selective attention perception perceptual illusions ...kip/120/lecture_06.pdfchapter 6 2 perception...
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PerceptionPerceptionChapter 6Chapter 6
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Perception
Selective Attention
Perceptual Illusions
Perceptual Organization Form Perception Motion Perception Perceptual Constancy
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Perception
Perceptual Interpretation Sensory Deprivation and
Restored Vision Perceptual Adaptation Perceptual Set Perception and Human Factor
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Perception
The process of selecting, organizing, andinterpreting sensory information, which enables us
to recognize meaningful objects and events.
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Selective AttentionPerceptions about objects change from moment to
moment. We can perceive different forms of theNecker cube; however, we can only pay attention
to one aspect of the object at a time.
Necker Cube6
Example: Cocktail Party Effect
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Inattentional Blindness
Inattentional blindness refers to the inabilityto see an object or a person in our midst.
Simmons & Chabris (1999) showed that halfof the observers failed to see the gorilla-suited assistant in a ball passing game.
Dan
iel S
imon
s, U
nive
rsity
of I
llino
is
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Change Blindness
Change blindness is a form of inattentionalblindness in which two-thirds of individuals
giving directions failed to notice a change in theindividual asking for directions.
© 1998 Psychonomic Society Inc. Image provided courtesy of Daniel J. Simmons.
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Change Blindness Video
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Perceptual Illusions
Illusions provide good examples inunderstanding how perception is organized.Studying faulty perception is as important as
studying other perceptual phenomena.
Which line is longer?
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Tall Arch
In this picture, thevertical dimensionof the arch lookslonger than the
horizontaldimension.
However, both areequal.
Rick Friedman/ Black Star
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Illusion of a Worm
The figure on the right gives the illusion of a blue hazy“worm” when it is nothing else but blue lines identical
to the figure on the left.
© 1981, by perm
ission of Christoph R
edies and Lothar Spillm
ann and Pion Limited, London
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3-D Illusion
It takes a great deal of effort to perceive this figure intwo dimensions.
Reprinted w
ith kind permission of Elsevier Science-N
L. Adapted from
H
offman, D
. & R
ichards, W. Parts of recognition. C
ognition, 63, 29-78
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Escher Drawing
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Organization of the visual field into objects(figures) that stand out from their surroundings
(ground).
Form Perception
Time Savings Suggestion, ©
2003 Roger Sheperd.
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Perceptual Organization
When vision competes with our othersenses, vision usually wins – a phenomena
called visual capture.
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Visual Capture Examplee.g., movie projector voices (vision overtakes hearing)
This can be true with other senses as welle.g., finger touch and various tones; feeling like we’re moving when
simply watching an action movie18
Sensory and Perception BlendHow do we form meaningful perceptions from
sensory information?
We organize it!Gestalt psychologists showed that a figure formed
a “whole” different than its surroundings.
Our brains do a heck of a lot more than just merelyregister information about the world!
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Gestalt Psychologists: Grouping
After distinguishing the figure from the ground,our perception needs to organize the figure into
a meaningful form using grouping rules.
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Grouping & Reality
Although grouping principles usually help us constructreality, they may occasionally lead us astray.
Both photos by W
alter Wick. R
eprinted from G
AM
ES M
agazine. .© 1983 PC
S Gam
es Limited Partnership
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Patterns
• Naturally we look forpatterns in life
• In addition to visualpatterns, we alsoconcoct patterns withour other senses
e.g., We tend to hear clock’s go“tick TICK tick TICK”, but inreality, the sounds are thesame-“tick tick tick tick”,
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Depth Perception
Visual Cliff
Depth perception enables us to judge distances.Gibson and Walk (1960) suggested that human
infants (crawling age) have depth perception. Evennewborn animals show depth perception.
Inne
rvisi
ons
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Binocular Cues:Need the use of two eyes
Retinal disparity: Images from the two eyes differ. Trylooking at your two index fingers when pointing them
towards each other half an inch apart and about 5 inchesdirectly in front of your eyes. You will see a “finger
sausage” as shown in the inset.
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Binocular Cues
Convergence: Neuromuscular cues. When two eyes moveinward (towards the nose) to see near objects and outward
(away from the nose) to see faraway objects.*Two eyes are better than one!
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Monocular Cues:Can use eyes together or either eye alone
Relative Size: If two objects are similar in size, weperceive the one that casts a smaller retinal image
to be farther away.
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Monocular Cues
Interposition: Objects that occlude (block) otherobjects tend to be perceived as closer.
Rene M
agritte, The Blank Signature, oil on canvas, N
ational Gallery of A
rt, Washington. C
ollection of M
r. and Mrs. Paul M
ellon. Photo by Richard C
arafelli.
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Monocular Cues
Relative Clarity: Because light from distant objectspasses through more light than closer objects, we
perceive hazy objects to be farther away thanthose objects that appear sharp and clear.
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Monocular Cues
Texture Gradient: Indistinct (fine) texture signalsan increasing distance.
© Eric Lessing/ A
rt Resource, N
Y
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Monocular Cues
Relative Height: We perceive objects that are higher in ourfield of vision to be farther away than those that are lower.
Image courtesy of Shaun P. V
ecera, Ph. D.,
adapted from stim
uli that appered in Vecrera et al., 2002
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Monocular Cues
Relative motion: Objects closer to a fixation point movefaster and in opposing direction to those objects that are
farther away from a fixation point, moving slower and inthe same direction. This is how we compute objects’
distances.
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Monocular Cues
Linear Perspective: Parallel lines, such as railroadtracks, appear to converge in the distance. The
more the lines converge, the greater theirperceived distance.
© The N
ew Y
orker Collection, 2002, Jack Ziegler from
cartoonbank.com. A
ll rights reserved.
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Monocular Cues
Light and Shadow: Nearby objects reflect more light intoour eyes than more distant objects. Given two identical
objects, the dimmer one appears to be farther away.
From “Perceiving Shape From
Shading” by Vilayaur
S. Ram
achandran. © 1988 by Scientific A
merican, Inc.
All rights reserved.
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Motion PerceptionMotion Perception: Objects traveling towards usgrow in size and those moving away shrink in
size. The same is true when the observer moves toor from an object.
e.g., driving
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Apparent Motion
Phi Phenomenon: When lights flash at a certainspeed they tend to present illusions of motion.Neon signs use this principle to create motion
perception.
Two lights flashing one after the other.One light jumping from one point to another: Illusion of motion.
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Perceptual Constancy
Perceiving objects as unchanging even asillumination and retinal images change. Perceptualconstancies include constancies of shape and size.
Shape Constancy 36
Size Constancy
Stable size perception amid changing size of thestimuli.
Size Constancy
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Size-Distance Relationship
The distant monster (below, left) and the top redbar (below, right) appear bigger because of
distance cues.
From Shepard, 1990
Alan C
hoisnet/ The Image B
ank
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Size-Distance Relationship
Both girls in the room are of similar height.However, we perceive them to be of differentheights as they stand in the two corners of the
room.
Both photos from S. Schwartzenberg/ The Exploratorium
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Ames Room
The Ames room is designed to demonstrate the size-distance illusion.
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Lightness Constancy
The color and brightness of square A and B are the same.Cou
rtesy
Edw
ard A
delso
n
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Perceiving familiar objects as having consistentcolor even when changing illumination filters
the light reflected by the object.
Color Constancy
Color Constancy 42
Visual Illusions Video
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Perceptual Interpretation
Immanuel Kant (1724-1804) maintained thatknowledge comes from our inborn ways of
organizing sensory experiences.
John Locke (1632-1704) argued that we learn toperceive the world through our experiences.
How important is experience in shaping ourperceptual interpretation?
e.g., Amadou Diallo and police incident
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Video Time
What happens when we have sensationwithout perception?
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Restored Vision
After cataract surgery,blind adults were ableto regain sight. These
individuals coulddifferentiate figure andground relationships,yet they had difficultydistinguishing a circle
and a triangle(Von Senden, 1932).
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Facial Recognition
After blind adultsregained sight, they wereable to recognize distinctfeatures, but were unable
to recognize faces.Normal observers alsoshow difficulty in facial
recognition when thelower half of the pictures
are changed.
Courtesy of R
ichard LeGrand
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Kittens raisedwithout exposure tohorizontal lines later
had difficultyperceiving horizontal
bars.
Blakemore & Cooper (1970)
Sensory Deprivation
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Perceptual Adaptation
Visual ability to adjustto an artificially
displaced visual field,e.g., prism glasses.
Courtesy of Hubert D
olezal
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Perceptual Set
A mental predisposition to perceive one thingand not another. What you see in the centerpicture is influenced by flanking pictures.
From Shepard, 1990.
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(a) Loch ness monster or a tree trunk;(b) Flying saucers or clouds?
Perceptual Set
Other examples of perceptual set.
Frank Searle, photo Adam
s/ Corbis-Sygm
a
Dick R
uhl
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Children's schemas represent reality as well as theirabilities to represent what they see.
SchemasSchemas are concepts that organize and
interpret unfamiliar information.Schemas develop through experience.
Courtesy of Anna Elizabeth V
oskuil
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Students recognized a caricature of ArnoldSchwarzenegger faster than his actual photo.
Features on a Face
Face schemas are accentuated by specificfeatures on the face.
Kieran Lee/ FaceLab, D
epartment of Psychology,
University of W
estern Australia
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Eye & Mouth
Eyes and mouth play a dominant role in facerecognition.
Courtesy of C
hristopher Tyler
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Is the “magician cabinet” on the floor or hanging from theceiling?
Context Effects
Context can radically alter perception.
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To an East African, the woman sitting is balancing a metalbox on her head, while the family is sitting under a tree.
Cultural Context
Context instilled by culture also altersperception.
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Perception Revisited
Is perception innate or acquired?
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Perception & Human Factors
Human Factor Psychologists design machines thatassist our natural perceptions.
The knobs for the stove burners on the right are easier tounderstand than those on the left.
Photodisc/ P
unchstock
Courtesy of G
eneral Electric
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Human Factors & Misperceptions
Understanding human factors enables us todesign equipment to prevent disasters.
Two-thirds of airline crashes caused by human error arelargely due to errors of perception.
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Human Factors in Space
To combat conditions of monotony, stress, andweightlessness when traveling to Mars, NASA
engages Human Factor Psychologists.
Transit Habituation (Transhab), NASA 60
Is There Extrasensory Perception?
Perception without sensory input is calledextrasensory perception (ESP). A large percentage
of scientists do not believe in ESP.
Claims of ESP Premonitions or Pretensions Putting ESP to Experimental Test
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Claims of ESPParanormal phenomena include astrological
predictions, psychic healing, communication withthe dead, and out-of-body experiences, but most
relevant are telepathy, clairvoyance, andprecognition.
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Claims of ESP
Telepathy: Mind-to-mind communication. Oneperson sending thoughts and the otherreceiving them.
Clairvoyance: Perception of remote events,such as sensing a friend’s house on fire.
Precognition: Perceiving future events, such asa political leader’s death.
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Putting ESP to Experimental Test
In an experiment with 28,000 individuals,Wiseman attempted to prove whether or not onecan psychically influence or predict a coin toss.
People were able to correctly influence or predicta coin toss 49.8% of the time.
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Premonitions or Pretensions?Can psychics see the future?
Can psychics aid police inidentifying locations of
dead bodies? What aboutpsychic predictions of the
famous Nostradamus?
The answers to thesequestions are NO!
Nostradamus’ predictionsare “retrofitted” to events
that took place after hispredictions.
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Review SessionReview Sessionfor Exam 2for Exam 2
Wednesday, Feb 13Wednesday, Feb 13thth
5:30-6:30pm5:30-6:30pmLocation: In this roomLocation: In this room
Bring Questions!Bring Questions!