At times, the orbiting laboratory aboard space shuttle Columbia looks more like an outer space amusement park than a serious research facility.

The crew of scientists and doctors has played catch with a ball, peered through a virtual-reality machine mounted on their heads and spun around in a rotating chair.But shuttle Commander Richard Searfoss says that while the experiments may look like fun and games, their results could provide important answers to medical questions plaguing both astronauts and earthlings.

"The thrust of this research is twofold - not only to enable astronauts to remain in space for longer durations of time off into the future . . . but we're very hopeful that in the long term, there'll be clinical benefits back on Earth," Searfoss said Sunday during an in-flight interview.

The research continues Monday with more tests of both the astronauts and its cargo of more than 2,000 mice, rats, crickets, snails and fish that are along for the two-week mission.

On Sunday, crew members participated in a ball-catching experiment in which a 1-pound ball was propelled downward into an astronaut's hand at different speeds. The test will be used to study how the central nervous system interprets new stimuli in space.

Astronauts also used a head-mounted Virtual Environment Generator to learn how astronauts use vision, inner-ear organs and pressure cues to determine their body motion while in space.

Sleep experiments also were planned during the night on crew members Richard Linnehan and Dave Williams. The tests seek to identify factors that contribute to sleep disturbances in space and on Earth, and determine the effectiveness of sleep aids such as melatonin.

Earlier Sunday, the crew completed its second set of animal dissections - removing the fetuses of nine pregnant mice so they can be examined to determine how nervous systems develops in space.

The mice experiment, one of 26 being performed on the mission, should help scientists learn whether gravity is required for normal brain development. The answer is critical in determining whether animals and humans could be born in space, enabling space colonies to be established.