A Look at the Science of Illusion Magic, PercepAon, and A@enAon ...

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

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

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

More: h;p://www.graphicdesignblog.org/hidden-‐logos-‐in-‐graphic-‐designing/

From G. Kanizsa

Colors and Subjec9ve Contours (Kanizsa)


From Wallach

Wallach’s overlooked varia9on: polka dots…


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

A Look at the Science of Illusion Magic, PercepAon, and A@enAon ...

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