Sight without light 

Most people would likely agree that humans cannot see in total darkness. But spelunkers, people who study and explore caves, have made anecdotal observations for years disputing that assumption. And they may now have data on their side.

A new University of Rochester study shows that some people have the ability to see their own bodies move in total darkness.

Through a series of experiments involving more than 100 subjects, Duje Tadin, a professor of brain and cognitive sciences at the UR, and Kevin Dieter, a post-doctoral fellow at Vanderbilt University, found that roughly 50 percent of people can see their hands move in total darkness. Their findings were recently reported in the journal Psychological Science.

In one of the most revealing experiments, the researchers used a computerized eye-tracking device, says Tadin, because eye movements don't occur randomly; the eyes need to lock on to something and track it.

Roughly half of the subjects outfitted with the device and with goggles that prevent light transmission saw their hands moving, Tadin says.

Since the subjects did not see the researchers' hand movements, he says, the study suggests that a person's own body movements could signal some form of brain activity that produces a visual image even in the absence of light.

The researchers also found that synesthetes, people who are known to see numbers and letters in color or other combinations of sense-blending, possessed the ability to see their hand movements in darkness, too.

Tadin says that the experiments may show that not only is the brain extremely involved in people's sight perceptions, but that our senses work together more than previously realized. Future research could lead to improving hand coordination among the elderly and disabled, he says.