Galileo’s illusion solved by New York vision researchers

Portrait of Galileo Galilei, 1605-1607, by Domenico Tintoretto. Image courtesy of Wikimedia Foundation.

Portrait of Galileo Galilei, 1605-1607, by Domenico Tintoretto. Image courtesy of Wikimedia Foundation.

It was 1632, and the father of modern astronomy was perplexed as to why Venus, when observed by “naked” eye, would appear substantially larger than Jupiter, which was actually four times larger than Venus. He knew that Venus’ exaggerated size must have something to do with it’s halo, or “radiant crown” as he described it, and that this halo must have something to do with his eyes, and not the celestial objects themselves. Observations via telescope presented a more accurate visual representation of the mathematically-verifiable proportions of the planets.

Almost 400 years later, Neuroscientists Susana Martinez-Conde and Stephen L. Macknik, eloquently explain the January 2014 published findings of the State University of New York’s vision researchers Jens Kremkow, Jose Manuel Alonso and Qasim Zaidi:

By examining the responses of neurons in the visual system of the brain—to both light stimuli and dark stimuli—the neuroscientists discovered that, whereas dark stimuli result in a faithful neural response that accurately represents their size, light stimuli on the contrary result in non-linear and exaggerated responses that make the stimulus look larger. So white spots on a black background look bigger than same-sized black spots on white background, and Galileo’s glowing moons are not really as big as they might appear to the unaided eye.

These now-isolated differences in how our photoreceptors operate also explain why it is easier to read black text on a white page, than to read white text on a black page, a topic of interest to our typographer and font designer friends.

Do you love Galileo as much as we do? Check out the GLIMPSE Cosmos issue, available in our archives.

GLIMPSE journal is an interdisciplinary supercollider of works that examine the functions, processes, and effects of vision and its implications for being, knowing, and constructing our world(s). Each theme-focused issue features articles, visual essays, interviews, and reviews spanning the physical sciences, social sciences, arts and humanities. GLIMPSE contributors are leading and emerging scholars, researchers, scientists and artists from around the world. Some of our contributors are independent thinkers and doers with no formal institutional affiliations, and others are affiliated with the most respected research institutions in the world. Read all about them.


by Myya McGregory

The Zoopraxiscope- a couple waltzing from the Library of Congress archives

Eadweard Muybridge developed the zoopraxiscope in 1876. The zoopraxiscope was a very complicated device that featured a large lense, a lamp, and a motor to show successive images printed on 16″ glass in simulated motion. This invention garnered much praise for Muybridge and he is credited as the father of the motion picture.

The National Museum of American History is exploring an interesting aspect of Muybridge’s work. They question whether his photogrpahic invention was science or art. Muybridge was able to capture incremental elements of motion and expose them in ways never seen before. While at the University of Pennsylvania in the late 1880s, Muybridge began the project of documenting human and animal locomotion. Using up to 36 different lenses and two dozen cameras each placed at 30, 60, and 90 degrees to the subject, Muybridge produced 36 negatives. The negatives were enlarged and then inked on glass plates. The succession of images, when showed on the zoopraxiscope revealed an almost scientific precision. Find out more in the Cinema Issue.

Persistence of Vision

As  many of you will soon find out in the upcoming Cinema issue, persistence of vision is «the phenomenon of the eye by which an afterimage is thought to persist for approximately one twenty-fifth of a second on the retina». While the image is burned on the retina of the eye, we have time to send signals to the brain to identify the image.

Still from a flipbook created at the Museum of the Moving Image. Credit: Julia Rubinic

Persistence of vision, though thought to be a myth, could explain why our eyes perceive one continuous, moving image when we look at a progressions of stills.

This theory not only explains flipbooks but is also the basis of many film devices of the 19th century. The idea that images remain on the retina seconds after viewing means that images can be perceived as moving at speeds as low as 5 frames per second.

This  also means that if an image vibrates fast enough, it can be perceived as static rather than kinetic.

Check out this website by the American Museum of the Moving Image to discover more.

Falling Up

Image courtesy of member Andreia Bohner

Dutch artist M.C. Escher created the Waterfall lithograph (pictured above) in 1961. Escher is responsible for some of the most well-known and beautifully mind-boggling optical illusions out there. By combining precise artistic skill with a deep understanding of mathematics, his designs explore impossibility and infinity. Escher’s work challenges our perception and forces us to look at the world in more abstract terms.

We at GLIMPSE love a good DIY project. It’s always a nice feeling to look at that bookshelf or bracelet you spent the afternoon toiling over and think to yourself, “Hey, I made that and it’s not half bad!” We also happen to love optical illusions. So imagine our delight when GLIMPSE Helvetica film discussion panelist Dyana Weissman shared with us the (now infamous) video of a do-it-yourself Escher’s Waterfall.

While we would love to believe this man somehow reversed the laws of gravity in his garage, we have a feeling some good editing and computer-generated water may have helped him out. But we could be wrong! Either way he built a pretty amazing structure that has baffled about three million people. His triumphant thumbs-up at the end of the video seems more than appropriate.

Allison Nonko

Renaissance Visions in “The Legend of the True Cross”

Image courtesy of Jakob Montrasio, MK Media Productions.

Piero della Francesca, like many other artists of the Renaissance, sometimes used linear perspective despite the fact that it would be impossible to view his work from the correct station point when on display … For him, perspective was not merely a technical  convention for representing a physically correct world. It was just one of many devices that could be adapted for use for other, non-optical ends. Our hypothesis is that the perspective in Piero’s fresco cycle depicting The Legend of the True Cross in the cappella maggiore of San Francesco in Arezzo is less about coherent space than about drawing attention to important narrative details … by which the artist hoped to instill in the viewer a sense of spiritual rapture.

Excerpt from Drs. Robert Belton and Bernd Kersten’s “Vision and Visions in Pierro della Francesca’s Legend of the True Cross.”  Issue 6, Visions. Read the full article in GLIMPSE’S Visions issue at

And the award goes to….

Amid much oohing and aahing at the Philharmonic Center for the Arts in Naples, Fla. last Monday, mathemetician Kokichi Sugihara defied gravity. During the latest Vision Sciences Society meeting,  he stood in front of a large screen that displayed the impossibe: four wooden balls rolling uphill, climbing a series of ramps and meeting at the top in the center. The contraption won him the award for Best Visual Illusion of 2010.

The balls appear to be pulled up the slopes by a magnet, but in fact, understanding the angle of the ramps themselves is the key to deciphering the illusion. The gravity-defying stunt that we’re witnessing can only appear to take place from one and only one vantage point. Which is, of course, our vantage point when viewing the video. Take just one step to your left (or right or up or down), and you’ll see the ramps for what they are: downward-sloping and of varying lengths.

The magic, as it is with most things, lies in the way we see.

For more riddles, stunts and bits of perceptual magic, check out the honorable runners-up from this year’s award ceremony.

The truth, with shades of gray

If you’ve ever claimed to know the facts because you’ve “seen it with your own eyes,” you probably haven’t come to grips with the ugly truth: Our vision lies to us.

Professor Edward H. Adelson of MIT offers a case in point. The image shown in Adelson’s Checker-Shadow Illusion, to your eye and mine, doesn’t seem to present anything terribly illusory–a green cylindrical object casting a shadow across a gray and white checkerboard. Done.

Or it would seem…

When the brain interprets the visual information in this setup–specifically, the color information–it does so while considering context. We know the square marked A is definitely gray, and the square marked B is clearly white. And we know this because A and B are defined by their surrounding local colors–white and gray, respectively. But you’ve already been made the fool, yet again, by your visual system! Take a pair of scissors to the checkerboard, cut out B, place it on A.  They’re the same.

Really, they are.  See for yourself. Don’t trust what you see? Here’s the proof.

But before you get too paranoid that your brain and eyes are in cahoots against you, we leave you with this bit of reassurance, courtesy of Dr. Adelson:

As with many so-called illusions, this effect really demonstrates the success rather than the failure of the visual system. The visual system is not very good at being a physical light meter, but that is not its purpose. The important task is to break the image information down into meaningful components, and thereby perceive the nature of the objects in view.

Stay tuned for Glimpse‘s Visions issue, where we’ll take you beyond tricks of the eye into the realm of the visually inexplicable…