SENSATION AND PERCEPTIONModules 16 & 17

PERCEPTUAL ORGANIZATION

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PERCEPTUAL ORGANIZATION

How do we form meaningful perceptions from sensory information?

We organize it. Gestalt psychologists showed that a figure formed a “whole”

different than its surroundings.

4

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

surroundings (ground).

FORM PERCEPTION

Tim

e Savings S

uggestion, © 2003 R

oger Sheperd.

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GROUPING

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

grouping rules.

SIMILARITY

PROXIMITY

CONTINUITY

Our tendency to see patterns and therefore perceive things as belonging together if they form some type of continuous pattern. 

CLOSURE

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GROUPING & REALITY

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

astray.

Both photos by W

alter Wick. R

eprinted from G

AM

ES

Magazine. .©

1983 PCS G

ames L

imited Partnership

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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. Even newborn

animals show depth perception.

Inne

rvis

ions

Visual Cliff Video

PERCEIVING DISTANCE

Monocular Cues those cues which can

be seen using only one eye. 

They include: Relative size Interposition Relative clarity Texture gradient Relative height Relative motion Linear perspective Light and shadow

Binocular Cues those depth cues in

which both eyes are needed to perceive. 

There are two important binocular cues:

Convergence Retinal disparity. 

BINOCULAR CUE: CONVERGENCE

The fact that the closer an object, the more inward our eyes need to turn in order to focus.  The farther our eyes converge, the closer an object appears to be. 

CONVERGENCE VS. ACCOMMODATION

Convergence- Eyes move toward or away from each other Accommodation- Lens moves to bring the vision into focus

Good up to 20 feet

BINOCULAR CUE: RETINAL DISPARITY

The 2.4 inch (6 cm) distance between the two pupils causes us to see two slightly different images of the world. This displacement between the horizontal positions of corresponding images is called binocular disparity.

Our eyes see two images which are then sent to our brains for interpretation, the distance between these two images, or their retinal disparity, provides another cue regarding the distance of the object. Gives us stereoscopic vision

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BINOCULAR CUE

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.

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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.

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MONOCULAR CUES

Interposition: Objects that occlude (block) other objects tend to be perceived as closer.

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.

OVERLAP-INTERPOSITION-SUPERPOSITION-OCCLUSION

those objects covering part of another object is perceived as closer. 

CLARITY-AERIAL-ATMOSPHERIC PERSPECTIVE

Similar to texture, objects tend to get blurry as they get farther away, therefore, clearer or more crisp images tend to be perceived as closer.  

TEXTURE GRADIENT Objects tend to become

smoother as the object gets farther away, suggesting that more detailed textured objects are closer. 

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MONOCULAR CUES

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

those that are lower.

Image courtesy of S

haun P. Vecera, P

h. 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 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.

© T

he New

Yorker C

ollection, 2002, Jack Ziegler

from cartoonbank.com

. All rights reserved.

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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.

From

“Perceiving S

hape From

Shading” by V

ilayaur S

. Ram

achandran. © 1988 by S

cientific Am

erican, Inc. A

ll rights reserved.

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PERCEPTUAL CONSTANCY

Perceiving objects as unchanging even as illumination and retinal

images change.

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Perceiving familiar objects as having consistent color even when changing

illumination filters the light reflected by the object.

COLOR CONSTANCY

Color Constancy

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SIZE-DISTANCE RELATIONSHIP

The distant monster (below, left) and the top red bar (below, right) appear bigger

because of distance cues.

From Shepard, 1990

Alan C

hoisnet/ The Im

age Bank

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SIZE-DISTANCE RELATIONSHIP

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

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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.

Courte

sy E

dwar

d Ade

lson

PERCEPTUAL INTERPRETATION

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PERCEPTUAL INTERPRETATION

Immanuel 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.

How important is experience in shaping ourperceptual interpretation?

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SENSORY DEPRIVATION & RESTORED VISION

After 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).

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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.

Courtesy of R

ichard LeG

rand

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Kittens raised without exposure to horizontal lines later had difficulty

perceiving horizontal bars.

Blakemore & Cooper (1970)

SENSORY DEPRIVATION

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PERCEPTUAL ADAPTATION

Visual ability to adjust to an

artificially displaced visual field, e.g., prism glasses.

Courtesy of H

ubert Dolezal

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PERCEPTUAL SET

A mental predisposition to perceive one thing and not another. What you see in

the center picture 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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Is the “magician cabinet” on the floor or hanging from the ceiling?

CONTEXT EFFECTS

Context can radically alter perception.

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

under a tree.

CULTURAL CONTEXT

Context instilled by culture also alters perception.

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PERCEPTION REVISITED

Is perception innate or acquired?

EXTRASENSORY PERCEPTION

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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.