Taylor Made: Good vibrations II
As with most human conditions, deafness has a spectrum. To be “deaf” can mean a little hard of hearing, or unable to hear anything at all, or somewhere in between. It is easy to forget that, even in the extreme case, a deaf person can still experience sound. Even if a person’s ear cannot detect vibrations transmitted through air, those same vibrations can be experienced in other ways.
Often when one sense is suppressed, the sensitivity of the other senses heightens to compensate. For example, many blind people have a better-developed sense of hearing than sighted people because they rely more on their hearing to perceive the world around them. In similar form, deaf people are commonly more sensitive to vibrations. At concerts or other places where music is being projected at higher volume, some people might hold a plastic cup of water, balloon, or other item that more efficiently transmits vibrations. In this manner, they can feel the sound waves in their hands as the object vibrates. Sometimes these vibrations can also be felt through the floor, or even through the body itself, such as the hair or in the gut. Many different methods have reported been reported for experiencing sound, especially music.
The part of the ear that everyone is most familiar with is the external part—a cartilaginous, sound-gathering device also known as the auricle. The curves in the auricle are actually designed not only to help us determine where sound waves are coming from, but also to emphasize the specific frequencies that most often occur in human speech. Beyond the auricle is the ear canal, which feeds sound to the eardrum. When the eardrum vibrates, it activates the middle ear bones. These bones transfer energy to the inner ear bones. The malleus and incus form a sort of linkage system by which they are able to operate the stapes, which presses against the cochlea, causing waves to propagate through its liquid. Because of the leverage produced by the linkage system and the difference in surface area between the eardrum and stapes, the final pressure felt by the inner ear is said to be 22 times greater than that of the sound that entered the ear canal.
As the vibrational waves move through chambers in the cochlea, they pass over tiny hairs. Each section of hair has a different resonant frequency and will only vibrate when the correct frequency passes. The brain reads these vibrations through the auditory nerve. The system itself is pretty efficient, but with each moving part comes the possibility of failure.
Conductive hearing loss is caused by a physical blockage between the ear canal and inner ear. This could be fluid build-up from a cold (Have you ever had an ear infection that affected your hearing?), abnormal bone growth, excessive earwax—the list goes on. Sensorineural hearing loss, caused by malfunctions in the hairs within the cochlea, is most common. Some people experience a mix of these two types, where factors from both are present, while others still have what’s called auditory neuropathy—the ear functions normally, but signals are not correctly transmitted to the brain. This type of hearing loss stems from neurological conditions or conditions experienced at birth, such as jaundice. Each of these can be offset with assistive technologies, the most commonly known of which are hearing aides.
Some research today focuses on bringing a more total-body experience to music, for deaf and hearing people alike. One idea currently being developed is to wear a harnessed apparatus that transmits vibrations from music to various areas of the body. If you’re curious about feeling vibrations without audible sound, try blocking out background noise using earplugs or noise cancelling headphones or earmuffs, then placing your hand against something that gently vibrates, such as a kitchen appliance or the hood of a car with the engine running. Separating the physical and auditory sensations of sound waves can be a striking experience in and of itself.
For more on sound, see my earlier blog Faking the sound of bells