| Visitors are invited to
demonstrate the usefulness of binocular depth perception by trying
to thread a needle with only one eye. They can "thread"
the giant needle in the exhibit with a long metal rod held about
at arm's length. Most people don't even come close when they first
try it with one eye. After several attempts, however, they begin
to get closer and closer to the target. People who have no stereoscopic
vision learn to use other clues in place of two eyes.