You've seen the graph since you took Science class in primary school: The electromagnetic spectrum comprised of a tiny-winy slice of visible light, with ultraviolet and X-rays at the top, and infrared at the bottom. And ever since, our teachers have taught us that human beings are incapable of seeing both the infrared or ultraviolet radiation, without the aid of special equipment. Right?
WRONG.
Turns out a new experiment has demonstrated that, under a special set of circumstances, the human retina CAN perceive electromagnetic wavelengths at the infrared spectrum. The study was carried out by an international team of researchers co-led by scientists at the Washington University School of Medicine in St. Louis, and their paper was published on Dec. 1, in the Proceedings of the National Academy of Sciences (PNAS) Online Early Edition.
Using retina cells of both mice and humans, and powerful lasers that emit pulses of infrared light, the researchers found that when the laser was pulsed at rapidly-enough intervals, the light-sensing cells in the retina would get a "double whammy" of energy. When that happens, the eye would be able to detect the light, even though is actually below the range of the standard visible spectrum.
"We're using what we learned in these experiments to try to develop a new tool that would allow physicians to not only examine the eye but also to stimulate specific parts of the retina to determine whether it's functioning properly," said senior investigator Vladimir J. Kefalov, PhD, associate professor of ophthalmology and visual sciences at Washington University. "We hope that ultimately this discovery will have some very practical applications."
What originated the experiments was something of an odd 'glitch' in another investigation conducted by the research team, in which the team members reported seeing occasional green flashes when working with the infrared laser. Intrigued by the apparent impossibility of such visions, the scientists moved on in trying to solve the mystery.
"They were able to see the laser light, which was outside of the normal visible range, and we really wanted to figure out how they were able to sense light that was supposed to be invisible," said Frans Vinberg, PhD, one of the study's lead authors and a postdoctoral research associate in the Department of Ophthalmology and Visual Sciences at Washington University.
After consulting the scientific literature, as well as previous reports of people claiming to see in infrared, the team started to conduct trial-and-error experiments, and they eventually discovered that the shorter the pulse, the more likely is a person to perceive it. By packing more photons in the energy pulse makes it more possible that two photons with a wavelength of a 1000 nm (nanometers), would be perceived as a single photon of 500 nm, which falls into the range of visible light (between 400-720 nm).
What appeals to me about this study is not its potential applications in Medicine or industry –or the fact that the scientists didn’t follow the “it can’t be/therefore it isn’t” of skeptics, which helped them uncover a new property of Nature– but whether it could somehow play a factor in certain 'paranormal events'. Would it be possible that some 'ghostly' apparitions are the result of the witness' retina being excited by electromagnetic energy that, under certain circumstances, might be perceived as visible light? 
I'm also reminded of John Keel's ideas about what he coined as the ‘Superspectrum‘, because he was convinced that all paranormal phenomena –from ghosts to UFOs– had essentially an electromagnetic nature. Also, think of all the reports of flashing lights illuminating UFOs like Xmas trees; not the best approach to go unnoticed –or is it?
Maybe it's possible that individuals who are more sensitive than the average, sometimes perceive manifestations that normally go unseen by the naked eye.
In any case, it's cool to think that my old 4th-grade Science book is now outdated. Now if you'll excuse me, I'm in the middle of my attempt to acquire supervision thanks to the Science for the Masses vitamin supplements. ___________________________________________
- Phis-Org: The human eye can see 'invisible' infrared light.
- The Eighth Tower: On Ultraterrestrials and the Superspectrum, by John A. Keel [Amazon US & UK]
[H/T The Anomalist]
