LITTLE ROCK — An abbreviated refresher on how you hear:
Sound waves are produced when things - from leaves to lightning - vibrate in matter. Though we think of air as the ideal medium, children are often amazed at how near a waterproof watch alarm sounds from the other end of a swimming pool.
The human ear is sensitive to a band of sound frequencies (the rate of sound waves) that begins at 20 hertz (whale song) to 20,000 hertz (a dog whistle). Of course, frequencies extend far beyond human perception. Bats can hear frequencies exceeding 100,000 hertz, and dolphins as high as 200,000 hertz.
Vibration creates waves of compressed air particles that cause the eardrum to quiver. The vibrating drum is picked up and parsed by the hammer, anvil and stirrup - if you’re disinclined to Old West imagery, the malleus, incus and stapes - which hear low, midrange and high pitches, respectively. These send more vibrations through the fluid cavity of the inner ear to the cochlea, wherein thousands of microscopic hairs flex and bend with the fluid waves. These hairs trigger nerve impulses that are picked up by the brain.
Most hearing loss is the withering and deadening of these hairs inside the cochlea, and the longest, most nimble and vulnerable of these are receptive to higher frequencies. Thus, when our hearing is damaged, we retain sensitivity to low frequencies but lose higher ones. So the first to go are your wind chimes, your grandchildren’s air kisses, your Rush albums.
Style, Pages 32 on 06/22/2010