Post on 03-Jan-2017
transcript
Magic
A Look at the Science of Illusion Magic, Percep9on, and A;en9on
James R. Pomerantz GSCS 258L, Rice University, February 2010
Why listen to a psychologist about magic?
• Much of magic involves human percep9on and a;en9on
• Understanding magic is as much about the understanding the audience member as about the magician and his mirrors, hidden wires, and cards up his sleeves.
My background
• Psychology and Cogni9ve Neuroscience: the study of eye, brain, and human percep9on
• Scien9fic Consultant to CSICOP • University administra9on
Kevin James saws a man in half
h;p://visualfunhouse.com/videos/kevin-‐james-‐saws-‐a-‐man-‐in-‐half-‐magic-‐trick-‐illusion.html
Amazing Randi Challenge
• Uri Geller’s spoon bending • Susie Co;rell and Ma; Schulein’s spread face-‐down force h;p://magicref.tripod.com/bookssz/willmarthschulien.htm – Illusory sponteneity
– Mul9ple outs
– Confirma9on bias
• Hot coal walking • Psychic surgery
Magic in normal percep9on • Inven9ons of the eye: color, mo9on • Seeing things that aren’t there: Hermann Grid, aZerimages • Failing to see things that are there • Perceptual distor9ons
E.g., how to make something disappear • Stabilize it on the re9na • Camouflage it to look like something else • Camouflage it to blend with background
Illusions: Op9cal versus Perceptual
Black-‐eyed susans under visible versus ultraviolet light
UV Visible
Floaters
Perceptual Illusions: The Lilac Chaser (Jeremy L. Hinton)
h;p://www.michaelbach.de/ot/col_lilacChaser/index.html
Illusions of Brightness
• Seeing spots where there aren’t any • Can I get you to call something white and then black a few minutes later?
Hermann Grid
Scin9lla9ng Grid
Schrauf, Michael, Lingelbach, Bernd & Elke, Wist Eugene (1995)
Simultaneous Contrast
Simultaneous Contrast
h;p://psylux.psych.tu-‐dresden.de/i1/kaw/diverses%20Material/www.illusionworks.com/html/shadow.html
Ted Adelson Shadow Illusion
Mach Bands
Simple neural circuit for seeing Mach Bands
Cornsweet Edges
Illusions of Color
• Wavelength vs. Colors • Color mixtures (addi9ve and subtrac9ve)
• Color aZerimages
Color Vision The rays, to speak properly, are not coloured. In them there is nothing else than a certain Power and Disposi;on to s;r up a Sensa;on of this or that Colour Issac Newton, 1704
Adobe RGB color space sRGB color space
R + G + B
R
G
B
Watercolor Illusion: Pinna, B., Brelstaff, G. and Spillmann, L.: Surface color from boundaries: A new 'watercolor' illusion. Vision Research 41, 2669 -‐ 2676 (2001)
Colored Castle Illusion h;p://www.johnsadowski.com/big_spanish_castle.php
“The grass is always greener on the other side of the fence”
McCollough, Celeste (1965). Color adapta9on of edge-‐detectors in the human visual system. Science, 149, 9, 1115-‐1116.
The McCollough Effect
40
41
43
Color Scission (Metelli)
h;p://www.owlnet.rice.edu/~psyc351/Images/ColorScission.gif
Neon Color Illusion
Also: h;p://www.michaelbach.de/ot/col_neon/index.html
Color Assimila9on and Contrast
Illusions involving Perceptual Organiza9on
Necker Cube
September, 2001 Pomerantz, BISCA, Bolzano, Italy I -‐52
From Rubin
September, 2001 Pomerantz, BISCA, Bolzano, Italy I -‐53
More: h;p://www.graphicdesignblog.org/hidden-‐logos-‐in-‐graphic-‐designing/
From G. Kanizsa
From G. Kanizsa
Colors and Subjec9ve Contours (Kanizsa)
September, 2001 Pomerantz, BISCA, Bolzano, Italy I -‐60
From Wallach
Wallach’s overlooked varia9on: polka dots…
September, 2001 Pomerantz, BISCA, Bolzano, Italy I -‐61
September, 2001 Pomerantz, BISCA, Bolzano, Italy I -‐65
Another example
September, 2001 Pomerantz, BISCA, Bolzano, Italy I -‐66 Slide 66
Illusions of Mo9on
• There are about 10 ways to see something move.
• Only one of them involves images moving across the re9nas!
1. “Real” mo9on 2. Stroboscopic (apparent) mo9on: beta, phi, etc. 3. Induced mo9on (train next to yours starts moving) 4. Autokine9c mo9on 5. Mo9on aZereffect (‘waterfall illusion’): h;p://dogfeathers.com/java/spirals.html
6. Fooling the corollary discharge system 7. Wave mo9on 8. Spa9al distor9ons: Yasmine Gharbaoui (below) 9. Other: op art, Ouche illusion, Akiyoshi Kitaoka's site (below)
Nine s9muli that produce the percep9on of mo9on
Kine9c Depth Effect George Mather’s websites: http://www.lifesci.sussex.ac.uk/home/George_Mather/Motion/demo_ind.html
http://www.lifesci.sussex.ac.uk/home/George_Mather/Motion/
Random Dot Kinematogram
(On dvd)
Common fate: h;p://bit.ly/cQylpw
Johansson’s point-‐light walkers: http://www.biomotionlab.ca/Demos/BMLwalker.html
Breathing square:h;p://www.michaelbach.de/ot/mot_breathingSquare/index.html
Structure from mo9on
Making things disappear: Camouflage
David Gallo on TED: h;p://bit.ly/21Yq1d (4:13)
Random Dot Kinetogram (video)
Illusions of Depth
• How do we see the world in 3D when our re9nas are 2D?
• There are lots of clues to depth. – Some involve our having two eyes – Others don’t.
ViewMaster
Wheatstone stereoscope (1840)
Bela Julesz: Random-‐dot stereograms
Bela Julesz: Random-‐dot Stereograms
Magic Eye
Source: magiceye.com
Magic Eye
False Fusions & the Correspondence Problem
Hollow Faces (Gregory)
h;p://www.michaelbach.de/ot/fcs_hollow-‐face/index.html
Grand Illusion website: The three dragons
Also: Bent card illusion (Mach)
Monocular Depth Cues
Trompe l'oeil sidewalk art
• Julian Beever site
Shepard Boxtops
h;p://psych.rice.edu/neuropsychology/Percep9on/percep9on.html
Source: Roger Shepard, in Kubovy & Pomerantz, Perceptual Organiza9on, 1981
Moon Illusion… since the 7th century BC!
First theory of moon illusion: Ptolemy, 17th century.
Illusions with Spa9al Distor9ons
• Circles look like spirals and vice versa • Parallel lines look non-‐parallel and vice versa
Frazier Spiral Illusion
Café Wall Illusion
h;p://www.michaelbach.de/ot/ang_cafewall/index.html
Ouchi Illusion
Your own, person contrast sensi9vity func9on (MTF)
Illusions with Faces
• We see faces everywhere, even in the clouds and the moon.
• Some people are face-‐blind (prosopagnosia).
Margaret Livingstone, Harvard neurobiologist
Conclusions
• There are lots of perceptual illusions that seem like “magic”
• Many / most of these illusions demonstrate shortcuts our cogni9ve system uses to make percep9on operate more quickly
• We don’t really know what the real world “looks like,” so everything we perceive could be an illusion, at least par9ally!
Thanks
Michael Bach’s illusion site: h;p://www.michaelbach.de/ot/index.html
Akiyoshi Kitaoka's site: h;p://www.ritsumei.ac.jp/~akitaoka/index-‐e.html
Illusionworks: h;p://bit.ly/ch6yRt
Grand Illusions: h;p://www.grand-‐illusions.com/op9calillusions/
Change blindness: h;p://viscog.beckman.illinois.edu/djs_lab/demos.html