The human ear is the most complex sensory organ in the human body. Yet, its complexity is not appreciated because all we can see of it is the external ear, which is used more often to keep eyeglasses from sliding down our faces and to decorate with jewelry.
The basic function of the ear is to take sound waves, which are atom-sized variations in air pressure, and eventually convert them into nerve impulses which our brain can process. To accomplish this, the ear has an extraordinarily sophisticated system encased inside the temporal bone of our skull.
Hearing loss is perhaps the most common disability in people. Yet, it’s the one that’s most likely to go without treatment for a long period, until it reaches such a degree of impairment that work or social functioning becomes a serious concern. Hearing loss, of course, can be present at any age, from birth on. It is estimated that over 33 million people in the U.S. have hearing issues requiring some form of assistance. However, only about 10-15% of that group seeks solutions for hearing loss.
Hearing problems can result from many different causes. One cause can be as minor as earwax (cerumen) blocking the ear canal. In extreme situations, hearing loss may be caused by a tumor (usually benign) on the hearing nerve. But more often than not, hearing loss can stem from many other causes, some present at birth, most occurring later in life.
Some hearing losses are preventable. The best example of preventable hearing loss is exposure to damaging sound levels. Prevention is accomplished through the use of adequate hearing protection and avoidance of situations that would potentially cause hearing loss. Years ago, occupational hearing loss was one of the most common causes of hearing difficulties. Today, the most frequent sources of damaging noise levels are societal and recreational rather than industrial. The increased noise of urban environments from heavy vehicular traffic, extremely loud music, recreational shooting of firearms, and noisy power equipment such as chain saws, leaf blowers and other power tools all contribute to preventable hearing loss.
Hearing loss that is not preventable results from changes in our health conditions, such as cardiovascular changes due to aging, inherited conditions such as familial history of hearing loss, the administration of powerful ototoxic drugs, and other traumatic events such as accidents that injure the ear.
Some types of hearing loss result from interference with delivering sound energy to the inner ear. This is usually referred to as a conductive loss and can be treated medically or surgically. Such treatments may include simply removing impacted cerumen from the ear canal, treating ear infections with medications, or surgical intervention to treat otosclerosis, a condition resulting from excessive bony growth in the middle ear.
The most common type of hearing loss is called a sensory hearing loss (incorrectly called "nerve deafness" or "nerve loss"). This type of hearing loss results from permanent damage to the inner ear, causing the loss of many of the thousands of tiny hair cells that convert sound waves into the information sent along the hearing nerve to the brain. The nerve fibers are usually intact, but there is nothing to activate them. About 85% of people with hearing loss have sensory hearing loss. While there is no medical or surgical treatment, these people can benefit from hearing devices. When the degree of hearing loss reaches the profound level, where an individual might be classified as truly deaf, a cochlear implant, a device that stimulates the hearing nerve with tiny electrical currents, is often an option. Ear surgeons install a cochlear implant and through audiological rehabilitation, implant users can often reach high levels of success.
Advanced digital hearing devices are designed specifically to address the hearing needs of the individual with sensory hearing loss. These instruments break up the sound range into multiple frequency bands to provide precise matching of the hearing device's behavior to the pattern of hearing loss. In addition, the precise amounts of amplification needed to combat hearing loss is controlled by the digital circuits in the hearing device. The goals are to enable the user to hear soft sounds that are otherwise inaudible and then adjust amplification automatically so that average conversation is clear and comfortable. The instruments will also adjust to insure that loud sounds are not over amplified and become uncomfortable and distorted.
Advanced digital hearing instruments may also incorporate directional microphones and special signal processing that reduces interference from background noise, enabling speech to be understood in noisy environments. New technologies are now available to help people with high-frequency hearing loss, a common type of loss that previously couldn’t be helped successfully without unpleasant side effects such as feelings of blocked ears and the user's own voice echoing ("occlusion effects").
Other technical advances in hearing technology enable the use of wireless communications between the devices to automatically coordinate settings between them, as well as to enable the devices to link with smartphones, cellphones, television listening adapters and personal microphones using Bluetooth® and other low power, short-range wireless communications.
The ear consists of four primary parts, as seen in the accompanying figure. The outer ear, which includes the auricle and auditory canal, acts as a sound collector to channel the waves to the ear drum. The ear drum vibrates and moves three tiny bones, called ossicles, attached to it on the other side in the middle ear space.
These ossicles amplify the movement of the ear drum. The innermost of the ossicles, the stapes or stirrup bone, transfers the vibrations to a fluid-filled space called the cochlea or inner ear. Inside this space, which is smaller than your thumb, are thousands of tiny cells called hair cells which move from the energy transmitted through the fluid. The motion of the hair cells activate nerve fibers which are attached to them. All the nerve fibers come together in a bundle, called the cochlear nerve, to enter the brain stem. This is referred to as the neural ear. Each individual nerve fiber sends impulses to the brain that encode the original acoustic signal in a way that the brain can make sense of, based on the sounds we have heard since birth. In the majority of cases, damage to or loss of the tiny hair cells in the inner ear is the most frequent cause of hearing difficulties.