50 Percent of People Can See Hands in Pitch-Black: Confirms ‘Spelunker Illusion’

50 Percent of People Can See Hands Pitch-Black: Confirms Spelunker Illusion

If you were suspended in utter darkness, and moved your hand from side to side in front of your face, would you be able to see anything at all? A new cognitive science study suggests that 50 percent of people would be able to perceive their hands moving in front of them, even in a room that is pitch-black.

The findings of the study were published in the latest issue of the Association for Psychological Science’s journal, Psychological Science, with the research led by Professor of Brain and Cognitive Sciences Duje Tadin, based at the University of Rochester in the Department of Brain and Cognitive Sciences.

Based upon current scientific understanding of mankind’s natural vision, the capacity to see in “total darkness” is a phenomenon that most thought impossible. However, according to research conducted by Tadin and colleagues, an individual’s own movements transmit sensory electrical signals that can shape visual perception within the brain; this process is said to occur in the absence of visual input from the eyes.

The Study

The researchers performed five entirely separate experimental investigations, using a population sample size of 129 subjects.

In designing the experiment, the group tried to find an objective means of ascertaining whether people were truly visualizing their own hands in front of their faces, under pitch-black conditions; the team worried that participants might provide answers that they believed the researchers wanted to hear. Therefore, they produced an experiment that could be used to assess such bias.

Working alongside Kevin Dieter, a post-doc in the field of psychology at Vanderbilt University, Tadin designed their novel research study. The team fitted their study subjects with a computerized eye tracking device and submerged them in utter darkness. Developing a series of “false expectation” experiments, the team setup three groups of participants.

One group was led to expect they would witness motion under low light intensity, due to the use of blindfolds with small apertures. Meanwhile, another group was led to think that they would see absolutely nothing, due to use of blindfolds with no apertures present. In reality, both experimental setups used blindfolds that completely blocked out all light. A third group was then incorporated, with the experimenter waving their hands in front of the line of sight of blindfolded participants.

The group also incorporated grapheme-color synesthetes. Individuals who experience synesthesia have a tendency to “blend” particular senses. This occurs when stimulation of one sensory or cognitive pathway triggers involuntary activity in another sensory or cognitive pathway. With grapheme-color synesthesia, the individuals will see numbers or letters in particular colors.

They selected their participants from various states of America, alongside a number of other countries. However, one of Rochester University’s own laboratory technicians, Lindsay Bronnenkant, by sheer coincidence, also happened to suffer from synesthesia. She remarks on her experiences, in a recent press release:

“As a child, I just assumed that everybody associated colors with letters… A is always yellow, but Y is an oranger yellow.”

Subjects able to see their hands showed smooth motion tracking

Ultimately, in half of all subjects – Bronnenkant included – motion in their own hands could be identified, on a consistent basis. Few blindfolded subjects claimed to see any motion when the experimenter was waving their own hand in front of them, showing the significance of self-motion.

The eye trackers revealed that 46 percent of people who reported seeing their own hands were more likely to demonstrate smooth motion tracking; in contrast, only 20 percent of those claiming they were unable to see anything showed smooth motion tracking.

Meanwhile, synesthetes were much better at seeing movement with “clear visual form.” Incredibly, one of the synesthesia sufferers was able to demonstrate near-perfect eye movement, tracking her hand with 95 percent accuracy.

The team theorize that people merely learn this ability to detect their own limbs, when exposed to darkness; they suggest that it is the brain’s capacity to anticipate a moving image of our hands, despite absence of optical input.

Dieter claims that the study reaffirms the brains involvement in visual processing and highlights “… what we normally perceive of as sight is really as much a function of our brains as our eyes.”

In addition, it also adds credence to what has recently been nicknamed the “spelunker illusion” – a phenomenon that derives from the anecdotal stories of spelunking adventurers, who maintain they are able to see their hands in the dark depths of the Earth.

Ultimately, the study suggests that 50 percent of all people can see in pitch-black. The researchers do not believe the ability to be hardwired, but more research is required to discount the ability as innate.

By James Fenner

Journal Source

Psychological Science Site

Rochester University Press Release

CNN Health

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