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In this photo taken Oct. 16, 2012, Austin Benavidez, who is blind, practices his tennis serve using an oversized ball filled with ball bearings at the California School for the Blind in Fremont, Calif. Students at the school are learning to play tennis, and expanding the boundaries of what the blind can do while offering new insights into the human mind. They must turn their ears into eyes, listening for the ball's bounce to figure out where to swing their rackets. (AP Photo/Ben Margot)

Sound guides blind tennis players

The state-supported campus in Fremont is one of three American schools

for the blind that recently began teaching adapted tennis, which was

invented in Japan in the 1980s. A nonprofit group called Tennis Serves is working to promote the sport throughout the U.S. Players use a foam ball filled with metal beads that rattle on impact,

allowing them to locate the ball when it hits the ground or racket. Once

served, they have to return the ball before it bounces three times.