The brain has two hemispheres, each divided into four lobes. Each lobe is responsible for different functions. For instance the frontal cortex (in blue below) is responsible for decision making and planning; the temporal lobe (in green) for language and memory; and the parietal lobe (in yellow) for spatial skills. The occipital lobe (in red) is entirely devoted to vision: It is thus the place where visual illusions happen.
The frontal lobe represents around 41% of total cerebral cortex volume; the temporal lobe 22%; the parietal lobe 19%; and the occipital lobe 18%. How the visual system processes shapes, colors, sizes, etc. has been researched for decades. One way to understand more about this system is to look at how we can trick it, that is, to look at how the brain reacts to visual illusions.
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10 visual illusions to combine fun and learning about the visual system (You’ll find answers and explanations at the end of the article)
We know you know there is a trick since these are illusions… but don’t try to be smarter than your brain: Just enjoyed being tricked!
1. Are the squares inside the blue and yellow squares all the same color?
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2. Are the horizontal lines straight or crooked?
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3. Are the circles static or moving?
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4. How many legs does this elephant have?
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5. Can you put the fish in the fishbowl?
Stare at the yellow stripe in the middle of the fish in the picture below for about 10-20 sec. Then move your gaze to the fish bowl.
ANSWERS AND EXPLANATIONS: Contrast your answers with the ones below, and learn about what was going on in your brain while you experienced each of these illusions:
1. Can you put the fish in the fishbowl?
Did you see a fish of a different color in the bowl? You have just experienced an afterimage. In the retina of your eyes, there are three types of color receptors (cones) that are most sensitive to either red, blue or green. When you stare at a particular color for too long, these receptors get “fatigued.” When you then look at a different background, the receptors that are tired do not work as well. Therefore, the information from all of the different color receptors is not in balance. This will create the color “afterimages.”
2. Bezold effect
The smaller squares inside the blue and yellow squares are all the same color. They seemdifferent (magenta and orange) because a color is perceived differently depending on its relation to adjacent colors (here blue or yellow depending on the outer square)..
3. Café Wall Illusion
The horizontal lines are straight, even though they do not seem straight. In this illusion, the vertical zigzag patterns disrupt our horizontal perception.
4. Illusory Motion
The circles do appear to be moving even though they are static. This is due to the cognitive effects of interacting color contrasts and shape position.
5. How many legs does this elephant have?
Tricky, isn’t it?! This picture is an impossible picture that also contains some subjective contours, such as the Kanizsa Triangle below: A white triangle (pointing down) can be seen in this figure even though no triangle is actually drawn. This effect is known as a subjective or illusory contour. The contour of the triangle is created by the shapes around it.
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