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The science behind these optical illusions, with examples.

To celebrate CuriOdyssey’s outdoor zoo and outdoor, contact-less science exhibition Illusions opening, we are sharing some of the illusions you’ll see – we recommend using a ruler to check these illusions, they are so good at tricking your brain with the science of perception that you won’t believe your eyes. Curious? Plan your visit or learn about our camps & classes! Or, pick up some at-home science at shop.CuriOdyssey.org.

PONZO ILLUSION – What do you observe about the size of these buses? Psychologist Mario Ponzo suggested in 1911 that the human mind judges an object’s size based on cues in the background. Our brains readily perceive depth, even in flat photos and interpret the size of objects in the photo accordingly. The images of these buses, however, are the same size.
ILLUSORY MOTION – As you gaze at this image, do you perceive any movement? This optical illusion is a static image which appears to be moving due to the cognitive effects of interacting color contrasts, object shapes, and position.
ROTATING RINGS – Do you perceive any spinning movement as you look around this image? This illusion is one of many peripheral drift illusions. The perception of motion is caused by the brain’s interpretation of patterns seen outside of the eye’s area of focus. The illusion depends on a repeating pattern of high contrast, light and dark colors.
CHECKER SHADOW ILLUSION – Which square is darker gray, 1 or 2? This illusion, originally published by Professor Edward H. Adelson of MIT, illustrates how the brain can be tricked by its complex processing of visual input, perceived lighting conditions and previous experience. 1 and 2 are actually the same gray color.
TWISTED CORD ILLUSION – Do you see a spiral, or a series of rings? This optical illusion was first described by psychologist Sir James Fraser in 1908. It is sometimes called a “false spiral” because it is actually a set of concentric striped rings.
EBBINGHAUS ILLUSION – Which red dot is larger, left or right? This illusion of relative size perception was discovered by psychologist Hermann Ebbinghaus. Your brain makes a comparison of relative size based on the surrounding dots. The red dots in the center are actually the same size.
CAFÉ WALL ILLUSION – What do you notice about these rows of squares? In this geometrical optical illusion, the staggered rows of dark and light squares may appear to be sloping or curved, although the lines dividing the rows are actually parallel and straight.
SCINTILLATING GRID ILLUSION – Do you see dots at the intersecting lines? If you move your eyes around what do you notice? This optical illusion, discovered by E. and B. Lingelbach and M. Schrauf in 1994, may be the result of a neural process called “lateral inhibition”, though further research is being done to fully understand this illusion.
MÜLLER-LYER ILLUSION – What do notice about the relative lengths of the two red lines? The arrowheads and arrowtails alone may affect your perception of the line length. In this image, those lines are extended to create a dimensional drawing of walls, where the red line in the far corner appears to be full wall height, while the closer red line is not. But the red lines are actually the same length.
HERING ILLUSION – Do the red lines appear straight or bowed? This geometrical-optical illusion was discovered by physiologist Ewald Hering in 1861. The two lines presented in front of the radial background appear to bow outward, but are actually straight, parallel lines
DIVERGENT PERSPECTIVE – Is the bridge tower in the right photo leaning to the right? Our brains have learned that objects receding from view tend to visually converge towards a common point. These two towers in the side-by-side identical photos do not appear to be converging, so our brains perceive them to diverge, with the right one leaning just a bit.
PERIPHERAL DRIFT ILLUSION – What do you notice while gazing at the patterned circle in the center of this image? The apparent lighting source for the grid pattern differs between the center and peripheral areas. A sawtooth luminance grating peripheral to our field of focus is known to generate an illusion of motion as our brain resolves conflicting cues about lighting.
BEZOLD EFFECT – What colors are the two eagles? Wilhelm von Bezold discovered that a color may appear different depending on its relation to adjacent colors. These bird silhouettes are the same shade of red, but are intersected with either yellow or blue bars, which changes how we perceive the red color.
COLOR CONTEXT ILLUSION – What color are the bobcat’s eyes? The color surrounding an object can affect how the brain perceives the color of that object. Both cat eyes are exactly the same color of gray, but the red color surrounding the left eye, causes us to perceive the eye as light teal.

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