What's Really Happening When We See 'Stars' After Rubbing Our Eyes?

Photo illustration by Mental Floss. Images: iStock.
Photo illustration by Mental Floss. Images: iStock.

It's likely happened to you before: You start rubbing your eyes and almost immediately begin seeing colors, specks, and swirls from behind your closed lids. So what's happening when you see these 2001-esque "stars"? Do they only occur upon rubbing? Does everyone experience them?

Before we can get to what causes the lights, we need to understand a bit about how the eyes work. Angie Wen, a cornea surgeon at New York Eye and Ear Infirmary of Mount Sinai, tells Mental Floss that the retina—the innermost layer of the eye—consists of millions of cells, or photoreceptors. These cells, she says, "are responsible for receiving information from the outside world and converting them to electrical impulses that are transmitted to the brain by the optic nerve. Then, the brain interprets them as images representing the world around us."

However, what we see doesn't just stop there. Sometimes "we see light that actually comes from inside our eyes or from electric stimulation of the brain rather than from the outside world," Wen says. "These bursts of seemingly random intense and colorful lights are called phosphenes, and appear due to electrical discharges from the cells inside our eyes that are a normal part of cellular function."

People have been writing and theorizing about phosphenes for thousands of years. Greek philosophers thought the bursts of light were the result of fire inside our heads: "The eye obviously has fire within it, for when the eye is struck fire flashes out," wrote Alcmaeon of Croton (6th–5th century BCE), a philosopher and early neuroscientist, of the swirls and specks someone sees after getting a blow to the head. A century later, Plato—who believed that a "visual current" [PDF] streamed out of the eye—wrote that "Such fire as has the property, not of burning, but of yielding a gentle light they [the Gods] contrived should become the proper body of each day."

Plato's take was still the dominant one through the Middle Ages. Eventually, Newton (1642–1727) theorized a concept that's more in line with what's believed today about these strange sparkly visions: The phenomenon is due to light that's produced and observed when pressure and motion is placed on the eyes.

Eleonora Lad, an associate professor of ophthalmology at Duke University Medical Center who has a background in neuroscience, explains exactly why eye rubbing generates these visions: "Most vision researchers believe that phosphenes result from the normal activity of the visual system after stimulation of one of its parts from some stimulus other than light," including putting external pressure on the eyes. (Interestingly, due to retinal damage, blind people can't see phosphenes caused by pressure, but they can see them when their visual cortex is electrically stimulated. In hopes of turning this phenomenon into improved vision for the blind, scientists have developed a cortical visual prosthesis, implanted in the visual cortex, that generates patterns of phosphenes. The device has been approved by the FDA for clinical trial.)

As Alcmaeon rightly pointed out, there are causes for the bursts of light beyond just rubbing your eyes: Getting hit in the eye can produce this phenomenon—as can a sneeze, a surprisingly powerful event that tends to clamp our eyes shut, Wen says.

Receiving an MRI or EEG may also trigger it. MRIs, for example, produce a changing magnetic field which can stimulate the visual cortex, making a person see these flashing lights. When it comes to an EEG, depending on the brain stimulation frequency band (Hz) used, some patients experience the phenomenon when closing their eyes, which is believed to come from retinal stimulation during the process.

And the activity doesn't only happen on Earth; astronauts in space have also been known to experience them. As reported in 2006 in the journal Vision Research, "over 80 percent of astronauts serving in today's NASA or ESA (European Space Agency) programs have perceived phosphenes at least in some missions and often over several orbits." They're mainly attributed to interactions between the eye and cosmic ray particles in space, outside the Earth's protective magnetic field.

No matter the cause, the bursts of light are perfectly normal—but that doesn't mean you should engage in excessive eye rubbing. Wen says ophthalmologists advise against rubbing your eyes or applying vigorous pressure; according to Lad, too much rubbing may be damaging to the cornea and lens or "result in a loss of fatty tissue around the eyes, causing the eyes to look deep-set."

9 Not-So-Pesky Facts About Termites

iStock.com/Thithawat_s
iStock.com/Thithawat_s

Termites get a lot of hate for chewing through buildings, but the little creatures are far more interesting—and ecologically valuable—than we often give them credit for. Unless, of course, you’re Lisa Margonelli, the author of Underbug: An Obsessive Tale of Termites and Technology, a new book that explores their amazing world. Here are nine facts about the highly social—and occasionally pesky—insects that we learned from the book.

1. THERE ARE FAR MORE TERMITES THAN PEOPLE ON EARTH.

Termite queens live up to 25 years, and can lay somewhere around 30,000 eggs a day. As a result, a single mound can be home to millions of individuals at a time. While the numbers vary from study to study, scientists estimate that the biomass of all the termites in the world is at least as great as that of humans.

2. MOST TERMITES AREN’T PESTS.

Of the 2800 named termite species in the world, the majority have no interest in eating your house. Only 28 species are known to chow down on buildings and infrastructure. Most are actually very beneficial to their ecosystems, clearing dead wood, aerating the soil with their intricate tunnel systems, and enhancing plant growth. Researchers have found that contrary to being pests, networks of termite mounds can help make dry environments like savannas more resilient to climate change because of the way termite mounds store nutrients and moisture, among other benefits.

3. TERMITES ARE GOOD FOR CROPS.

Termites can help make soil more fertile. In one study, researchers in Australia found that fields that were home to ants and termites produced 36 percent more wheat, without fertilizer, compared to non-termite fields. Why? Termites help fertilize the soil naturally—their poop, which they use to plaster their tunnels, is full of nitrogen. Their intricate system of underground tunnels also helps rainfall penetrate the soil more deeply, which reduces the amount of moisture that evaporates from the dirt and makes it more likely that the water can be taken up by plants.

4. TERMITES HAVE VERY SPECIFIC ROLES IN THEIR COLONY.

Each termite colony has a queen and king termite (or several), plus workers and soldiers. This caste system, controlled by pheromones produced by the reigning queen, determines not just what different termites do in the colony but how they look. Queens and kings develop wings that, when they’re sexually mature, they use to fly away from their original nest to reproduce and start their own colony. Once they land at the site of their new colony, queens and kings snap off these wings, since they’ll spend the rest of their lives underground. Queens are also physically much larger than other castes: The largest type of termite, an African species called Macrotermes bellicosus, produces queens up to 4 inches long.

Unlike their royal counterparts, most workers and soldiers don’t have either eyes or wings. Worker termites, which are responsible for foraging, building tunnels, and feeding the other castes in the nest, are significantly smaller than queens. M. bellicosus workers, for instance, measure around 0.14 inches. Soldier termites are slightly bigger than workers, with large, sharp mandibles designed to slice up ants and other enemies that might invade the nest.

5. TERMITES ARE ONE OF THE FASTEST ANIMALS IN THE WORLD.

Apologies to cheetahs, but termites hold the record for world’s fastest animal movement. Panamanian termites can clap their mandibles shut at 157 miles per hour. (Compare that to the cheetah’s run, which tops out at about 76 miles per hour.) This quick action allows tiny termite soldiers in narrow tunnels to kill invaders with a single bite.

6. TERMITES ARE SKILLED ARCHITECTS.

In Namibia, quarter-inch-long termites of the genus Macrotermes can move 364 pounds of dirt and 3300 pounds of water each year total in the course of building their 17-foot-tall mounds. Relative to their size, that’s the equivalent of humans building the 163 floors of Dubai’s Burj Khalifa, no cranes required. And that’s not even the tallest termite mound around—some can be up to 30 feet high. More impressively, termites cooperate to build these structures without any sort of centralized plan. Engineers are now trying to replicate this decentralized swarm intelligence to build robots that could erect buildings in a similar fashion.

7. TERMITES BUILD THEIR OWN AIR CONDITIONING.

Some termites have developed an incredibly efficient method of climate control in the form of tall, above-ground mounds that sit above their nests. Organized around a central chimney, the structures essentially act as giant lungs, "breathing" air in and out as the temperature outside changes in relation to the temperature inside. Thanks to these convection cycles, termites keep underground temperatures in their nest between roughly 84°F and 90°F.

8. TERMITES ARE FARMERS.

Humans aren’t the only ones cultivating crops. Termites farm, too. They’ve been doing it for more than 25 million years, compared to humans’ 23,000 years. Some species of termite have evolved a symbiotic relationship with Termitomyces fungi, growing fungus in underground gardens for food. When they fly off to create a new colony, termite queens bring along fungus spores from their parent colony to seed the garden that will feed their new nest. Foraging termite workers go out and eat plant material that they can’t fully digest on their own, then deposit their feces on the fungus for it to feed on. They can then eat the fungus. They may also be able to eat some of the plant material after the fungus has sufficiently broken it down. The mutually beneficial relationship has led some scientists to suggest that the fungus, which is much larger in both size and energy production than the termites, could in fact be the one in control of the relationship, potentially releasing chemical pheromones that lead the termites to build the mound they live in together.

9. TERMITES ARE MICROBIAL GOLD MINES.

As scientists begin to understand the huge role that micobiomes play in both the human body and the rest of the world, termites provide a fascinating case study. About 90 percent of the organisms in termite guts aren’t found anywhere else on Earth. In their hindgut alone, they host as many as 1400 species of bacteria. These microbes are so efficient at converting the cellulose-rich wood and dead grass that termites eat into energy, scientists want to harness them to make biofuel from plants.

Want to learn more about termites? Get yourself a copy of Underbug on Amazon for $18.

This Live Stream Lets You Eavesdrop on Endangered Killer Whales' Conversations

iStock.com/Serega
iStock.com/Serega

Southern resident killer whales, which are usually found off the coasts of Washington, Oregon, and British Columbia, are an endangered species. If you're lucky, though, you might be able to hear a pod of the killer whales chattering away from the comfort of your own home. A website spotted by The Kansas City Star lets you live stream the calls of killer whales from your phone or laptop. Dubbed Orcasound, it uses hydrophones (underwater microphones) to pick up oceanic sounds from two areas off the coast of Washington.

On the website, listeners can choose between the two locations. One is the Orcasound Lab in Haro Strait, which is situated off the coast of Washington's San Juan Islands—the "summertime habitat" of this specific ecotype of whale, according to the website. The other location is Bush Point at the entrance to Puget Sound, where the whales pass through about once a month in search of salmon. However, that hydrophone is currently being repaired.

So what do orcas sound like? They're loud, and they do a whole lot of whistling, whining, and clicking. You can hear a snippet of what that sounds like in a four-minute podcast uploaded to the Orcasound site.

There’s no guarantee you’ll hear an orca, though. "Mostly you'll hear ships," the website notes, but there's also a chance you'll hear humpbacks in the fall and male harbor seals in the summer.

The live stream isn't just for educational purposes. It also serves as a citizen science project to help researchers continue their studies of southern resident killer whales, which are in danger of starvation as Chinook salmon, their main food source, die off.

The makers of Orcasound are urging listeners to email ihearsomething@orcasound.net anytime they hear killer whales or "other interesting sounds." They can also log their observations in a shared Google spreadsheet. Eventually, developers of the site hope to roll out a button that listeners can click when they hear a whale, to make the process easier for people to get involved.

[h/t The Kansas City Star]

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