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 constancy
Shape constancy
• For familiar object; image on retina
changes, perceive it as original shape
• Image changes because object moved
Unit VI: Perception: Perceptual constancy
Perceptual constancy
Size constancy
• Objects perceived as having constant
size, even when distance varies
How tall is this person?
Unit VI: Perception: Perceptual constancy
Perceptual constancy
Lightness/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 interpretation
Is our perception learned or are we born with
it?
• Experiments show - both
• Colin Blakemore
• Graham Cooper
• Cambridge - 1970
Unit VI: Perception: Perceptual interpretation
Perceptual interpretation
Is 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 interpretation
Is 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 interpretation
Is 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 interpretation
Is 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 input
Example:
• 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
Context
What is the missing letter(s) in the
below sentence?
The _eel is on the wagon.
Unit VI: Perception: Perceptual set/mental disposition
Context
What 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 Factor
Human 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”