Perceptual Organization

A group of German psycholgists noticed that when given a cluster of sensations, people tend to organize them into a gestalt (form or whole)

We filter and infer in ways that make sense to us

Human body example: combined value is more valuable than they ever could be on their own

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Form Perception

Organization of the visual field into objects (figures) that stand out from their

surroundings (ground).

2

Tim

e Savings S

uggestion, © 2003 R

oger Sheperd.

Grouping

Proximity-discomfort exampleSimilarity-uncofmrtable with being grouped with people you don’t know

After distinguishing the figure from the ground, our perception needs to organize the figure into a meaningful form using

grouping rules.

Grouping & Reality

Although grouping principles usually help us construct reality, they may occasionally lead us

astray.

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Both photos by W

alter Wick. R

eprinted from G

AM

ES

Magazine. .©

1983 PCS G

ames L

imited Partnership

Depth PerceptionDepth perception enables us to judge distances. Gibson and Walk (1960) suggested that human infants (crawling age) have depth perception. Even newborn animals show depth

perception.*Three dimensions*Depth perception grows with age

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Visual Cliff

Inne

rvis

ions

Binocular Cues: two eyes better than one

Retinal disparity: Images from the two eyes differ. Try looking at your two index fingers when pointing them

towards each other half an inch apart and about 5 inches directly in front of your eyes. You will see a “finger sausage”

as shown in the inset.

*Predator example-peripheral vision

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Monocular Cues

Relative Size: If two objects are similar in size, we perceive the one that casts a smaller retinal image

to be farther away.*Horizontal-vertical illusion-St. Louis Gateway Arch

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Monocular CuesInterposition: Objects that occlude (block)

other objects tend to be perceived as closer.

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Rene M

agritte, The Blank Signature, oil on canvas,

National G

allery of Art, W

ashington. Collection of

Mr. and M

rs. Paul Mellon. Photo by R

ichard Carafelli.

Monocular Cues

Relative Height: We perceive objects that are higher in our field of vision to be farther away than those that are

lower.

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Image courtesy of S

haun P. V

ecera, Ph. D

., adapted from

stimuli that appered in V

ecrera et al., 2002

Monocular Cues

Relative motion: Objects closer to a fixation point move faster and in opposing direction to those objects that are farther away from a fixation

point, moving slower and in the same direction.

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Monocular Cues

Linear Perspective: Parallel lines, such as railroad tracks, appear to converge in the distance. The more the lines converge, the

greater their perceived distance.

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© T

he New

Yorker C

ollection, 2002, Jack Ziegler

from cartoonbank.com

. All rights reserved.

Monocular Cues

Light and Shadow: Nearby objects reflect more light into our eyes than more distant objects. Given two identical objects, the dimmer one appears to

be farther away.

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From

“Perceiving S

hape From

Shading” by V

ilayaur S

. Ram

achandran. © 1988 by S

cientific Am

erican, Inc. A

ll rights reserved.

Perceptual Constancy

Perceiving objects as unchanging even as illumination and retinal images change.

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Color ConstancyPerceiving familiar objects as having consistent color even when

changing illumination filters the light reflected by the object.

*Color comes from object and context

*In a constext that does not vary we maintain color constancy

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Color Constancy

Size-Distance Relationship

The distant monster (below, left) and the top red bar (below, right) appear bigger because of distance cues.*Perceiving an object’s distance gives us cues to its size

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From Shepard, 1990

Alan C

hoisnet/ The Im

age Bank

Size-Distance Relationship

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Both girls in the room are of similar height. However, we perceive them to be of different heights as they stand in the

two corners of the room.

Both photos from S. Schwartzenberg/ The Exploratorium

Lightness Constancy

17 The color and brightness of square A and B are the same.We percieve an object as having a constant lightness even while its illumination varies

Courte

sy E

dwar

d A

delso

n

Perceptual InterpretationImmanuel Kant (1724-1804) maintained that knowledge comes from our inborn ways of

organizing sensory experiences.

John Locke (1632-1704) argued that we learn to perceive the world through our experiences.

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How important is experience in shaping ourperceptual interpretation?

Sensory Deprivation & Restored VisionAfter cataract surgery, blind adults were able to regain sight. These

individuals could differentiate figure and ground relationships, yet they had difficulty distinguishing a circle

and a triangle (Von Senden, 1932).

Born with some aspects of perception but could not by sight recognize

objects that were familiar by touch

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Facial Recognition

After blind adults regained sight, they

were able to recognize distinct features, but

were unable to recognize faces.

Normal observers also show difficulty in facial recognition when the

lower half of the pictures are changed.20

Courtesy of R

ichard LeG

rand

Perceptual Adaptation

Visual ability to adjust to an artificially displaced visual field, e.g., prism glasses.

Humans adapt very quickly!

21

Courtesy of H

ubert Dolezal

Perceptual SetA mental predisposition to perceive one thing and not another. What you see in the center picture is influenced by flanking pictures.

22

From

Shepard, 1990.

Perceptual Set

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(a) Loch ness monster or a tree trunk; (b) Flying

saucers or clouds?

Other examples of perceptual set.We make assumptions based on what we

hearWe form schemas (concepts) through

experiencesFrank Searle, photo Adam

s/ Corbis-Sygm

a

Dick R

uhl

Context Effects

24Is the “magician cabinet” on the floor or hanging

from the ceiling?

Context can radically alter perception. EX: stereotypes of gender

*Studying*Insomnia

Cultural Context

25What is above the woman’s head?

Context instilled by culture also alters perception.

To an East African, the woman sitting is balancing a metal box on her head, while the family is sitting under a tree

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Perception and Motivation and emotion

Motives also matter

Viewers tended to perceive an ample of their “hoped-for category”

Emotions color our social perceptions

Spouses stressful marital events

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Perception Revisited

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Is perception innate or acquired?

Is There Extrasensory Perception?

Perception without sensory input is called extrasensory perception (ESP). A large

percentage of scientists do not believe in ESP.

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Claims of ESP

1. Telepathy: Mind-to-mind communication. One person sending thoughts and the other receiving them.

2. Clairvoyance: Perception of remote events, such as sensing a friend’s house on fire.

3. Precognition: Perceiving future events, such as a political leader’s death.

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Premonitions or Pretensions?

Psychic visions are no more accurate than guesses made by others

Psychics generate hundreds of predictions which increases the odds of an occasional correct guess, which psychics report to the media

Vague predictions can later be interpreted

Coincidences are sure to occur

Horoscopes are so ambiguous so that people can apply them to multiple situations

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