OPTICAL ILLUSIONS AND BRAIN FUNCTION Click on mouse to advance There are no circles here, is your brain fooled?

Eyes send information to the cerebral cortex of the brain

Only four types of visual information are sent to the brain: Color Motion Form Depth The brain has to make sense of this information To determine things like size and direction.

And the brain can interpret information incorrectly, which is the basis of… OPTICAL ILLUSIONS You will be examining five different types of optical illusions to learn more about how the brain functions.

Impossible Triangle (and other impossible figures) At first glance this looks like an ordinary triangle, But can it really exist in three dimensions (3-D)?

What people commonly see: Each corner looks possible, but the figure as a whole appears impossible. There are many examples of “impossible” figures (they were often used by the artist M.C. Escher)

How the illusion works: The figures are drawn so the cues for depth are misleading. This includes: (1) drawing straight lines that would not work in 3-D, (2) substituting 90 o angles for other angles, and (3) shading external lines so they seem like the boundary of the shape.

What this indicates about brain function: The brain is having difficulty making a 3-D interpretation of the pictorial representation. Our brain works on a “Generic View Principle,” that you are viewing something that is consistent with past experiences. Our brains search for consistency when interpreting visual data.

Think you can’t be fooled? All of the following have straight lines with careful placement and shading. (use the ruler at you table to check if you like)

Figure/Ground Ambiguity What do you see here? Did you see the word “liar?”

What people commonly see: Most people see one figure when they first see these illusions, but once they see both figures, they can never see just one again. There are many examples of “figure-ground” illusions: Faces/VaseLift/Dark Shapes

How the illusion works: The artist usually incorporates two features: (1) sharply contrasting shades or colors, and (2) the figures share a border outline. Face/Man with SaxTwo WomenRabbit/Duck

What this indicates about brain function: The first figure you see generally indicates that you have a clearer visual memory of that shape (such as a vase or a woman’s face). Once you see the other figure, you have learned it, new neural connections have been formed in the brain. Four PeopleThree People Past experiences impact perception and learning.

Feeling a little uneasy? This is common. The brain is registering conflicting perceptions, which may trigger a release of hormones (including epinephrine) Take a few deep breaths to restore homeostasis!

Color and Contrast Perception (Substitute for Cast Shadow and Ball in manual) Besides white, how many colors are in this image? If you said two, you are right!

What people commonly see: Colors often appear different, depending on nearby colors and shades. These squares are the same shade of blue!

How the illusion works: The illusions have been drawn with particular colors that sharply contrast with one another. Both of the gray squares are the same size and color

What this indicates about brain function: Two things are happening here: (1) nearby colors stimulate additional visual receptors to send messages to the brain, and (2) the brain interprets these signals as different colors. The cerebral cortex (the brain) is “fooled” by the extra visual information. Accurate visual perception relies on both information from the eyes and the interpretation in the brain. These are actually circles, not a spiral!

Contrasting shades of black and white can also mislead the brain, resulting in “ghost” images. (This can really make you dizzy – deep breaths!)

Size Constancy Illusions These people are all the same size! Don’t believe it? Try measuring with the ruler at your table.

What people commonly see: The figures look like they are different sizes, Even if they are identically the same size.

How the illusion works: Lines and shading are used to send false perceptual cues. Optical illusions appear in many paintings PillarGallows

What this indicates about brain function: The brain determines size by extrapolating from visual cues (color, depth, motion, and form). If these cues are incorrect or misleading, the perception of size is affected. Visual perception is dependent on accurate cues.

Ames Room You look through a peephole in a wall with one eye And this is what you see… That’s not right… Adult Child

The “Ames Room” is a sophisticated illusion that builds on many of the characteristics of previous illusions, particularly size constancy. Peephole What people commonly see: Two people appear to be the same size even though they shouldn’t be.

Multiple strategies can be used on a smaller scale, such as this Necker Cube. (Stare at the cube for several seconds, and the circle will appear to move from the front face of the cube to the back) How the illusion works: The designers have incorporated a lot of features, including: altered shaped tiles and windows, angled horizon line, and contrasting colors.

Color and shape can be used to trigger 3-D perceptions. “Magic Eye” images have a 3-D image embedded within a 2-D image. (Difficult to do on a computer, try the handout at your table). Place picture a few inches from your nose. Let your eyes lose focus and the “hidden” 3-D images may spring into focus. Statues “pop” out at you (look 3-D)

What this indicates about brain function: For visual illusions that deceive the brain to see 3-D, multiple “miscues” are needed. Other senses must also be controlled. Visual perception is impacted by the other senses. This illusion accompanied by a wavering tone can cause some people to lose their balance

Summary: Our brains search for consistency when interpreting visual data. Past experiences impact visual perception And learning. Visual perception depends on information from the eyes and interpretation in the brain. Visual perception is dependent on accurate cues. Visual perception is impacted by other senses.

Sources of the Illusions: