Organizing the Perceptual World – Module 13

Intro Psych

Mar 8-10, 2010Class #20-21

Gestalt Psychology

Based on the assumption that the whole is greater than the sum of its parts… Basic principles:

Figure-Ground Processing In a noisy environment, we pick out

features that are important (stands out from the rest) this is the figure

The ground is the less relevant stuff

Figure and GroundFigure and Ground

Gestalt Principles of Perceptual Grouping

Having discriminated figure from ground, we then try to organize the figure into a meaningful form

Our minds seem to follow certain rules for grouping stimuli together

Several rules of perceptual organization identified by Gestalt psychologists illustrate their idea that the perceived whole is different from the mere sum of its parts

Gestalt Principles of Perceptual Grouping

Proximity If figures are near each other we tend to group them

together Similarity

If figures are similar to each other we tend to group them together

Continuity We tend to perceive smooth, continuous patterns

rather than discontinuous ones Closure

When a familiar figure is interrupted we imagine the rest of the figure (we finish the picture)

Gestalt Principles of Perceptual Grouping

Texture When basic stimuli have the same texture people tend to

group them together Simplicity

People tend to group features of a stimulus in a way that provides the simplest interpretation of the world

Common Region Elements located within some boundary tend to be

grouped together

Gestalt Principles of Perceptual Grouping Common Fate

Sets of objects that are moving in the same direction and at the same speed are perceived together (example: marching bands)

Connectedness When they are uniformed and linked, we perceive

spots and lines, etc. as a single unit

Depth Perception

This is our ability to transform two-dimensional retinal images into three dimensional perceptions… Seeing objects in three dimensions enables us to

estimate their distance from us

Nativist-Empiricist Debate

Nativists (inborn trait) vs. Empiricists (learned trait) Nativists:

Mind doesn’t rely on experience for meaning but innately organizes sensations into perception

Depth perception emerges too early in life to have been learned

Even adults with limited experience (e.g., handicapped) experience depth

Empiricists: Infants learn depth through feedback from their tactile and

motor experiences They associate eye movements with hand and arm

movements.

Gibson and Walk (1960)

These researchers tried to solve this dispute in their “visual cliff” experiment

Exp 1: human infants

Gibson and Walk (1960)

They designed a “visual cliff”, which was actually a glass-top table

A checkered pattern was positioned close to the glass under one half of the table (the “shallow” side) and far below the glass under the other half (the “deep” side)

Infants between the ages of 6 months and 14 months were placed on the shallow side of the table, and encouraged to crawl over the edge of the visual cliff on to the deep side by being offered toys or having their mothers call them

Most failed to respond to these incentives, suggesting that they possessed at least some of the elements of depth perception

Gibson and Walk (1960)

What do you think was the main criticism of this experiment???

Gibson and Walk (1960)

Experiment 2: Day-old goat Newly hatched chickens

Again, as with the human infants they displayed depth perception

But…

In other studies, new-born chickens are seen pecking at corn that is in fact ten centimeters away until they are forcibly removed, no matter how many times they peck air

Bertenthal & Campos (1978) Nine-month-old infants had faster heart rates

than normal when placed on the deep side, presumably because they were frightened

Held and Hein (1963)

Experiment 1: Kittens raised in darkness until at least six

weeks of age They did not retreat from visual cliff

Held and Hein (1963) Experiment 2:

Placed two kittens in the 'kitten carousel' a device which let one cat move it while the other followed around but was not in control of the motion

This meant that both cats had the same visual experience

The immobile kittens were unable to blink and didn't stretch out their paws when lowered to the ground

However, when allowed free movement they quickly learned the ability, implying that the perception of depth is learned and related to the motor system

So how are we able to develop depth perception? Has to do with the use of certain cues…

Binocular Cues These cues require the use of both eyes

Monocular Cues These cues are available to each eye separately

Binocular Cues: The Pencil Tests Binocular (Retinal) Disparity

The difference between the two retinal images of an object (pencil test #1)

Granrud (1987) – felt that this cue appears to develop after three months of age thereby conflicts with Gibson and Walk (1960)

Binocular Cues: The Pencil Tests Binocular Convergence

A muscular cue that indicates the extent to which our eyes turn inward when we look at an object (pencil test #2)

Goldstein (1999) – we have basic building blocks of convergence at birth but with maturation of our visual systems these further improve with age

Monocular Cues for Perception of Depth and Distance Interposition

Depth cue derived from the overlapping position of objects

Relative Size When object gets larger on the retina we assume they

are closer Textural Gradient

This is provided by our proximity to an object Linear Perspective

Cue provided by the convergence of lines towards a single point of the horizon

Monocular Cues for Perception of Depth and Distance Motion Parallax

The result of changing positions of an object in space due to the motion of the object Accommodation

Feedback we receive from the muscles in the eye that causes the lens to bulge or get thinner (pencil test #3)

Haze Aerial perspective acts as a depth cue over long distances when we are outside

Relative Height We perceive objects higher in our field of vision as farther away (St. Louis Gateway Arch)

Monocular Cues for Perception of Depth and Distance

Light Nearby objects reflect more light in our eyes therefore

given two identical objects, the dimmer one seems farther away

Shadow This also produces a sense of depth consistent with

the assumed light source

Perception of Motion

Looming The rapid expansion of the size of an image so that

it fills the retina If this expansion is equal in all directions then its

coming right at you – if its more to one side it will miss you

Sports Psych – could it be that “expert catchers” unconsciously are able to detect these angles better?

Perception of Motion

Stroboscopic Motion (phi phenomenon) Occurs because of our tendency to interpret as

continuous as series of still images flashed in succession Videotapes show 30 per second – memory of one

is long enough so that we don’t notice any gaps

Perceptual Constancies

Size Constancy A nearer object will have a larger retinal image

but we don't interpret the object as being larger Without size constancy people would appear to

grow as they walked towards you and shrink as they walk away

Our visual system appears to estimate distance and size together

Perceptual Constancies Shape Constancy

Objects viewed from different orientations have different forms but we don't interpret them as different objects

Experience is important determining shape constancies Lightness Constancy

No matter how the amount of light striking an object changes, the object’s perceived brightness does not change

Optical Illusions

A misinterpretation of a visual stimulus… When the "real" and the perceived do not match Illusions mislead us by playing on the ways we

organize and interpret our sensations

“Visual-capture” phenomenon When there is a conflict between visual and other

sensory information, vision seems to dominate or capture the other senses Examples:

When the sound of a movie comes from the projector behind us, we still perceive it as coming from the screen (we “see” the actors talking)

Same as we perceive the voice from the ventriloquist's dummy

Optical Illusions

Which Line Is Longer?Which Line Is Longer?A-C on the Left or A-B on the A-C on the Left or A-B on the

Right?Right?

How many faces do you How many faces do you see?see?

Are the horizontal lines parallel or Are the horizontal lines parallel or

do they slope?do they slope?

Count the black dots...Count the black dots...

What’s going on here?What’s going on here?

How many pandas are there in How many pandas are there in this picture?this picture?

The Impossible TridentThe Impossible Trident

Crossing Circles IllusionCrossing Circles Illusion

Well, we all know how many legs Well, we all know how many legs elephants have...elephants have...

Read this...Read this...

Very strange...Very strange...

Baby In Picture IllusionBaby In Picture Illusion

Expanding Cushion Expanding Cushion IllusionIllusion