1. Journal 2/10/17 Objective Tonight’s Homework
In the picture shown are two points: A and B. Which is darker? What do you think is going on here and why do you think it works?
Objective Tonight’s Homework
To see some of the ways our eyes can be tricked
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2. Optical Illusions
Cause: Your brain is conditioned to notice objects and categorize them based on their surroundings.

3. Optical Illusions
This is related to the last one. The two grey vertical bars are the same color, but don’t appear the same due to surroundings

4. Optical Illusions
This is related to the last one. The two grey vertical bars are the same color, but don’t appear the same due to surroundings

5. Optical Illusions
What do you see at the points where the grey lines intersect? What’s happening with the dots?
This is one of many “afterimage” and contrast illusions we’ll see.

6. Optical Illusions
Stare at the image for about 30 seconds. Then quickly close your eyes.
What do you see?
This is also an “afterimage” illusion, created by the brain trying to “see” something after it vanishes.

7. Optical Illusions This is known as the café wall illusion.
The grey lines look crooked but they’re actually parallel.

8. Optical Illusions This is known as the café wall illusion.
The grey lines look crooked but they’re actually parallel.

9. Optical Illusions This is also a context illusion.
The grey bar in the middle is just one shade of gray. Your brain is using context to confuse you.

10. Optical Illusions This is also a context illusion.
The grey bar in the middle is just one shade of gray. Your brain is using context to confuse you.

11. Optical Illusions Other context illusions are shown here as well.
The orange dots are the same size, the yellow lines are the same.

12. Optical Illusions Other context illusions are shown here as well.
The red lines are parallel and the two line segments are the exact same size.

13. Optical Illusions Other contexts can produce very different results.
Below are two squares, each with a circle in the middle. Which circle has the sharper, less “fuzzy” pattern of black and white?

14. Optical Illusions
The brain is also susceptible to a number of motion illusions as well. The brain tries to put together images to create motion.
You know that this is how things like movies and TV work.
But the eye itself can only process images so fast. This is at a rate of somewhere around 70 per second. If something is changing faster than that, the eye can’t capture every moment, so it starts to skip. This is why when something moves fast enough, it appears to move the opposite way instead.

15. Optical Illusions
We see a similar effect in the “barberpole” illusion. In reality, the black and white bars are moving down-right at a 45 degree angle.
But our eyes are being restricted to a narrow field of vision. This makes our eyes think that things are moving in the direction we’re being conditioned to see. In this case, vertical.

16. Optical Illusions
Similarly, this one plays on your brain thinking the vertical is important. And skewing what you’re seeing in an up-down way.
Which line does the black one connect to?

17. Optical Illusions
Similarly, this one plays on your brain thinking the vertical is important. And skewing what you’re seeing in an up-down way.
Which line does the black one connect to?

18. Optical Illusions
Other illusions are based on apparent motion. Does it look like the image below is moving?

19. Optical Illusions
Or this?

20. Optical Illusions
Or this?

21. Optical Illusions
Or try this one. Stare at the dot in the center and move your head back and forth.

22. Optical Illusions
Some illusions are based on your eye expecting to see something, like the obvious other triangle in this image.

23. Optical Illusions
Some are based on the brain’s desire to see things in 3-D if both eyes get a slightly different image. This is an autostereogram, or “Magic eye”

24. Optical Illusions
And lastly are ones where your brain is trying to see 3-D, but doesn’t have enough information to put all the pieces together. Which way is the dancer spinning? Clockwise or counter-clockwise?