand any sound even though the auditory nerve has transmitted it to the brain.

Types of Hearing Loss
There are four types of hearing loss: conductive, mixed, sensorineural, and retro-cochlear.

Conductive Hearing Loss
Conductive hearing loss is caused by a problem in the outer or middle ear, including eustachian tube malfunction or a defect in the ossicular chain. In most cases, conductive hearing loss affects the lower frequencies and makes it difficult for the ear to hear vowel sounds and interpret the slight differences among them. Since vowels contain the "power of speech" the person perceives speech and other sounds as being much "quieter" than normal. If the sound is loud enough, a person with a conductive hearing loss can hear and understand clearly, thereby making them a good hearing aid candidate. Conductive hearing loss can often be medically treated. If a conductive hearing loss is not treated, it can sometimes lead to permanent damage of the inner ear.

Sensorineural Hearing Loss
Sensorineural hearing loss is the most common type of hearing loss and is caused by damage to the inner ear and/or the auditory nerve. Noise exposure, diseases, certain medications and aging can destroy parts of the inner ear and cause permanent hearing loss. Once damaged, the inner ear cannot be repaired. A "cochlear implant" is available for some who have a profound hearing loss and do not gain benefit from conventional hearing aids.

With sensorineural hearing loss, the entire cochlea is seldom damaged. If a sound is loud enough, a person with inner ear damage may hear something. The undamaged parts of the cochlea transmit sound to the auditory nerve and on to the brain, however the sound may be distorted. Distortion occurs when the cochlea changes the sound in some way. Sensorineural hearing loss is also characterized by a lower tolerance to loud sounds. Sensorineural hearing loss usually affects the high frequencies the most, which impairs a persons ability to differentiate consonant sounds.

Mixed Hearing Loss
When a person has both a conductive hearing loss and a sensorineural hearing loss, it is called a mixed hearing loss. For example, if a child who has a permanent sensorineural hearing loss gets a middle ear infection, the effects of the two types of hearing loss combine to create a greater hearing loss.

Retro-Cochlear Hearing Loss
When a person has a sensorineural hearing loss, particularly a unilateral hearing loss, the problem may be beyond the inner ear, somewhere in the brainstem. An acoustic tumor may be involved and may lie on the auditory nerve, brainstem or in the brain. Surgical intervention is most often warranted. Retro-cochlear hearing loss is noted by inconsistencies on the audiogram, such as poorer speech recognition ability than the pure tones indicate, especially at loud presentation levels.

Implications of Hearing Loss

Degree of Loss	Description	Effect	Referral
0-15dB	Normal	None	None
15-25dB	Slight	May have problems in difficult listening situations (groups, noise).	Consideration of need for hearing aid and/or assistive listening devices; may need speechreading, auditory training, preferential seating; vocational evaluation and rehabilitation may be indicated.
25-40dB	Mild	"All of the above, plus"... May have problems in difficult listening situations (groups, noise, meetings). Begin to have difficulty understanding conversations on the telephone.	Frequent otologic and audiologic monitoring; consideration for hearing aid and assistive listening devices, speechreading, auditory training; preferential seating; communication strategies and living with hearing loss training; vocational evaluation and rehabilitation may be indicated.
40-65dB	Moderate	"All of the above, plus"... Quality of speech may be affected; conversation must be loud to be understood, problems following conversations in groups, on the telephone, and other complex listening situations; dependence on visual cues.	Consideration for hearing aid, assistive listening devices; speech therapy, speechreading, special considerations (seating, lighting, noise, other). Family and individual counseling may be needed to effectively cope with hearing loss. Communication strategies and living with hearing loss training; vocational evaluation and rehabilitation may be indicated.
65-90dB	Severe	"All of the above, plus"... Will not hear conversational speech or understand clearly on the telephone, may be able to identify environmental sounds, speech may deteriorate, heavy reliance on visual cues.	"All of above, plus"... Interpreting and other accommodations may be necessary. Consideration for alerting devices; family counseling may be needed to manage adjustment to hearing loss.
90dB+	Profound	May hear some loud sounds but more aware of vibration; vision primary avenue of communication; speech may deteriorate.	All of above.

Adapted from: SHHH Series #153 "Hearing Loss and Mental Health".

Members of the Hearing Healthcare Team

Audiologist:
A professional trained in all aspects of hearing and hearing loss, but is not qualified to perform any medical /surgical procedures. The audiologist understands the effects of hearing loss and how best to remediate the problems that hearing loss can cause. The audiologist has either a Master's Degree or Ph.D. and is Certified by the American Speech-Language-Hearing Association (ASHA). This certification is denoted by the three "C"s after the degree following the name (Marilyn Doe, M.A., CCC-A) Audiologists may also dispense hearing aids.

Otologist:
The medical examination of the ear is done by an Otologist, or otolaryngologist. This is a physician (M.D.) specializing in diseases of the ear, nose and throat (ENT).

Hearing Aid Dispenser:
A hearing aid dispenser sells hearing aids. No formal educational background beyond high school is required to dispense hearing aids. Most states require a license or permit for the hearing aid dealer to dispense or sell hearing aids.

VR Counselor / Team:
The VR counselor is responsible for purchasing and providing effective and efficient services for every eligible consumer. In selecting a hearing health team the counselor must work with the consumer to establish satisfactory communication and determine the success of the services. In this process, it is the counselor's responsibility to provide choice of qualified vendors to the consumer. As the VR counselor, rapport and communication with the consumer and other members of the hearing health team may well be the most critical link in the chain of events leading to successful rehabilitation.

Counselor / Psychotherapist:
The counselor/psychotherapist may provide support to a hard of hearing or late deafened person in order to allow the person to better cope with their hearing loss. Personal adjustment counseling may be included in this process along with learning specific coping strategies and communication skills to better manage the challenges of hearing loss.

Assistive Listening / Communication Device Consultant:
This person is a trained specialist who is familiar with hearing loss, knows how to communicate with hard of hearing and late deafened people. They can evaluate the work environment regarding communication and alerting problems and are knowledgeable about the devices appropriate for the accommodation of these individuals in their specific environment.

Ophthalmologist:
Good vision is critical for the hard of hearing and late deafened person who depends on visual cues for understanding conversation. and effective interaction with others. There are some genetic conditions associated with hearing loss and visual impairment that must be ruled out in order to make an appropriate evaluation and provide effective rehabilitation services.