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Vision and Perception Project BEST
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Vision
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Biology of the Eye – Key Terms
Retina Optic Nerve Rod Cells Cone Cells Retinal ganglion Cells Retina: layer at the back of the eye that contains photoreceptors – cells sensitive to light Optic Nerve: transmits impulses from the retina to the brain Rod Cells: photoreceptor in the retina sensitive to dim light Cone Cells: photoreceptor in the retina sensitive to bright & color light Retinal Ganglion Cells: they receives visual information from photoreceptors through two intermediate neuron types, and transmit image-forming and non-image forming visual information from the retina to several regions in the thalamus, hypothalamus, and mesencephalon, or midbrain ( and google definitions)
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Blind Spot Test Point of entry of the optic nerve on the retina with no rod or cone cells Results in blind spot To find location: Close right eye and look at right cross Move head or walk forwards and backwards until you can’t see left dot Switch eyes and look at opposite figure Insensitive = no rod or cone cells
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Illusions
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Optical Illusions Perception differs from reality
Illusions reveal how visual perception works Provides insight into psychology We will look at illusions and attempt to explain
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Illusions Light Contrast
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Hermann Grid - http://michaelbach.de/ot/lum_herGrid/
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How it Works Lateral inhibition
Retinal ganglion cells farther from the focus of vision have larger receptive ranges At intersections, four white spots in receptive region cause middle spot to appear darker At “streets”, two white spots reduce effect At focus of vision, receptive range is small enough to destroy effect
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Cornsweet Illusion - http://en.wikipedia.org/wiki/Cornsweet_illusion
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How it Works Contrast effect “What you see is not what you get”
Lateral inhibition cells Include other contrast effect ones (ex. t)
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Adelson Illusion - http://web. mit
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How it Works Local contrast between checks causes visual system to think of all light checks as lighter than all dark checks Sharp boundaries between checks outweigh soft boundaries of shadow
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Illusions Shape
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http://en.wikipedia.org/wiki/Ebbinghaus_illusion Ebbinghaus Illusion.
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How it Works Comparison to nearby objects causes illusion
Similar to earlier shadow contrast illusions
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How it Works Combination of regular and misaligned parts
Brain tries to reconcile image with understanding of world
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http://en. wikipedia. org/wiki/Caf%C3%A9_wall_illusion
Cafe Wall Illusion. The lines are parallel although they appear not to be.
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http://en. wikipedia. org/wiki/Z%C3%B6llner%27s_illusion
Zollner Illusion. Again, the lines are parallel even though they appear to not be
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http://en. wikipedia. org/wiki/Illusory_contours
A white triangle appears to be present in the foreground despite the image only consisting of black lines and shapes
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How it Works Illusory contours
Brain automatically orders images based on information
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http://en. wikipedia. org/wiki/Ponzo_illusion. Which line is longer
Which line is longer? They are both equal
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How it Works Depth perception
Perception of lower line being in between tracks whereas upper line extends over tracks
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http://psychology. about
Muller-Lyer Illusion. Which shaft (not including the arrows) is the longest? The truth is that they are all the same length, but most people see the second one as the longest.
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http://psychology. about
Muller-Lyer Illusion. Which shaft (not including the arrows) is the longest? The truth is that they are all the same length, but most people see the second one as the longest.
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How it Works Multiple conflicting explanations Depth perception
Second arrow considered farther away due to angles of arrows Similar to previous Ponzo illusion
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http://www.youtube.com/watch?v=hCV2Ba5w rcs
Ames Room rcs
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Illusions Color
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Lilac Chaser - http://www. michaelbach. de/ot/col_lilacChaser/index
Lilac Chaser - The image shows a circle made out of small pink dots, where each pink dot disappears one after another. Tell students to stare at cross in center. They should see, rather than a circle of pink dots, one green dot moving in a circle.
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How it Works Negative Retinal Afterimage
Pink color is “burnt in”, so when pink spot disappears, complementary color is perceived – green! Gestalt Effect causes brain to interpret green spots as one single spot moving in circle
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http://www. moillusions. com/2012/10/black-and-white-in-colour-again
Also displays after-image effect. Have them do it once while staring at dot and once without staring at dot to realize that image is actually in black and white.
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How it Works Color contrast
Brain understands shadows automatically, altering perception of color
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http://www. scientificamerican. com/slideshow. cfm
Chromatic pincushion grid, where it appears north-south and east-west neon blue lines are present even though these are only at the crosses of the grid.
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http://www. scientificamerican. com/slideshow. cfm
Watercolor effect, interior of the contour looks yellow due to shading on immediate inside of contour
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http://www. scientificamerican. com/slideshow. cfm
Have a volunteer try to say the color of each word (not the color each word says). It’s very difficult, showing the connections between language and perception.
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How it Works Stroop Effect
Color information and language information conflict in brain Reaction time and errors increase
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Illusions Motion
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http://www. michaelbach. de/ot/mot-ske/index. html
Stereokinetic Depth Effect - 2D image appears 3D as a result of motion
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How it Works Stereokinetic Depth Effect
Motion creates illusion of 3D from 2D image
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How it Works Illusory Motion
Positioning and color contrasts cause mind to see motion Not completely understood
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Illusions Ambiguous Images
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Spinning Dancer - http://psychology. about
Spinning Dancer - or The dancer can be seen either spinning clockwise or counter-clockwise depending on the viewer. Blinking can help cause the dancer to “reverse” direction.
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Here, the gray lines shown provide cues as to depth, allowing the viewer to see both perceptions.
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How it Works Bi-stable perception
2-D figure can be seen from different perspectives, so brain attempts to reconstruct 3-D space around it
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Illusions Impossible images
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http://cs. brown. edu/~deus/courses/optical/castle%20stairs
both by MC Escher
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http://en. wikipedia. org/wiki/File:Escher%27s_Relativity
by MC Escher by Marc Gerstein
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Discussion What have you learned about vision, perception, and psychology? How might optical illusions be used in the world, besides for entertainment or understanding perception? Advertising Movies What other optical illusions have you seen? If time, draw some illusions and share For example of use in movies: in some parts of the Lord of the Rings trilogy, Gandalf is made to look taller than the Hobbits using camera angles and optical illusions.
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