The Human Ear Sounds Off

If your ears ring all the time, you may not be the only one who notices. Patrick Zurek of the Center for the Deaf in St. Louis has published an article in the Journal of the Acoustic Society in which he reports on cases he has studied where the ear not only receives sound, but also produces it.

Zurek first made the discovery on himself. While studying the interference effects of tones that are close in frequency within the inner ear, he placed a microphone in the canal of his right ear. When he turned on the microphone to begin the experiment, he was astonished to find that his ear was emitting sound with a frequency of 1,910 hertz (cycles per second), which is a high pitch almost three octaves above middle C. On checking, he found that he could also detect the sound in his left ear, although he had not been physically aware of the tone in his natural hearing with either ear.

Turning to the medical literature, Zurek learned that his discovery was not altogether new; he found several reports of patients whose ears emitted high-frequency acoustic signals. One remarkable account by doctors at the University Hospital in Leiden told of a 22-year-old woman whose right ear gave off tones loud enough to be heard by other people. She was not aware of the sounds, but they annoyed her sister when the two of them played the piano together.

Zurek then placed microphones in the ears of 32 volunteers and, of the 64 ears thus tested, recorded sounds from 22 of them. None of the subjects were aware that their ears were broadcasting. There was no significant pattern in age or sex of the people affected.

The human ear is an effective transducer for converting the mechanical energy of sound waves in the air into the electrical energy involved in nerve impulses, but it is a complete mystery how this process may work the other way around. The sounds appear to originate in the cochlea, the fluid-filled spiral canal of the inner ear. If this is so, it must mean that the cochlea is not passive, as had been believed, but that it is capable of vibrating continuously. How this can be possible without the subject being aware of it is difficult to comprehend.

Zurek's work was further complicated when he and a coworker turned their attention to chinchillas, which were chosen for study because their ears are similar to those of humans. On checking the ears of 22 chinchillas for audible signals, they found none. However, when they exposed the chinchillas' ears to intense noise, they found that afterward, two of them emitted acoustic signals. In one case, the sound could be heard without amplification.

But if your ears are ringing, they probably toll audibly only for you. In his studies with human subjects, Zurek had six people who complained of the problem. None of them were among those whose ears emitted sound.