Unit VI: Perception: Perceptual constancy Perceptual constancy Stimuli changes, object perceived to stay the same In other words: Image on retina changes,

Unit VI: Perception: Perceptual constancy

Perceptual constancy

•Stimuli changes, object perceived to stay the same• In other words:• Image on retina changes, but brain perceives image as being constant/unchanging •Stimuli changes, but percept remains the same•Sensation changes, perception doesn’t

Unit VI: Perception: Perceptual constancy

Perceptual constancyShape constancy

•For familiar object; image on retina changes, perceive it as original shape• Image changes because object moved

Unit VI: Perception: Perceptual constancy

Perceptual constancySize constancy

•Objects perceived as having constant size, even when distance varies

How tall is this person?

Unit VI: Perception: Perceptual constancy

Perceptual constancyLightness/brightness constancy

•Object perceives to have constant color even when illumination varies•Frequency doesn’t change, amplitude changes

Relative luminance: Amount of light an object reflects relative to its surrounding

Unit V: Sensation – Color vision

Color vision – theories

Color constancy•How we see color influenced by surroundings & context •Object in different surrounding, color may appear different

Inner squares all the same color gray?

Unit VI: Perception: Perceptual constancy

Perceptual constancy

Lightness/Brightness Constancy vs. Color Constancy • Lightness/brightness constancy: • Level of light changes• Image on retina different• Colors perceived the same

• Color constancy:• Surroundings change• Image on retina the same• Color perceived differently

Unit VI: Perception: Perceptual constancy

Illusions - Perceptual Constancy & Monocular Cues

•Constancy: • image on retina different•brain perceives images as unchanging

•Most cues: • images on retina different•brain perceives images as different

Unit VI: Perception: Perceptual interpretation

Perceptual interpretationIs our perception learned or are we born with it?

•Experiments show - both•Colin Blakemore•Graham Cooper•Cambridge - 1970

Unit VI: Perception: Perceptual interpretation

Perceptual interpretationIs our perception learned or are we born with it?

•Kittens – blinders from birth until six months (critical period):•Visual cortex didn’t develop•Eye works properly – transducts, etc.•Visual cortex can’t process

Unit VI: Perception: Perceptual interpretation

Perceptual interpretationIs our perception learned or are we born with it?

•Kittens – blinders from six months until year old:•Little effect•Period of adaptation; no permanent effect

Unit VI: Perception: Perceptual interpretation

Perceptual interpretationIs our perception learned or are we born with it?

•Kittens – blinders from birth until six months: one eye•Little effect•Period of adaptation; no permanent effect

Unit VI: Perception: Perceptual interpretation

Perceptual interpretationIs our perception learned or are we born with it?

Kittens – environment with vertical lines (critical period)•Feature detection - horizontal lines don’t develop

Unit VI: Perception: Perceptual interpretation

Perceptual adaptation • Ability to adapt to changed visual inputExample:•New glasses •Glasses - images upside down•Glasses - images left to right• Period of adaptation

Unit VI: Perception: Perceptual set/mental disposition

Perceptual set/mental disposition

•Mental predisposition to perceive things a certain way•Varies, person-to-person•Based on several factors

Unit VI: Perception: Perceptual set/mental disposition

Perceptual set/mental disposition

1) Schema•Assimilation

2) Context

3) Anticipation•We see what we expect to see

Unit VI: Perception: Perceptual set/mental disposition

ContextWhat is the missing letter(s) in the below sentence?

The _eel is on the wagon.

Unit VI: Perception: Perceptual set/mental disposition

ContextWhat is the missing letter(s) in the below sentence?

The _eel is on the orange.

Loch Ness Monster or a Tree Trunk?

Champy or a Tree Trunk?

acoindrcg to an Eslnigh usintreviy sdtuy the oerdr of ltteers in a word donset mettar the only tnhig ttahs imtorpnat is that the fsirt and last letetr of every word is in the crrocet potsoiin The rset can be jlembud and one is sltil albe to read the txet wuohtit dilffcutiy

Anticipation

Anticipation

Anticipation

Unit VI: Perception: Perceptual constancy

Illusions - Perceptual Constancy & Monocular Cues

•With many illusions: combination of cues & constancy trick the brain• I.e. images on retina is same, but brain perceives them differently because of cues

Unit VI: Perception: Perceptual constancy

Illusions - Perceptual Constancy & Monocular Cues

Shepard’s table•Same images on retina; brain perceives them differently •Relative height

Unit VI: Perception: Perceptual constancy

Illusions - Perceptual Constancy & Monocular Cues

Ponzo Illusion & Shepard’s Monsters

•Both images same size (same image on our retinas)•Linear perspective & relative height: second monster/bar should be further away•So should be smaller (relative size) •But it’s not, so brain perceives it as larger (size constancy)

Unit VI: Perception: Perceptual constancy

Illusions - Perceptual Constancy & Monocular Cues

Moon illusion•Moon close to horizon appears larger•Shrinks as it rises•Variant of Ponzo Illusion •Relative height + relative size

Unit VI: Perception: Perceptual interpretation

Perception and the Human FactorHuman factors psychology• Help design appliances machines, settings,

etc. that fit our natural perceptions • Explores how :• people and machines interact •machines/technology can be adapted to human behaviors

• “User friendly”