WTSM 100L: Patterns in Nature

Study guide for third exam (Tuesday, December 4, 2007)

Ground rules

You may bring a 3” x 5” index card on which you may write anything you want. You must turn this card in with your completed exam. You may bring a calculator (and may program it as you wish, but be sure you know how to use it and be sure the batteries are charged). No other assistance will be permitted.

Full credit will not be given on any mathematical question unless you show your work (for example, make it clear what formula/procedure you’re using and what numbers you’re plugging in) and indicate your answer clearly. On questions requiring verbal answers, your answers should be clear, specific, correct, and complete. You may supplement your words with clearly labeled sketches or illustrations.

The format will be similar to the previous two exams. This exam will cover the topics below.

Visual illusions

• Give some reasons why the scientific study of visual illusions is important.
• Explain what “cognitive impenetrability” is in the context of visual illusions.
• Describe the T (or Gateway Arch) illusion. Describe some tests one might do to see what causes this illusion.
• Describe (don’t just name) an illusion that we looked at that falls into the category of 3D interpretation.
• What feature of the mammalian eye causes the blind spot phenomenon? Why are we generally unaware of the existence of the blind spot? Do all creatures with eyes have a blind spot?
• Describe the phenomenon of retinal bleaching. Use the fact the white light is made up of all colors, the fact that most people have red-sensitive, blue-sensitive, and green-sensitive cones on our retina, and the phenomenon of retinal bleaching to explain why colored afterimages are seen after staring at a colored pattern for a long time. Also be able to explain what color afterimage would be seen in a particular case. (This would involve being able to match the three primary colors with their complements.)
• Describe (don’t just name) example(s) of visual illusions that were recognized by ancient peoples such as the Greeks.
• Describe a visual illusion that affects how the Parthenon is perceived, and show how the Greek architects compensated for this illusion (two possible answers).
• In the "Seeing is Deceiving" reading, pp. 3-4, we saw that Greek thinkers generally held one of two viewpoints about visual illusions and perception. Describe these two points of view. Discuss one of the following illusions (I'd give you pictures or graphics on the exam) and describe how these two points of view are supported or challenged by the illusion:

Filling in a pattern so that it appears uninterrupted even through the region of the blind spot

Triangle illusion (http://www.colorcube.com/illusions/triangles.htm)

Pyramid illusion (http://www.michaelbach.de/ot/lum_pyramid/index.html)

Self-organization and cellular automata

• Explain what a cellular automaton is, and what four features need to be specified to define a particular cellular automaton.
• For a given 1D cellular automaton and a given starting condition, find the next several generations.
• For a given starting condition in the Game of Life (2D CA grid with a neighborhood of 9 and rules: 2 or 3 neighbors: survive; 3 neighbors: born), find the next generation.
• Explain what self-organization is and what features characterize it. Based on this, explain why cellular automata are good models of self-organization.
• Give some examples of self-organized patterns in nature that have adaptive advantages (and explain why they do). Give some examples of self-organized patterns in nature that are just epiphenomena (and know what “epiphenomena” means in this context). Give some examples of patterns in nature that are not self-organized.
• Is flocking (of birds, fish, insects, etc.) an example of self-organized behavior or not? Explain why or why not.
• Describe the reaction-diffusion process by which it’s believed many animal coat patterns are formed.
• Explain what positive and negative feedback are, and why both are necessary to make animal coat patterns.
• Give two “economical” reasons (from the Patterns in Nature reading) why self-organization is a useful concept with which to understand many patterns in nature.