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Magical optical illusions divided society into two groups during the 1990s – those who could see hidden images and those who could not. These dot images, known as autostereograms, create a three-dimensional image when the viewer looks at a two-dimensional pattern in a certain way.
Magic lasting 25 years
And although the mysteries of optical illusion were confusing until about 25 years ago, this idea has long been used by researchers to study the perception of vision. Pictures are viewed at a “diverging” distance equal to the width of one repetition of the two-dimensional “visible” pattern. This forces you to see several distorted hidden objects in 3D at once. Divergent viewing means that instead of looking directly at the image, you move your eyes as if you are looking straight through it. Stereograms were first used in the study of the perception of human vision, in particular, the visibility of different images. In this case, the brain creates a single cohesive picture – the autostereogram does not require a special machine to view the hidden three-dimensional image.
The pictures are usually spaced 66 millimeters apart, which means that each eye that sees the pictures perceives them differently. The brain during this process tries to create a complete image so as not to experience double vision. This is also because the eyes help the brain make the best possible approximation, which is known as stereopsis, a term associated with the perception of depth and three-dimensional structures.
Illusion – a method of studying vision
This idea dates back to the 1930s and was first described by English inventor Charles Wheatstone. He created a device that displays a different image for each eye in order to understand how the organ takes on the image of three-dimensional objects. Using flat images, for the first time, researchers have been able to trick the brain into depth perception by creating a stereopsis. The next major breakthrough came in 1959, when physician Bela Jules was able to eliminate deep cues. The scientist discovered the first stereogram of random dots while experimenting with stereopsis and created a single image in the form of randomly distributed dots.
In the first image, she selected a circular area of dots and slightly shifted the same area in the second image. The random dots contained a hidden shape that could only be seen when looking at the picture at a certain moment. Anyone looking at the two images will see a floating circle, although there were no depth cues at random points. These findings support Dr. Julesh’s hypothesis that perception occurs in the brain and not in the eyes. When you let them diverge, instead of looking straight ahead, each organ sees its own picture.
Why do we see rotating pictures?
Since the brain is trained to convert two similar images into one, it automatically assumes that you are seeing one image that deepens in vision, instead of two images that are just close to each other. This happens throughout the image, and each image is interpreted as one. Pairs of pictures that repeat at closer intervals come closer to you. So this is the repeat interval that can be manipulated to adjust the depth.
About 20 years after Julesh’s discovery, Christopher Tyler, her student, used computer programming so that this displacement scheme could be applied to a single image. This created the first black and white single image (stereogram of random dots). In 1991, Tom Bakchei, an engineer, and Cherie Smith teamed up to improve researcher Julesh and Tyler.
There are no more dots. Using this program in combination with the latest 3D modeling software and inking technique, a brand new patented art form has been developed – Magic Eye.
To create a Magic Eye image, programmers will first start with a grayscale latent image, creating a smooth gradient depth map where dark points that should be further away are darker and closer points are lighter. The 2D template is then placed on top of the hidden camouflage images. Next, the computer will use the Magic Eye algorithm, which displays the model and arranges repeating patterns to the required latent image depth. When someone looks at such an image, the repeated pattern conveys the depth information encoded in it to the brain, and the brain perceives the hidden image as an illusion.
Cave drawings imitate modern illusion
An optical illusion is when an object is perceived differently than objective reality. One of the most famous optical illusions is the “Duck Rabbit” drawing, which first appeared in Harper’s Weekly in 1892. But according to National Geographic, the researchers found that ancient man was also able to create optical illusions. In a recent work presented to an international rock art researcher convention, Duncan Caldwell showed that optical illusion plays a “recurring role” in Paleolithic art in several caves in France.
Caldwell and others have determined that the drawings of bison and mammoths in Font-de-Gaume Cave, France often exchange lines and features. As National Geographic explains, “For example, in the contemporary drawing below, the image from Font-de-Gaume has one basic body shape, an underbelly, and many legs decorated with features of both mammoths and aurochs, and have heads at both ends, creating the illusion.”
Cave art is not the only place where ancient artists copied optical illusions. A small figurine from another French area shows a bison on one side and a mammoth on the other. As noted by National Geographic, the Paleolithic artist used similar outlines of aurochs and mammoths to create an object that represents both animals. The bison and mammoth seem to be the only animals that have used optical illusions, most likely due to their similar stature.
There are three main types of optical illusions: literal – create images that are different from the creating object, cognitive – the eyes and brain make different assumptions about the object, physiological – this is what happens when light, color, tilt and movement affect the eyes and brain . Optical illusions occur in the brain due to neural retardation. Mark Changizi is a researcher at Rensselaer Polytechnic Institute in New York. He said: “When light hits your retina, about one-tenth of a second passes before the brain translates the signal into the visual perception of the world.” This foresight has evolved to help us respond to the world around us and understand what might happen to the image in the future. As Changizi explains, optical illusions happen when our brain tries to make sense of a future that doesn’t match reality.
Experts note that when children look at a picture of a “duck rabbit”, they see a duck. But if they are checked on Easter Sunday, then they think the figure of a rabbit. Step back in history and the duck becomes a bison while the rabbit turns into a mammoth.