PERCEPTION: Selective Attention,

Perceptual Organization &

Perceptual Illusion

AP Psychology Chapter 6: Perception

Fall 2014

• Perception is our top-down processing.

• It is the way our brain anticipates, organizes and interprets incoming sensory information.

• Our need to perceive our surroundings, situations, and interactions is automatic and ongoing.

Do you see a woman reading in the light?

Do you see the man’s profile?

SELECTIVE ATTENTION

• At any given moment, our awareness

can only focus on one limited aspect

of all possible experiences.

– Focus your attention on the sound of

the air conditioning or the wireless box

– Now focus your attention on the taste in

your mouth

– Now focus on the colors in the carpet

Types of Selective Attention

• Limits of our attention: – We cannot focus fully on more than one thing at

a time

– It takes time (albeit a short amount) to shift from our focus from one thing to another

• Cocktail Party Effect

• Inattentional blindness

• Change blindness

• Choice blindness

Cocktail Party Effect

• This is our ability to listen to only

one voice at a time while there are

many conversations going on at once.

• In other words, we can’t listen to all conversations simultaneously.

• So if you’re eavesdropping, you’re not concentrating on the person who is talking to you!

Inattentional Blindness

• When we are focusing on one

specific stimulus, we aren’t able to

focus our attention on what else is

going on, and are therefore “blind”

to it.

• Pay close attention!

Change Blindness

• When we are especially focused on

one thing, we can become “blind” to

changes that have occurred around

us or to us!

• Can you detect the change?

Choice blindness

• When people make a choice between 2

things (faces, objects, etc.) they often

haven’t really focused their full attention

on their choice.

• Therefore, if at a later time, they are

shown the opposite face or object and are

told that it was their selection, people

won’t know the different.

• In other words, we make choices all the

time without really thinking about it!

Pop-Out

• A strikingly distinct stimulus that

draws our eye to it.

Can you find the head?

Perceptual Illusion

• Illusions occur when what we think

we see differs from the truth of what

we are seeing

• Illusions help us understand our

expectations and perceptions better

• They reveal how our minds work and

the flaws in the way we perceive.

Visual Illusions

• Poggendorf Illusion

Sound Illusion

• creeping down

PERCEPTUAL ORGANIZATION

• Gestalt:

– A German word

– Whole; organized whole

– Many parts combine to make a whole

– The whole is greater that the sum of it’s

parts

• Our brains are always organizing

incoming sensory information into

meaningful wholes.

Gestalt Examples

Another example

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Form Perception

• When we are looking at lines, shapes

and objects, our brain has several

different ways of organizing the

stimuli:

– Figure-ground:

What’s the object?

And what’s the

surrounding area?

Has your mind put together the “whole” picture?

Form Perception

• Grouping: As the Gestalt theory states, we are always grouping things together to add meaning. When we are identifying forms, we often group them based on:

– How close they are to one another (proximity)

– How much the forms are like one another (similarity)

– Whether the forms fit together to create one continuous form (continuity)

– Whether objects appear to be touching in which case we perceive them as being connected (connectedness)

– And if there are any gaps in the form, our minds just fill them in to complete the shape (closure)

Form Perception

• Grouping: How many different types of grouping can you identify?

• What about in this one?

Depth Perception

• Binocular Cues

– Clues given by both eyes to help us

determine how deep or far away

something is.

• Monocular Cues

– Clues to help us determine depth that

can be identified using just one eye.

Binocular Cues

• Retinal Disparity:

– Each eye has a slightly different

perspective

– Our brains combine the images from

both eyes to determine how far away

the objects are.

• The bigger the difference between the

retinal images, the closer the object is, and

the smaller the different between the eyes’

images, the further away.

Retinal Disparity

• 3-D movies: 2

cameras used to

represent our 2

retinal images.

Binocular Cues

• Convergence:

– Our brains can also tell how close or far away

something is by how much our eye muscles

need to turn inward in order to focus

– A neuromuscular cue

Monocular Cues

• Cues that are available to each eye separately

• The ways we can tell depth in a 2-dimensional painting or photograph.

– Relative size

– Interposition

– Relative clarity

– Texture gradient

– Relative height

– Relative motion

– Linear perspective

– Light and shadow

Relative Size

• We have schemas for all sorts of

objects, people, etc. Therefore, we

assume that certain objects are

roughly the same size (cars,

buildings, etc.)

• When we are looking at 2 similar

objects and one is small and one is

large, we assume that the large one

is closer to us than the smaller one

Relative Size Examples

Relative Size Illusion

Interposition

• If 2 objects are overlapping, the one

in front appears closer to us! (Duh.)

Interposition Illusion

Relative clarity

• Objects that are closer are clearer;

objects that are farther away are

hazier and duller in color

– This is because the light from distant

objects has to pass through more

atmosphere which reduces clarity

Relative Clarity example

Relative Clarity Example

Texture gradient

• The further away an object gets, the

less distinct the texture appears

– Patterns or textures of objects will

appear smaller and closer together the

further away they are.

Texture gradient example

Relative height

• When we look at the horizon, a

painting or a photograph…

– We think objects higher in the image

are farther away and are part of the

“ground” in figure-ground

– We think objects lower in the image are

closer and are the “figure” in figure-

ground

Relative height Illusion

Perceptual Illusion

Relative Motion

• When we are moving and are looking out the window at a fixed point:

– Objects between you and the fixed point will appear to be moving backwards

– Objects beyond the fixed point will appear to be moving in your same direction

– Your brain determines distance based on the speed and direction of perceived movement

Relative Motion example

• Try to concentrate on the moving

landscape instead of the dog. I know,

it’s hard.

Linear perspective

• Parallel lines appear to converge as

they move away from us toward the

horizon.

• The close the lines are, the farther

away we perceive them to be.

Linear Perspective Example

Light and Shadow

• Lighter objects (or parts of objects)

appear closer because nearby

objects reflect more light

• Therefore, objects or parts of

objects that appear dimmer or

darker are perceived as farther

away.

Light and Shadow example

Artists use all the monocular cues to give depth to their art

Relative Clarity

Light and Shadow Linear Perspective

Relative size

Interposition

Texture Gradient

Relative Height

Julian Beever’s Chalk Art

More Amazing Art…

More Amazing Art…

More Amazing Art…

Motion Perception

• Our brain perceives motion when:

– Objects are shrinking (moving away from us)

– Objects are growing (moving toward us)

– Size of objects interfere with our perception’s

accuracy

• Larger objects appear to be moving more slowly that

smaller objects moving at the same speed.

Motion Perception Example

• Phi Phenomenon:

– When lights that are next to each other

blink on and off in succession, we

perceive motion

– Here’s an example

• Stroboscopic movement:

– We perceive a series of slightly

different images strung together as

movement

– A Snowball Fight

Motion Illusion

Motion Illusion

Perceptual constancy

• Shape Constancy: – Our schemas for objects include the shape of the

object and because that is part of our expectation for an object, we “see” that shape even though our perspective may have altered the actual visible shape of the object.

Perceptual constancy

• Size-distance relationship:

– When 2 objects of the same size are placed in

a picture with powerful monocular depth cues, our brains are fooled!

– The depth cues influence our perception of the objects’ sizes.

– To us, the object at the top of image appears farther away and therefore bigger.

– The object of the same size that is at the bottom of the image is perceived as nearer and therefore smaller

Size-Distance Relationship example

Culture & the Müller-Lyer Illusion

• Our environment experiences with buildings, corners and edges have influenced our depth cues.

Lightness Constancy

• Also known as brightness constancy

• We know that an apple is red, so even

when we take an apple out into the

sunshine and it’s bright red, or we take it

into a dimly lit room and it becomes dark

red, our mind doesn’t wonder why the

apple changed shades of red.

• We perceive both shades as the same

because we know the apple’s color stays

constant.

Light constancy

Relative Luminance

The visual system computes brightness and color relative to surrounding objects.

Perceptual Set

• A mental predisposition to perceive

one thing and not another.

• A pre-established expectation that

influences the way we put sensory

stimuli together

• Perceptual sets can be created from

experiences, memories, stereotypes,

etc.

Context Effect

• Information presented before or surrounding an image impacts the way we perceive it.

Which direction is she turning?

http://www.theness.com/images/blogimages/spinning.gif