OPTICAL ILLUSIONS AND BRAIN FUNCTION

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Thereare nocircleshere,

is yourbrain

fooled?

Eyes send information to thecerebral cortex of the brain

Only four types of visual informationare sent to the brain:

Color

Motion

FormDepth

The brain has to make sense of this informationTo determine things like size and direction.

And the brain can interpret informationincorrectly, which is the basis of…

OPTICAL ILLUSIONS

You will be examining five different typesof 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 awhole 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 depthare misleading. This includes: (1) drawingstraight lines that would not work in 3-D,(2) substituting 90o angles for other angles, and(3) shading external lines so they seem likethe boundary of the shape.

What this indicates about brain function:The brain is having difficulty making a 3-Dinterpretation of the pictorial representation.Our brain works on a “Generic View Principle,”that you are viewing something that isconsistent with past experiences.

Our brains searchfor consistency

when interpretingvisual data.

Think you can’t be fooled?All of the following have straight lineswith 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 firstsee these illusions, but once they see bothfigures, they can never see just one again.

There are many examples of “figure-ground” illusions:

Faces/Vase Lift/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 Sax Two Women Rabbit/Duck

What this indicates about brain function:The first figure you see generally indicatesthat you have a clearer visual memory of thatshape (such as a vase or a woman’s face).Once you see the other figure, you havelearned it, new neural connections havebeen formed in the brain.

Four People Three People

Past experiencesimpact perception

and learning.

Feeling a little uneasy?

This is common. The brain is registeringconflicting perceptions, which may trigger

a release of hormones (including epinephrine)

Take a few deep breaths torestore 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 onnearby colors and shades.

These squares are the same shade of blue!

How the illusion works:The illusions have been drawn with particularcolors 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) nearbycolors stimulate additional visual receptors tosend messages to the brain, and (2) the braininterprets these signals as different colors.The cerebral cortex (the brain) is “fooled”by the extra visual information.

Accurate visualperception relies

on both informationfrom the eyes andthe interpretation

in the brain.

Theseare

actuallycircles,not a

spiral!

Contrasting shades of black and white can alsomislead 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 falseperceptual cues.

Opticalillusionsappearin many

paintings

Pillar Gallows

What this indicates about brain function:The brain determines size by extrapolatingfrom visual cues (color, depth, motion, andform). If these cues are incorrect ormisleading, the perception of size is affected.

Visual perception isdependent on accurate cues.

Ames RoomYou 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 illusionthat 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 eventhough they shouldn’t be.

Multiple strategies can be used on asmaller scale, such as this Necker Cube.

(Stare at the cube for several seconds, and the circle willappear to move from the front face of the cube to the back)

How the illusion works:The designers have incorporated a lot offeatures, including: altered shaped tiles andwindows, angled horizon line, and contrastingcolors.

Color and shape can be used to trigger3-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 tosee 3-D, multiple “miscues” are needed. Othersenses must also be controlled.

Visual perceptionis impactedby the other

senses.

This illusion accompaniedby a wavering tone can

cause some people to losetheir balance

Summary:

Our brains search for consistency wheninterpreting visual data.

Past experiences impact visual perceptionAnd learning.

Visual perception depends on information fromthe eyes and interpretation in the brain.

Visual perception is dependent on accurate cues.

Visual perception is impacted by other senses.

Sources of the Illusions:

http://www.geocities.com/SoHo/Museum/3828/home.html

http://www.eaglehawksc.vic.edu.au/kla/art_graphics/illusion/index.htm

http://www.manworthy.freeserve.co.uk/optill/oind.htm

http://www.magiceye.com/index.htm