Percep Lec

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    VII. Perception

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    Sensation:

    - raw material for perception- started at entry level, data driven

    bottom-up processing

    Perception: top-down processing- concept driven, use preexisting knowledge

    to interpret information.

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    VII. PERCEPTION Recallwe are bombarded with possible energy

    from environment...

    A. To what sensations do we attend? In order to perceive something, we must attend or pay

    attention to it (consciousness).

    Selective Attention:

    Ability to focus awareness on a single stimulus to theexclusion of other stimuli.

    (We focus our awareness on only a limited aspect of

    all that we are capable of experiencing.)

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    B. How do we organize stimuli? We tend to organize stimuli into wholes.

    Origin: Gestalt Psychology

    Gestalt: means whole or form in German.

    Proposed nervous system is predisposed torespond to patterns in stimuli according to

    certain rules. Whole is different from its parts

    Example from videowooden triangle

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    C. FORM PERCEPTION One of these basic rules...

    1. Figure vs. Ground

    To see an image, need to be able to distinguishbetween figure and ground.

    Sometimes, they can be reversible.

    But, at one time, we can focus on only one or other.

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    ging Distance

    an

    ve

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    C. FORM PERCEPTION What stimuli are grouped together?

    2. Grouping- We automatically imply order by grouping

    things together according to certain rules.

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    D. DEPTH & DISTANCE PERCEPTION

    How do we perceive depth/distance?

    - Image on retina is 2-d.

    - Need the brainuses certain cues.

    1. Depth perception:

    a. Binocular Cues:

    Cues for perceiving depth that require both eyes.

    - Retinas receive slightly different images of world.

    - Brain compares those 2 images.

    - Retinal Disparity: difference between 2 images.

    - Key to judging depthSHORT DISTANCES.

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    D. DEPTH OR DISTANCE

    PERCEPTION But, when at a distance, there is very little

    retinal disparity.

    2. Distance perception

    a. Monocular Cues

    Cues for distance that require one eye.

    Example from video.

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    Judging Distance

    Which is closer, the man

    or the house?

    How can you tell?

    -- Interposition

    -- Relative size

    -- Relative height

    -- Linear perspective

    -- Relative Clarity

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    Linear Perspective

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    D. DEPTH OR DISTANCE

    PERCEPTION 3. Nature or nurture?

    When would ability to perceive depth be

    important in terms of development?

    Gibson & Walk (1960):

    Visual Cliff Experiments

    But, is evidence for nurture also. Use it or lose it

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    E. MOTION PERCEPTION Another possible innate ability.

    Speculated to have evolved more for survival

    than other types of perception. Why?

    Brain makes sense of cues:

    Shrinking objects are retreating.

    Enlarging objects are approaching.

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    Perceptual Constancy

    Perceptual constancy:

    We perceive objects as unchanging eventhough the stimuli we receive about those

    objects change.

    Importance of experience and expectations?babies vs. Pygmies

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    Connecting the cues....

    Distance

    Size

    Motion

    Perceptual Constancy

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    Insert slide of Muller-Lyers Illusion

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    INTERPRETATION IN

    PERCEPTION Folk, croak, soak...

    1. Perceptual Set:A mental predisposition to perceive one

    thing and not another.

    - Power of our expectations, predispositionparticularly when interpreting ambiguous

    stimuli.

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    3. Where do our expectations (schemas)

    come from?

    a. Experience

    b. Culture

    Vulnerability to illusions

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    G. INTERPRETATION AND

    PERCEPTIONc. Context

    - Context Effects: We often discern the

    meaning of something by using the context

    in which it is placed.

    - rat/man study- Kulechov effect

    Importance of EXPECTATIONS

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    G. Interpretation in Perception

    How adaptive is our ability to interpret and

    organize stimuli into perceptions?

    4. Perceptual Adaptation:

    In vision, the ability to adjust to an artificially

    displaced or even inverted visual field.

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    Conclusions Perception: The top-down part of understanding

    environment and processing information. Braininterprets and organizes information.

    Amazing feats of grouping stimuli & using cues.

    But that can also cause illusions...

    Individual differences based on experience andexpectations.

    All of these rely on taking in physical energy fromenvironmentsensations.

    Assumption: our experiences are tied to actual,physical events occurring in environment.... see text

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    H. Perception without Sensation?

    ESP -Extrasensory perception:

    Perception without sensory input.

    Types of ESP: Telepathy, Clairvoyance, Precognition

    More than Americans believe in some type ofESP.

    Parapsychologists:

    Psychologists who study psychic phenomenathrough case studies and experiments.

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    H. Perception without Sensation?

    Rhines Research

    Conclusion about ESP:

    No sound evidence for para-psychological

    phenomena

    No single individual who can demonstratepsychic powers to independent investigators

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    Impossible Figures

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    Example:

    Cocktail Party Effect:

    The ability to selectively attend to one voice

    among many.

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