Selective Attention Perception Perceptual Illusions ... kip/120/Lecture_06.pdfChapter 6 2 Perception Selective Attention Perceptual Illusions Perceptual Organization Form Perception Motion Perception Perceptual Constancy 3 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 hazyworm 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 were 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 clocks gotick 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.Co

    urtesy

    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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