A group of British, U.S. and Canadian researchers will study whether out-of-body experiences are real, as some people have claimed after surviving cardiac arrest.

In a study run by the University of Southampton's Human Consciousness Project, researchers will examine 1,500 survivors of heart attacks over three years at 25 hospitals in Europe, the U.S. and Canada to determine if the phenomenon of seeing a light at the end of the tunnel or floating above as reported by some is genuine.

To test patients, doctors will place random photographs on shelves higher than the beds in emergency and intensive care rooms, which will only be visible if the heart-attack victims are looking down, the researchers say.

The photos will be confidential and changed routinely, they say.

"Without prompting they might say, 'I saw an image,'" said Ken Spearpoint, a resuscitation nurse at Hammersmith Hospital in West London, U.K. "If they do that, we have clear evidence that they had some sort of consciousness during a procedure that by the traditional sense — by all acceptable understanding — is clinically death."

Heather Sloan, a former nurse from Southampton, believes the phenomenon is real after she suffered internal bleeding and experienced it herself.

"I looked at the bed and on the bed was me and I realized it was a bit of an 'oh boy!'" said Sloan, who added that she watched the medical staff working on her from above.

"It happened as far as I am concerned, and anyone who has had the same experience will say the same," she said.