"The moment he brought his eye in subconsciously, he was like, 'Oh wow, this looks cool,' and then probably maintained the effort," Harris said.
The movie probably had the effect of training not the muscles of Bridgeman's eyes per se, Harris said, but rather "the software he used in terms of how he looked at the world."
Researchers have suggested that creating video games with three-dimensional information could be used to help children and adults with eye misalignment problems achieve improved stereo vision, McKee said.
Looking for more insights
Bridgeman's vision still isn't perfect. A few months after viewing "Hugo," he went to an optometrist in Santa Cruz who administered a test for stereo threshold, the same one Bridgeman had taken at Berkeley in the 1980s. The test showed his stereo vision had improved dramatically since his earlier test, but still wasn't within normal range.
There still remain many unanswered questions. Just how common is it for an adult to acquire stereo vision? Which specific visual anomalies might respond best to watching a 3-D movie? Bridgeman wants to know.
He's in touch with Dennis Levi at the University of California, Berkeley, who led a study of five adults who went from being stereo-blind to seeing depth again through training.
Since a BBC article appeared about Bridgeman last year, he's gotten numerous e-mails from others with stereo vision problems. One man told him he had an experience similar to Bridgeman's.
"When it happens, it's very sudden and pleasant, to see things in 3-D that have been flat for all your life," Bridgeman said.
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