How We Hear

When sound enters your ear, it consists of airwaves of many different frequencies. These multiple-frequency waves enter your ear canal and strike the ear drum (tympanum), which transmits the waves via three small bones attached to it (ossicles) to a spiral-shell-shaped, fluidfilled chamber called the cochlea. This chamber is lined with tiny hair cells (cilia), which vibrate back and forth within the fluid in synchrony with the frequencies of the airwaves that entered your ear. Some of the cilia vibrate in response to low-frequency waves, others to higher and higher frequencies. They convert the original sound waves to electrical impulses that travel along the auditory nerve to the brain.

Over time, many of the cilia die or become damaged due to aging, disease, and/or exposure to high-intensity noise. Typically the cilia that transmit higher-frequency waves are the most susceptible to damage, so that most people show hearing loss at the higher frequencies of sound. When your hearing is tested, the audiologist measures how well you hear sounds of all different frequencies along the sound spectrum and makes an audiogram, a graph showing the frequencies at which you hear normally and those at which you show a loss in hearing ability. The two charts below demonstrate what a normal audiogram looks like and what an audiogram showing hearing loss looks like. Note how the line drops off at the right of the graph in the abnormal audiogram, showing increasing hearing loss at higher and higher frequencies.