In a University of Maryland lab, psychologist Robert Dooling trains hundreds of small, colorful parakeets, zebra finches, and canaries to chirp on command. In about three weeks, the birds learn to mimic computer-produced sounds. Once the birds' vocalizations match the template, Dooling, who heads the university's comparative psychoacoustics laboratory, rewards them with seed.

Dooling isn't interested in producing sweet songs, but rather in understanding what happens when these little creatures lose their hearing. The birds are then exposed to noise, which damages the thousands of hair cells, or sensory cells, located in the inner ear. When undamaged, these cells transmit sound through nerves to the brain. When injured, the birds become deaf and lose their ability to chirp precisely.

Dooling and his partner, Brenda Ryals at James Madison University, want to learn if hearing and speech return to normal levels once the hair cells regrow. According to their tests, birds...

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