Perceptual Organization

Unit 3 – RG 4eModified PowerPoint from: Aneeq Ahmad -- Henderson State University. Worth Publishers © 2007

Perceptual Illusions

To understand how perception is organized,

illusions provide good examples. It is as good to

study faulty perception as other perceptual

phenomena.

Line AB is longer than line BC.

Tall Arch

Vertical dimension

of the arch looks

longer than the

horizontal

dimension when

both are equal.

Rick Friedman/ Black

Star

Perceptual Organization

When vision competes with other senses vision usually wins – a phenomenon called visual

capture.

How do we form meaningful perceptions from sensory information?

We organize it!

Gestalt psychology helps us organize information into meaningful wholes…

but remember…the “whole is different from the sum of it’s parts”

Figure-Ground

Organization of the visual field into objects

(figures) that stand out from their surroundings

(ground).

Time Savings Suggestion, © 2003 Roger

Sheperd.

Gestalt Grouping

Having discriminated figure from ground our

perception needs to organize figure into

meaningful form using grouping rules.

Grouping & Reality

Usually grouping principles help us construct

reality but at times lead us astray.

Both photos by Walter Wick. Reprinted from

GAMES

Magazine. .© 1983 PCS Games Limited

Partnership

Depth PerceptionDepth perception enables us to judge distances. Gibson and Walk (1960) suggested that human

infants (crawling age) have depth perception. Even new born animals show depth perception.

Visual Cliff

Innervision

s

Monocular Cues

Interposition: Objects that occlude (block) other

objects tend to be perceived as closer.

Rene Magritte, The Blank Signature, oil on

canvas,

National Gallery of Art, Washington. Collection of

Mr. and Mrs. Paul Mellon. Photo by Richard

Carafelli.

Monocular Cues

Linear Perspective: Parallel lines like rail road

tracks, appear to converge with distance. The

more the lines converge, the greater their

perceived distance.

Monocular Cues

Relative Size: If two objects are similar in size, we

perceive one that casts a smaller retinal image as

farther away.

Monocular Cues

Relative Height: We perceive objects higher in our

field of vision as farther away.

Image courtesy of Shaun P. Vecera, Ph. D.,

adapted from stimuli that appered in Vecrera et al.,

2002

Monocular Cues

Texture Gradient: Indistinct (fine) texture signals

increasing distance.

© Eric Lessing/ Art Resource,

NY

Binocular CuesConvergence: When two eyes move inward (towards the nose) to see near objects, and

outward (away from the nose) to see far away objects…object is perceived as closer the more

eyes turn inward

Binocular Cues

Retinal disparity: Images from the two eyes differ…the greater the difference between the two objects, the closer

the objectTry looking at your two fingers half an inch apart about 5 inches away.

You will see a “finger sausage” as shown in the inset.

Perception of Movement

Stroboscopic motion: our tendency to perceive

motion in a series of slightly varied still images

flashed in rapid succession

Perception of Movement

Phi Phenomenon: When lights flash at certain

speed 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.

Perceptual Constancy

Perceiving objects as unchanging even as

illumination and retinal image change. Perceptual

constancies include constancies of shape and

size.

Shape

Constancy

Size Constancy

Stable size perception amid changing size of the

stimuli.

Size

Constancy

Size-Distance Relationship

Moon Illusion

What makes this happen?

Cues to the objects’ distances at the horizon make the Moon

behind them seem farther away than the moon in the

night’s sky.

Actually…there are various explanations, yet no ONE

“right” answer

Size-Distance Relationship

The distant monster and the top red bar appear bigger because of distance cues.

Ponzo Illusion

From Shepard,

1990

Alan Choisnet/ The Image

Bank

Depth Perception Webquest

1. Go to class website, under Unit 4, Perceptual Organization Notes, click on “Depth Perception Webquest- website”

2. Go through the web page, filling in the chart a quick description of each depth cue

3. Come up with your own example of each depth cue- must be your own, not from the website, book, or notes

Size-Distance Relationship

Muller-Lyer Illusion

Are these vertical lines the same length?

Size-Distance Relationship

Both girls in the room are of similar height,

however we perceive them of different heights

as they stand in the two corners of the room.

Both photos from S. Schwartzenberg/ The

Exploratorium

Ames Room

An Ames room is designed to give size-distance

illusion.

Visual Illusions…

Straight lines or bowed? Stationary or moving?

Visual Illusions…

A spiral right?How many people/faces

do you see?

Visual Illusions…

Which line matches with C?

It’s actually B…

Poggendorf Illusion

Old woman or young woman?

Visual Illusions…

These are on drawn on flat surfaces (sidewalks)!

Visual Illusions…

Julian Beever has made pavement drawings for over ten years. He has

worked in the U.K., Belgium, France, The Netherlands, Germany, the

USA and Australia.

Visual Illusions…

For more go to…

http://users.skynet.be/J.Beever/pave.htm