In this exercise you will do some research behind an optical illusion of your choice and present your findings to the class. Often what we perceive in the visual world does not match with what our eyes and brains actually see. This is because our brains are continuously interpreting what the eye is telling it in the context of what it is expecting to see. This results in some often impressive distortions of the outside world known as visual, or optical, illusions. In some cases the illusion is a quirk of how the visual system works, in others it is a feature. For example, some illusions, like the fading illusion with the moving dot that you saw in the previous lesson, are a result of your visual system’s ability to adapt to stationary stimuli so it can better detect changes. Other illusions deal more with higher level visual processing in the brain, in which expectation of how the world is usually perceived interfere with how you perceive the world. Let’s go over a couple of examples. In the picture below, stare for a bout 30 seconds to a minute at the three dots in the center of the image. When time is up, shift your eyes to the mark in the middle of the blank frame on the right.
Cool, no? What you should see is a full color version of the picture on the left, at least for a few fleeting seconds. That is because your eye has adapted to the colors in the image and what you see is the resulting complementary color that briefly shows up when you see a blank image. This illusion is occurring entirely within your eye. Now let’s look at this next one. When you look at this image you will likely see a series of spirals with alternating blue, pink and green bands. Except, that the blue and green bands are actually the same color!
If you use a photo editing program to sample colors from each of the bands, this is what you end up with:
This is because perception of color does not entirely occur in your eyes, but it is perceived by your visual system within the context of surrounding colors. Notice that the finer lines inside the green bands are orange while the bands interleaved with the blue are pink. This changes the context at which we see the color and makes look like two completely different colors.
The following two videos explain a two other illusions and how the wiring of your visual system distorts what we perceive, the first is from a TedEd talk by Mark Changizi, the second one was produce by Brown University students as part of a communicating science through animation course:
1. Search through the resources below and pick one visual illusion you really like.
2. Among the resources listed you will find literally hundreds to pick from along with explanations of why they work. Your job is figure out a neuroscience-based explanation about how the illusion works and prepare a presentation for your classmates.
Be sure to, at minimum, address the following questions:
Describe your optical illusion, what do we see/not see?
Describe the neural bases of how your illusion works.
What does your optical illusion tell us about the visual system?
Include any other interesting information that you’d like to share about the illusion -- (e.g., a certain artist would make use of it, it is the basis of cinema, only works for some people, etc.)
3. Once your presentation is complete, click your section's blog in the navigation column on the left and upload all your material as blog post.
4. Comment on two other blog posts from your peers and reply to any comments on yours.
5. Lastly, return to this page, click '+Submit Assignment' and enter the url of the blog containing your work. (Remember: Post the URL of your individual blog post, not the section's blog).
Bonus Question: Before you go off to find a cool illusion, check this one out, it is one of my favorites. Can you figure out how this one works (works best in full-screen mode)?