BACKGROUND: Researchers at Wake Forest Baptist Medical Center are developing a Bone-Anchored Hearing Aid (BAHA).
HOW IT WORKS: If you strike a tuning fork and hold the base of it against your teeth, you will be able to hear the tone just as clearly as you would were you holding it up next to your ear. This same principle is making it possible for patients with serious hearing problems in the outer and middle ear to hear perfectly through the cochlea in the inner ear. The BAHA is attached to a small post, which is surgically anchored to the skull behind the ear. The BAHA converts sound into vibrations that are transmitted to the skull, and thus, the cochlea, allowing the patient to hear. The BAHA works differently than cochlear implants, which simulate hearing by picking up sound through an external microphone located behind the ear and transmitting sound as electrical signals across the skin to an implanted receiver. A cochlear implant sends microcurrents directly into the auditory nerve, producing the sensation of hearing in the brain.
HEAR, HEAR: Our ears detect sound as vibrations in the air. Those sound waves cause the eardrum to vibrate, sending waves through a fluid inside the cochlea This in turn causes tiny hairs -- each tuned to the different pitches of the sound -- to vibrate as well, stimulating nerves which send electrical signals to the rain for processing. Having two ears makes it possible to determine from where a sound is coming. Time lag and differences in volume provide useful clues. For instance, sound coming from one direction will reach the ear furthest away about 1/500 second later than the closer ear, and the brain can detect this time lag. A difference in volume between the two ears depends on the frequency of the sounds. It is easier for us to tell the direction of high frequency sounds better than low frequency sounds, because the higher frequencies are more easily blocked by the hear, and therefore do not easily reach the far ear.
ABOUT HEARING LOSS: Loud sounds stress and potentially damage the delicate hair cells in the inner ear that convert mechanical vibrations (sound) into the electrical signals that the brain interprets as sound. Over time, the hair cells can become permanently damaged and no longer work, producing hearing loss. Noise-induced hearing loss can be caused by two types of noise: sudden busts, such as firearms or fireworks, or continuous exposure to loud noise, such as motorized recreational vehicles, loud sporting events, power tools, farming equipment, or amplified music. For the latter, it depends on the level and duration of the noise exposure. It takes repeated exposures over many years to cause a gradual onset of noise-induced hearing loss in both children and adults.