Physics 1230: Light and ColorIvan I. Smalyukh, Instructor

Office: Gamow Tower, F-521Email:

ivan.smalyukh@colorado.edu

Phone: 303-492-7277

Lectures: Tuesdays & Thursdays,

3:30 PM - 4:45 PMOffice hours:

Mondays & Fridays, 3:30 PM – 4:30 PM

TA: Jhih-An Yang jhihan.yang@colorado.edu 

Class # 19

Midterm Exam #2

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• HW5, Due Tuesday, Nov 8

• Chapter 7 – finish today

•Exam Overview Today/Thursday (Nov 3)

•Exam: Nov. 10, Thursday

•Science lab tour – to be announced;

Interesting collective behavior 3: Sensitive to a MOVING World. Time and motion important.

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Fatigue: prolonged stimulation (staring at a lamp) causes a weaker response and a negative afterimage.

Successive lightness contrast: a gray object looks darker after looking at white.

Positive afterimage: We see a flash as a bright spot after it has gone away. Over stimulated nerves keep firing.

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Fatigue and Involuntary eye movement

Eye movement moves the image around so that new areas are stimulated.

Without eye movement, images fade. This has been verified by experiments that fix the image on the retina.

Eye movement causes wavy lines to appear as though in motion, because the afterimage interferes with the moved image.

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The eye is moving all the time. It corrects for motion…

8http://www.michaelbach.de/ot/mot_eyeJitter/index.html

The only difference between the center and edge is the lack of any feature to “focus” on.

IF there are edges, but not if edges are absent.

Other illusions

There are many optical illusions with varying explanations. Many are poorly understood.

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Are the blue shades the same?

Lateral inhibition cannot explain this!

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Lateral inhibition alone does not explain this effect, the Munker-White illusion.

Müller-Lyer illusion

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http://www.newworldencyclopedia.org/entry/Muller-Lyer_illusion

Which arrow is longer?

Müller-Lyer illusion

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http://www.michaelbach.de/ot/index.html

This is the back corner of a room, it is further away, hence it must be larger.

Big Moon Illusion

15What you remember. Actual

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Frankfurter illusion

http://www.michaelbach.de/ot/sze_Frankfurter/index.html

While focused on the background, hold your two index fingers horizontally in front of your eyes, not touching. A piece of finger will appear to float in space.

Are the lines straight?

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Hering Illusion

Does the square have straight sides?

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Does the square have straight sides?

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http://www.michaelbach.de/ot/ang_hering/index.html

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Poggendorff Illusion

21http://www.michaelbach.de/ot/ang_poggendorff/index.html

Are the lines continuous and straight “behind” the yellow columns?

Poggendorff Illusion

22http://www.michaelbach.de/ot/ang_poggendorff/index.html

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Art that mimics 3-d.

Motion after effect

Motion channel, keeps firing after watching a moving object, causing motion aftereffect.

http://www.michaelbach.de/ot/mot_adaptSpiral/index.html

The following are from Akiyoshi KitaokaDepartment of Psychology, Ritsumeikan University, Kyoto, Japan:http://www.psy.ritsumei.ac.jp/~akitaoka/saishin27e.html

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Motion illusion (A. Kitaoka)Note that each green circle is rotated slightly from its neighbor.

As your eye jumps around, it sees the circles rotation.

Are the ropes tangled?

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from Akiyoshi Kitaoka

Motion illusion (Kitaoka)

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Motion illusion (Kitaoka)

29Snakes - Akiyoshi Kitaoka

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Dead Snakes - Akiyoshi Kitaoka

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Motion effects from Michael Bach’s web page

• Silhouette illusion• Motion induced blindness• Motion aftereffect (Waterfall illusion)• Spiral aftereffect (motion channel activated)• Breathing square

http://www.michaelbach.de/ot/index.html