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Laurinemily via Wikimedia Commons // CC BY-SA 2.5

How Our Eyes See Everything Upside Down

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Laurinemily via Wikimedia Commons // CC BY-SA 2.5

by Katie Oliver

Beliefs about the way visual perception works have undergone some fairly radical changes throughout history. In ancient Greece, for example, it was thought that beams of light emanate from our eyes and illuminate the objects we look at. This "emission theory" ["a href="https://web.archive.org/web/20111008073354/http://conference.nie.edu.sg/paper/Converted%20Pdf/ab00368.pdf" target="_blank">PDF] of vision was endorsed by most of the great thinkers of the age including Plato, Euclid, and Ptolemy. It gained so much credence that it dominated Western thought for the next thousand years. Of course, now we know better. (Or at least some of us do: There’s evidence that a worryingly large proportion of American college students think we do actually shoot beams of light from our eyes, possibly as a side effect of reading too many Superman comics.)

The model of vision as we now know it first appeared in the 16th century, when Felix Platter proposed that the eye functions as an optic and the retina as a receptor. Light from an external source enters through the cornea and is refracted by the lens, forming an image on the retina—the light-sensitive membrane located in the back of the eye. The retina detects photons of light and responds by firing neural impulses along the optic nerve to the brain.

There’s an unlikely sounding quirk to this set-up, which is that mechanically speaking, our eyes see everything upside down. That’s because the process of refraction through a convex lens causes the image to be flipped, so when the image hits your retina, it’s completely inverted. Réné Descartes proved this in the 17th century by setting a screen in place of the retina in a bull’s excised eyeball. The image that appeared on the screen was a smaller, inverted copy of the scene in front of the bull’s eye.

So why doesn’t the world look upside down to us? The answer lies in the power of the brain to adapt the sensory information it receives and make it fit with what it already knows. Essentially, your brain takes the raw, inverted data and turns it into a coherent, right-side-up image. If you’re in any doubt as to the truth of this, try gently pressing the bottom right side of your eyeball through your bottom eyelid—you should see a black spot appear at the top left side of your vision, proving the image has been flipped.

In the 1890s, psychologist George Stratton carried out a series of experiments [PDF] to test the mind’s ability to normalize sensory data. In one experiment he wore a set of reversing glasses that flipped his vision upside down for eight days. For the first four days of the experiment, his vision remained inverted, but by day five, it had spontaneously turned right side up, as his perception had adapted to the new information.

That’s not the only clever trick your brain has up its sleeve. The image that hits each of your retinas is a flat, 2D projection. Your brain has to overlay these two images to form one seamless 3D image in your mind—giving you depth perception that’s accurate enough to catch a ball, shoot baskets, or hit a distant target.

Your brain is also tasked with filling in the blanks where visual data is missing. The optic disc, or blind spot, is an area on the retina where the blood vessels and optic nerve are attached, so it has no visual receptor cells. But unless you use tricks to locate this blank hole in your vision, you’d never even notice it was there, simply because your brain is so good at joining the dots.

Another example is color perception; most of the 6 to 7 million cone photoreceptor cells in the eye that detect color are crowded within the fovea centralis at the center of the retina. At the periphery of your vision, you pretty much only see in black and white. Yet we perceive a continuous, full-color image from edge to edge because the brain is able to extrapolate from the information it already has.

This power of the mind to piece together incomplete data using assumptions based on previous experience has been labeled "unconscious inference" by scientists. As it draws on our past experiences, it’s not a skill we are born with; we have to learn it. It’s believed that for the first few days of life babies see the world upside down, as their brains just haven’t learned to flip the raw visual data yet. So don’t be alarmed if a newborn looks confused when you smile—they’re probably just trying to work out which way up your head is.

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Courtesy of Nikon
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Microscopic Videos Provide a Rare Close-Up Glimpse of the Natural World
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Courtesy of Nikon

Nature’s wonders aren’t always visible to the naked eye. To celebrate the miniature realm, Nikon’s Small World in Motion digital video competition awards prizes to the most stunning microscopic moving images, as filmed and submitted by photographers and scientists. The winners of the seventh annual competition were just announced on September 21—and you can check out the top submissions below.

FIRST PRIZE

Daniel von Wangenheim, a biologist at the Institute of Science and Technology Austria, took first place with a time-lapse video of thale cress root growth. For the uninitiated, thale cress—known to scientists as Arabidopsis thalianais a small flowering plant, considered by many to be a weed. Plant and genetics researchers like thale cress because of its fast growth cycle, abundant seed production, ability to pollinate itself, and wild genes, which haven’t been subjected to breeding and artificial selection.

Von Wangenheim’s footage condenses 17 hours of root tip growth into just 10 seconds. Magnified with a confocal microscope, the root appears neon green and pink—but von Wangenheim’s work shouldn’t be appreciated only for its aesthetics, he explains in a Nikon news release.

"Once we have a better understanding of the behavior of plant roots and its underlying mechanisms, we can help them grow deeper into the soil to reach water, or defy gravity in upper areas of the soil to adjust their root branching angle to areas with richer nutrients," said von Wangenheim, who studies how plants perceive and respond to gravity. "One step further, this could finally help to successfully grow plants under microgravity conditions in outer space—to provide food for astronauts in long-lasting missions."

SECOND PRIZE

Second place went to Tsutomu Tomita and Shun Miyazaki, both seasoned micro-photographers. They used a stereomicroscope to create a time-lapse video of a sweating fingertip, resulting in footage that’s both mesmerizing and gross.

To prompt the scene, "Tomita created tension amongst the subjects by showing them a video of daredevils climbing to the top of a skyscraper," according to Nikon. "Sweating is a common part of daily life, but being able to see it at a microscopic level is equal parts enlightening and cringe-worthy."

THIRD PRIZE

Third prize was awarded to Satoshi Nishimura, a professor from Japan’s Jichi Medical University who’s also a photography hobbyist. He filmed leukocyte accumulations and platelet aggregations in injured mouse cells. The rainbow-hued video "provides a rare look at how the body reacts to a puncture wound and begins the healing process by creating a blood clot," Nikon said.

To view the complete list of winners, visit Nikon’s website.

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Sylke Rohrlach, Wikimedia Commons // CC BY-SA 4.0
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Animals
Scientists Discover 'Octlantis,' a Bustling Octopus City
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Sylke Rohrlach, Wikimedia Commons // CC BY-SA 4.0

Octopuses are insanely talented: They’ve been observed building forts, playing games, and even walking on dry land. But one area where the cephalopods come up short is in the social department. At least that’s what marine biologists used to believe. Now a newly discovered underwater community, dubbed Octlantis, is prompting scientists to call their characterization of octopuses as loners into question.

As Quartz reports, the so-called octopus city is located in Jervis Bay off Australia’s east coast. The patch of seafloor is populated by as many as 15 gloomy octopuses, a.k.a. common Sydney octopuses (octopus tetricus). Previous observations of the creatures led scientists to think they were strictly solitary, not counting their yearly mating rituals. But in Octlantis, octopuses communicate by changing colors, evict each other from dens, and live side by side. In addition to interacting with their neighbors, the gloomy octopuses have helped build the infrastructure of the city itself. On top of the rock formation they call home, they’ve stored mounds of clam and scallop shells and shaped them into shelters.

There is one other known gloomy octopus community similar to this one, and it may help scientists understand how and why they form. The original site, called Octopolis, was discovered in the same bay in 2009. Unlike Octlantis, Octopolis was centered around a manmade object that had sunk to the seabed and provided dens for up to 16 octopuses at a time. The researchers studying it had assumed it was a freak occurrence. But this new city, built around a natural habitat, shows that gloomy octopuses in the area may be evolving to be more social.

If that's the case, it's unclear why such octo-cities are so uncommon. "Relative to the more typical solitary life, the costs and benefits of living in aggregations and investing in interactions remain to be documented," the researchers who discovered the group wrote in a paper published in Marine and Freshwater Behavior and Physiology [PDF].

It’s also possible that for the first time in history humans have the resources to see octopus villages that perhaps have always been bustling beneath the sea surface.

[h/t Quartz]

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