At least 50 per cent of people can see the movement of their own hand even when it is pitch dark, a new study, that used computerised eye-trackers, has found.
Even in the absence of all light, the brain keeps track of the body, researchers said. Neuroscientists and psychologists discovered that the mind continues to perceive motion in complete darkness. Their findings suggest that 50 per cent of the population sees in the dark without realising it.
"Seeing in total darkness? According to the current understanding of natural vision, that just doesn't happen," says Duje Tadin, a professor of brain and cognitive sciences at the University of Rochester who led the investigation.
"But this research shows that our own movements transmit sensory signals that also can create real visual perceptions in the brain, even in the complete absence of optical input," said Tadin.
Through five separate experiments involving 129 individuals, the authors found that this eerie ability to see our hand in the dark suggests that our brain combines information from different senses to create our perceptions.
The ability also "underscores that what we normally perceive of as sight is really as much a function of our brains as our eyes," said first author Kevin Dieter, a post-doctoral fellow in psychology at Vanderbilt University.
For most people, this ability to see self-motion in darkness probably is learned, the authors conclude. "We get such reliable exposure to the sight of our own hand moving that our brains learn to predict the expected moving image even without actual visual input," said Dieter. The study was published in journal Psychological Science.