Download Psych 110 - Kansas State University

Sensation & Perception
On chapters 7 & 8
Gray 4th edition
© Kip Smith, 2003
Sensation - Topics
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Basics
Taste and Smell
Touch and Pain
Hearing
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The ear and cochlea
Getting aural information to the brain
Vision
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The eye and retina
Getting visual information to the brain
© Kip Smith, 2003
Perceptual Basics
Thresholds
Top down & bottom up processing
© Kip Smith, 2003
Sensation
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≠
The picking up of
information from the
environment and the
body
Perception
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The transformation of
input signals into
action potentials
We experience 5
modalities of external
sensation
© Kip Smith, 2003
Coming aware of
information from the
environment
The transformation of
action potentials from
multiple modalities
into a coherent
representation of the
environment
Basics - Absolute thresholds
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The limits of perception
The lowest level of a stimulus, X, that
provokes a response from the sensory
system
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Vision: the faintest detectable light
Sound: the quietest detectable sound
© Kip Smith, 2003
Difference thresholds
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The limits to the perception of change
The smallest increment of a stimulus, DX, that
provokes a response from the sensory system
Weber’s Law
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Pressure:
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© Kip Smith, 2003
Q = Dc/c
X = the weight of some object
DX = the smallest weight that makes that object feel
heavier
Another threshold
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Vision: We see 24 “frames” per second
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Anything faster appears continuous
Movies project at 32 (?) frames per second and
convince us the motion is continuous
© Kip Smith, 2003
Subliminal signals
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Signals that are below threshold
Question: Can we be influenced by
signals that are below threshold?
© Kip Smith, 2003
Top Down
vs. Bottom Up
Top Down
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From the whole to the
parts
Perception is driven by
context or expectation
© Kip Smith, 2003
Bottom Up
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From the parts to the
whole
Perception is driven by
features of the
stimulus
What is this?
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Describe it
© Kip Smith, 2003
Please read this aloud
THE CAT IN THE HAT
© Kip Smith, 2003
An ancient Buddhist parable
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It was six men of Indostan, to learning much inclined,
Who went to see the elephant (though all of them were blind),
That each by observation might satisfy his mind.
The first approached the elephant, and, happening to fall
Against his broad and burly side, at once began to call:
"I see," said he, "the elephant is very like a wall!"
The second, feeling of the tusk, cried, "Ho! What have we here
So very round and smooth and sharp? To me 'tis mighty clear
This wonder of an elephant is very like a spear!"
© Kip Smith, 2003
Top down or bottom up ?
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The third approached the animal, and, happening to take
The squirming trunk within his hands, thus boldly up and spake,
"I see," said he, "the elephant is very like a snake!"
The fourth reached out his eager hand and felt about the knee:
"What most this wondrous beast is like is mighty plain, " said he,
"'Tis clear enough the elephant is very like a tree!"
The fifth, who chanced to touch the ear, said, "E'en the blindest
man
Can tell what this resembles most. Deny the fact who can,
This marvel of an elephant is very like a fan!"
© Kip Smith, 2003
End of the parable
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The sixth no sooner had begun about the beast to grope,
Than, seizing on the swinging tail that fell within his scope,
"I see," said he, "the elephant is very like a rope!"
And so these men of Indostan disputed loud and long,
Each in his own opinion exceeding stiff and strong,
though each was partly in the right, and all were in the wrong!
So oft in group endeavors, the members of the team
Rail on in utter ignorance of what each other mean,
As if it were an elephant not one of them has seen.
© Kip Smith, 2003
Taste and Smell
The chemical senses
Gatekeepers to the insides
© Kip Smith, 2003
Taste and Smell
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Intimately related
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Most of the flavor of food is sensed not in
the mouth but in the nose
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Sensory interaction
Pinch your nose and apple = potato
Smell is unique
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No thalamic waystation
© Kip Smith, 2003
Taste
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Signal
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Receptors
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Spontaneously
regenerate every two
weeks
Stuff that enters your
body
Taste buds on tongue
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Neural pathway
© Kip Smith, 2003
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Sweet
Salt
Bitter
Sour
Thalamus to the
medulla
Smell
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Signal
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Receptors
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Neural pathway
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© Kip Smith, 2003
Stuff that enters your
body
Little hairs in the back
of the nose
Directly to the
temporal lobe: no
thalamic waystation
Smell
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Each receptor
responds to a limited
number of chemicals
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There are thousands of
receptors & thousands of
chemicals
There is no one-to-one
dedicated circuit
© Kip Smith, 2003
Smell
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The receptors in your nose are every bit
as good as those in your dog’s nose
Why does your dog have a better sense of
smell?
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The dog has a thousand times as many
sensors
© Kip Smith, 2003
Pheromones
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Chemical communication
Sexual attraction / receptivity
© Kip Smith, 2003
Touch and Pain
© Kip Smith, 2003
Touch ≠ Pain
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Touch is for exploring the environment
Pain is a warning signal that something is
wrong
Leprosy is a disease that, among other
things, kills the nerves that carry the pain
signal
© Kip Smith, 2003
Touch
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The skin has 4 different kinds of pressure
sensors specialized to sense different type
of pressure
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Broad, diffuse pressure
Tapping
Stretching
Vibration
Thermoreceptors are different sets of cells
© Kip Smith, 2003
Touch
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The density of pressure sensors varies
Why?
Lots on the tips of fingers, lips
Few on the calf
© Kip Smith, 2003
Gate Control Theory of Pain
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Small fibers carry the pain signal
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Activity in the small fibers opens a “gate,” and
you sense pain
Large fibers carry all other pressure
signals
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Activity in the large fibers closes the “gate,”
suppressing the pain
© Kip Smith, 2003
Hearing
From Sound Waves to the Cortex
© Kip Smith, 2003
Ear Workings
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Sound waves
Ear drum (tympanic membrane)
Middle ear
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Hammer, anvil, stirrup
Inner ear
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Cochlea
Basilar membrane
Hair cells
© Kip Smith, 2003
Properties of Sound Waves
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Wavelength
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The distance between
adjacent pressure peaks
or troughs
Pitch or tone or notes
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© Kip Smith, 2003
Which notes travel
further? High or low?
Low notes
Why?
The lower the note,
the longer the
wavelength
Properties of Sound Waves
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Amplitude
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The height between a
pressure peak and the
adjacent trough
Loudness
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© Kip Smith, 2003
Is there such a thing
as too loud?
Yes
Why?
The receptors - hair
cells in the cochlea are very sensitive and
can be easily damaged
How do we … ?
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Determine Loudness
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Encoded by the number of neurons firing
Localize Sounds
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Two ears:
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© Kip Smith, 2003
Sound reaches the two ears differently
time differences
loudness differences
Hearing Pitch - 2 Theories
Place Theory
Frequency Theory
© Kip Smith, 2003
Place theory
Frequency theory for pitch
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Neurons fire at same rate as the
frequency of the sound.
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Example:
If a sound wave has 100 pressure peaks per
second (100 Hz), then the action potentials will
fire 100 times per second.
© Kip Smith, 2003
So which is right?
Place Th. or Frequency Th.?
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High Frequencies
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V. Low Frequencies
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Place theory
Both!
Frequency theory
Everything else
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Some combination of the two
© Kip Smith, 2003
Hearing, Summary
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Signal
Signal processing
apparatus
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Soundwave
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Ear
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Eardrum
Middle ear bones
Inner ear, cochlea
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Receptors/ transducers
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Hair Cells
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Neural pathway
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Auditory nerve
© Kip Smith, 2003
Vision & Hearing
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Both the optic and auditory nerves project to the
thalamus
Information from the right (left) side goes to the
left (right) thalamus and to the left (right)
hemisphere of the cortex
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Perceptual information is processed on the contralateral
side
The auditory cortex is in the temporal lobe
The visual cortex in the occipital lobe
© Kip Smith, 2003
Vision
From Photons to Action Potentials
© Kip Smith, 2003
The visual stimulus
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Photons
Light that reflects off a surface in the
environment and then passes through the
lens of your eye
© Kip Smith, 2003
Eyeball
© Kip Smith, 2003
Parts of the eye
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Pupil
Iris
Lens
Humors
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Retina
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Fovea
Optic nerve
Blind spot
© Kip Smith, 2003
Topics
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Distribution of
photoreceptors
Receptive fields
The Retina
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The back of the eye is called the retina
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The retina is composed of photoreceptors:
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rods and cones
and neurons:
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bipolar
horizontal
ganglia
© Kip Smith, 2003
The retina is part
of the brain
Rods and Cones
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Rods and cones are photoreceptors
They transduce (= convert) light into
action potentials
They convert photons into neural activity
© Kip Smith, 2003
Structure of the retina
How the transduction works
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A photon stimulates a rod or cone
The rod or cone generates a cascade of
chemical reactions that produce a voltage
The voltage triggers an action potential in
the attached neuron (a bipolar cell)
© Kip Smith, 2003
Visual information
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The action potential is information of the
existence of light at a specific location on
the retina
Each location on the retina provides
information about a specific location in the
environment
The action potential is information about
surfaces in the environment
© Kip Smith, 2003
The transmission of information
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The bipolar cell sends a signal to a
ganglion cell (another type of neuron)
The ganglion cell sends the signal via the
optic nerve to the thalamus (the sensory
way station)
© Kip Smith, 2003
Differences between
rods and cones
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Sensitivity vs. Resolution:
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Rods share ganglion cells
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Cones do not
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high sensitivity, low resolution
low sensitivity, high resolution
Color
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Rods are insensitive to color
There are 3 types of cones, sensitive to 3
different parts of the color spectrum
© Kip Smith, 2003
Color Vision - 2 Theories
© Kip Smith, 2003
Tri-Chromatic Theory - Helmholtz
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Herr Helmholtz (1860s) claimed human
vision uses three color receptors
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sensitive to either red, green, blue
and constructed all intermediate colors
from combinations of the basic three
© Kip Smith, 2003
Tri-Chromatic Theory - Helmholtz
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Herr Helmholtz (1860s) claimed human
vision uses three color receptors
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sensitive to either red, green, blue
and constructed all intermediate colors
from combinations of the basic three
In the 20th century, the human was found
to have three types of cones
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sensitive to either red, green, or blue
© Kip Smith, 2003
Opponent Process Theory Hering
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Herr Hering (1870s) said the human
visual system uses three channels with
opposing processes
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Red vs. Green channel
Yellow vs. Blue channel
Black vs. White channel
© Kip Smith, 2003
Selectively connected ganglia
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Research has demonstrated that there are
pairs of ganglia for each receptive field in
the fovea
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One of the pair is activated by light in the
green part of the spectrum
The other is activated by light in the red
There are similar pairs of ganglia for
yellow & blue and for rods (black or white)
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for each and every foveal field
© Kip Smith, 2003
A problem with the Opponent
Process Theory
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How do we see
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Purple?
Pink?
Turquoise?
Brown?
Shades of gray?
© Kip Smith, 2003
Getting the signal to the cortex
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Information in the left visual field is seen
on the right side of both retinas.
Ganglia on the right (left) side of the
retina project to the right (left)
hemisphere
Information in the world in processed in
the contralateral cortical hemisphere
© Kip Smith, 2003
The flow of visual information
Vision, Summary
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Signal
Signal processing
apparatus
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Photon
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Eye
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Receptors/ transducers
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Neural pathway
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© Kip Smith, 2003
Pupil
Lens
Rods & cones
Bipolar, horizontal &
ganglion cells, optic
nerve
Perception
Topics
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Gestalt Psychology
Depth Perception
Perceptual Constancy
© Kip Smith, 2003
Gestalt Psychology
© Kip Smith, 2003
Figure/Ground
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The visual system
must distinguish an
object from its
surroundings
The object is known as
the “figure”
The surroundings are
known as the “ground”
© Kip Smith, 2003
Grouping Principles
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The visual system must also group pieces
of information together
Five grouping principles:
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Proximity
Similarity
Continuity
Closure
Connectedness
© Kip Smith, 2003
Proximity
What do you see?
Observation:
We tend to group together
items that are close together
This is the
Gestalt Principle of Proximity
© Kip Smith, 2003
Similarity
What do you see?
Observation:
We tend to group together
items that are physically
similar.
This is the
Gestalt Principle of Similarity
© Kip Smith, 2003
Continuity
What do you see?
Observation:
We tend to organize smooth
continuous patterns rather
than discontinuous patterns
This is the
Gestalt Principle of Continuity
© Kip Smith, 2003
Closure
What do you see?
Observation:
We tend to fill in gaps
to make complete objects
This is the
Gestalt Principle of Closure
© Kip Smith, 2003
Connectedness
What do you see?
Observation:
We tend to group things
that are connected
This is the
Gestalt Principle of
Connectedness
© Kip Smith, 2003
Depth Perception
© Kip Smith, 2003
Depth Perception
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Definition: seeing in 3-D space
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Seeing depth takes advantage of both:
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Binocular cues
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Require both eyes
Monocular cues
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© Kip Smith, 2003
Requires only one eye
Binocular Cues
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Retinal Disparity
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The eyes receive slightly different views of the
world
Convergence
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The eyes turn more toward the center as
objects move closer
© Kip Smith, 2003
Monocular Cues
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Relative size
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Relative motion
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Interposition
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Linear perspective
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Relative clarity
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Texture gradient
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Relative height
© Kip Smith, 2003
Implied direction of
illumination (relative
brightness)
Relative Motion
Far objects appear
to move with you;
albeit at a slower rate.
Fixation
Point
YOU
ARE
MOV ING
© Kip Smith, 2003
Near objects appear
to move in the
opposite direction.
Linear Perspective
© Kip Smith, 2003
Perceptual Constancy
© Kip Smith, 2003
Perceptual Constancy
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Definition: perceiving an object as
unchanged although the stimuli we
receive has changed
Two main categories:
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Size Constancy
Brightness/Color Constancy
© Kip Smith, 2003
Size Constancy
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How does it work?
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Visual system computes depth and adjusts
perceived size accordingly
Experiments manipulating depth cues
demonstrate that more depth cues generally
yields more size constancy
© Kip Smith, 2003
Questions?
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You will be responsible for all the material
in this lecture and in Chapters 7 & 8
We have not covered it all in class
If you have questions about anything in
the chapters, ASK!
© Kip Smith, 2003