50 percent of people can see the movement of their own hand in the dark, researchers say

50 percent of people can see the movement of their own hand in the dark, researchers say

The researchers discovered that the ability to see in the dark offers clues to how the brain deals with sensory information.

According to a news release from Vanderbilt University, your brain can “see” in the dark. Using computerized eye trackers, researchers found that at least 50 percent of people can see the activity of their own hand even in the dark.

“Seeing in total darkness? According to the current understanding of natural vision, that just doesn’t happen,” noted Duje Tadin, a professor of brain and cognitive sciences at the University of Rochester, in a statement. “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.”

The researchers discovered that the ability to see in the dark offers clues to how the brain deals with sensory information.

“Any time you willfully execute a movement—such as waving your hand in front of your face—your brain generates command signals sent to the muscles causing them to produce the movement. Having issued those motor orders, the brain also expects them to be carried out, and that expectation is signaled to other parts of the brain as a heads-up that something is about to happen,” posited co-author Randolph Blake, Centennial Professor of Psychology at Vanderbilt University. “We surmise that those heads-up signals find their way into the visual pathways, thus producing an illusory impression of what would ordinarily be seen—a kind of self-fulfilling prophecy.”

According to the researchers, the ability to see self-motion in the dark is likely learned. “Our brains learn to predict the expected moving image even without actual visual input,” Vanderbilt postdoctoral researcher Kevin Dieter.

The researchers created several experimental setups and found that about 50 percent of participants detected the motion of their own hand and they did so consistently, despite the assumptions formed by wearing a mask that appeared to have small holes and one without “holes.” Only a few participants observed activity when the experimenter moved his hand, highlighting the significance of self-motion in this visual experience. As determined by the eye tracker, participants who reported observing activity were also able to easily track the activity of their hand in the dark more accurately than those who reported no visual sensation.

Reports of the strength of visual images differed greatly among participants, but synesthetes (people who experience a blending of their senses in daily life) were much better at not just observing activity, but also experiencing distinct visual form.

The study’s results are described in greater detail in the journal Psychological Science.

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