The Neuroscience of Yoricks’s Ghost and Other Afterimages
Yoricks's Ghost
Alas! Poor Yorick. I knew him well. A fellow of infinite jest, of most excellent fancy; he hath borne me on his back a thousand times; and now, how abhorred in my afterimage he is!
Well… that’s what Hamlet would have said, had he been holding the vintage Pear’s Soap advertisement bearing Yorick’s skull in the accompanying slide, rather than a dug up and rotting Danish cranium. In this antique illusion, you can stare at the X in Yorick’s left eye socket for about 10 to 30 seconds, then look away at a flat surface such as a piece of paper, wall, ceiling or sky, and you will see Yorick’s afterimage as a ghostly apparition. Read More.
Optical Illusions and the Illusion of Love
Akiyoshi Kitaoka
It’s Valentine’s season, which means that everywhere you look there are heart-shaped balloons, pink greeting cards and candy boxes filled with chocolate. But what is true love? Does it exist? Or is it simply a cognitive illusion, a trick of the mind? Let us count the ways. Contrary to the anatomy referenced in all of our favorite love songs, love (as with every other emotion we feel) is not rooted in the heart, but in the brain….
Sculpting the Impossible: Solid Renditions of Visual Illusions
Sculpting the Impossible
In an impossible figure, seemingly real objects—or parts of objects—form geometrical relations that physically cannot happen. The artist M.C. Escher, for instance, depicted reversible staircases and perpetually flowing streams, whereas mathematical physicist Roger Penrose drew his famously impossible triangle and visual scientist Dejan TodoroviTodorovi created an Elusive Arch that won him Third Prize of the 2005 Best Visual Illusion of the Year Contest. These effects challenge our hard-earned perception that the world around us follows certain, inviolable rules. They also reveal that our brains construct the feeling of a global percept, “or individual item we perceive,” by sewing together multiple local percepts. As long as the local relation between surfaces and objects follow the rules of nature, our brains don’t seem to mind that the global percept is impossible. Read more …
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Art as Visual Research: 12 Examples of Kinetic Illusions in Op Art
Courtesy of Akiyoshi Kitaoka
Scientists did not invent the vast majority of visual illusions. Rather, they are the work of visual artists, who have used their insights into the workings of the visual system to create visual illusions in their pieces of art. We have previously pointed out in our essays that, long before visual science existed as a formal discipline, artists had devised techniques to “trick” the brain into thinking that a flat canvas was three-dimensional, or that a series of brushstrokes in a still life was in fact a bowl of luscious fruit. Thus the visual arts have sometimes preceded the visual sciences in the discovery of fundamental vision principles, through the application of methodical—although perhaps more intuitive—research techniques. In this sense, art, illusions and visual science have always been implicitly linked. Read more …
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Illusions: Motion from Brightness
Lucy in the sky
Benjamin Franklin once said, “Never confuse motion with action.” But if motion is not action, then what exactly is motion? Let’s break it down.
Imagine you are pointing your video camera at your favorite ball game. Inside your camera is a lens that focuses the image onto a CCD chip, which is a matrix of light detectors. How can a matrix of light detectors possibly see a ball rolling? The answer is, it can’t. The camera doesn’t see motion whatsoever, because the only thing light detectors can detect is changes in light magnitude, not light position. If the edge of the ball passes over a single light detector, the detector will react, but that’s trivially due to fact that the light level on the detector changed as the ball changed position. The same detector would react identically to a stationary edge that increased its brightness without having moved. To track the change in position of an object, you need to add something, such as a brain, that can interpret the output of all the detectors in concert. Read more…
Illusions: The Eyes Have It
FOLLOW MY FINGER
magine you are pointing your video camera at your favorite ball game. Inside your camera is a lens that focuses the image onto a CCD chip, which is a matrix of light detectors. How can a matrix of light detectors possibly see a ball rolling? The answer is, it can’t. The camera doesn’t see motion whatsoever, because the only thing light detectors can detect is changes in light magnitude, not light position. If the edge of the ball passes over a single light detector, the detector will react, but that’s trivially due to fact that the light level on the detector changed as the ball changed position. The same detector would react identically to a stationary edge that increased its brightness without having moved. To track the change in position of an object, you need to add something, such as a brain, that can interpret the output of all the detectors in concert…. Read more …
A Perspective on 3-D Visual Illusions
The Leaning Tower of Pisa
How could we have missed it? Hundreds, perhaps thousands, of visual scientists, psychologists, neuroscientists, visual artists, architects, engineers and biologists all missed it—until now. The “it” in question is the Leaning Tower Illusion, discovered by Frederick Kingdom, Ali Yoonessi, and Elena Gheorghiu of McGill University. In this illusion, two identical side-by-side images of the same tilted and receding object appear to be leaning at two different angles (see slideshow). This incredible effect was first noticed just last year in images of the famed Leaning Tower of Pisa, but it also works with paired images of other tilted objects. Read more…
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The Neuroscience of Illusion
The Neuroscience of Illusion
It’s a fact of neuroscience that everything we experience is actually a figment of our imagination. Although our sensations feel accurate and truthful, they do not necessarily reproduce the physical reality of the outside world. Of course, many experiences in daily life reflect the physical stimuli that enter the brain. But the same neural machinery that interprets actual sensory inputs is also responsible for our dreams, delusions and failings of memory. In other words, the real and the imagined share a physical source in the brain. So take a lesson from Socrates: “All I know is that I know nothing.” Read more…
Filling in the Afterimage after the Image
2008 First prize
© 2008 van Lier & Vergeer
To do:
Fixate your gaze on the center of one of the figures and stare at it for some time (20-30 seconds) while it cycles (without moving your eyes). After several iterations you’ll start noticing that the empty outlines fill in with ghostly redish or bluish colors! These illusory colors are called “afterimages”. Interestingly, the colors of the afterimages vary, which is puzzling because they come from the same original figure. Moreover, the shape of the outlines determines the filled-in color, which is complementary to the color of the same shape in the original figure.
What’s happening?
It is well known that viewing a colored surface can induce a vivid afterimage of the complementary color (for example, the color red induces a greenish/bluish afterimage). Our illusion shows that a colored image can produce different colored afterimages at the same retinal location. The perceived afterimage colors depend on the contours that are presented after the colored image. More specifically, the illusion shows that the afterimage colors spread and mix between those contours. In addition, alternating different contours after the original colored image causes rapidly switching afterimage colors.
Read more about the illusion and possible explanations.
Van Lier, Vergeer, Anstis, 2009, Filling-in afterimage colors between the lines, Current Biology, 19 (8), R323-R324.
