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Sensation & Perception
Creativity is the ability to see relationships where none exist.
Thomas Disch
And now here is my secret, a very simple secret:
It is only with the heart that one can see rightly;
what is essential is invisible to the eye.
Atoine de Saint-Exupéry
What’s the difference?
Sensation
Detecting stimuli from the body or environment
Perception
Organizing sensations into meaningful patterns
Stimulus
Form of energy that can affect sense organs
Sensation
Psychophysics
Study the relationship between stimuli & our
psychological response to them
Sensory receptors
Detect stimuli & convert energy into neural
impulses
Receptors are designed to serve very specific
functions
The curtains in front of the closed window are blowing in the wind, while those in front of the open window
are hanging straight.
The horizon visible through the left window is higher than that visible through the right one.
The waves visible through the left window cannot be seen through the right one.
The door frame is not square. The top piece extends too far to the left.
The legs on the chair next to the door are not touching the floor.
The cord leading from the electric guitar on the floor runs to the telephone instead of a wall jack.
The wine glass contains red wine, while the wine bottle contains white wine.
The left front leg of the guitarist's chair doesn't touch the floor.
The open window sashes are upside down.
The white candle beneath the mirror is "melting" dark wax.
The calendar in front of the candle shows the date as November 31; but November only contains 30 days.
The wall plug on the wall next to the "floating chair" has a plug with no wire connected to it.
The guitarist's right shoelace is tied just above his toes rather than next to his ankle.
The game board beneath the open window has chessmen lined up on the left side, and checkers on the
right.
The reel to reel tape deck in front of the closed window has a 45 rpm record instead of a reel of tape.
The turntable beneath the closed window contains a reel of tape instead of a 33 rpm record.
The mirrored reflection of the hanging coat shows the initials AG, but they should appear as a "mirror
image".
In addition to an orange and two apples, the fruit bowl on the bottom shelf of the table containing the
wine appears to hold a softball.
The unused coat hook on the wall next to the door is mounted upside down.
The hamburger bun between the wine glass and the wine bottle contains a hotdog.
The doorbell is on the interior door frame rather than outside the room.
Thresholds and Stimulus Change
Thresholds
There is a minimum amount of any given sensation that
has to be present for us to notice it
Absolute threshold
This is the minimum amount of a stimulus that is necessary
for us to notice it 50% of the time
Sensory adaptation
If a stimulus is unchanging, we become desensitized to it
Keeps us focused on changes, not constants
Just Noticeable Difference
Just noticeable difference (JND)
Smallest difference in amount of stimulation
that a specific sense can detect
Weber’s law
The size of the JND is a constant proportion of the
initial stimulus
Sensory adaptation- diminished sensitivity
as a consequence of constant stimulation
Subliminal
Below one’s absolute threshold for
conscience awareness
Back-masking- A hidden message that
can be heard when a song is played
backwards
Nothing more than a feeling- does not
have a strong powerful effect on behavior
Beatles
More
The Eye
Red
Our Visible Spectrum
Orange
Yellow Green
Blue
Indigo
Violet
Hue determines color (It’s all in your head)
Depends on length of the distance from one peak to the
next on the wave
Intensity determines brightness
Depends on amplitude of the wave
Can you say the color not what’s
spelled.
YELLOW
BLUE
ORANGE
BLACK
RED
GREEN
PURPLE
YELLOW
RED
ORANGE
GREEN
BLACK
BLUE
RED
PURPLE
GREEN
BLUE
ORANGE
Parts of the Eye
Cornea
Light is initially focused by this transparent covering
over the eye
Pupil
Light enters the eye through this opening
Iris
Muscle connected to the pupil that changes its size to let
in more or less light
Everyone has a unique iris
Parts of the Eye
Lens
This flexible disk under the cornea focuses light onto the
back of the eye
Retina
Light reflected from the lens is received by this sheet of
tissue at the back of the eye
Contains the receptors that convert light to nerve
impulses (transduction happens here)
How we see color: Cones
Retinal cells that respond to particular
wavelengths of light, allowing us to see
color
Most of our cones are located on the fovea,
which gives us the sharpest resolution of visual
stimuli
3 types of cones, each sensitive to different
light frequencies
How we see in the dark: Rods
Retinal cells that are very sensitive to light but
only register shades of gray (i.e., no color)
Rods are located everywhere in the retina
except in the fovea
Rods allow us to see at night without strong light –
this is why we see less color at night
Optic Nerve
In center of retina (Do it yourself pg. 122)
Rods & Cones
How we see color…
Trichromatic theory
3 types of sensors
Red, blue & green receptors
Copy charts at top of 124
How we see color…
Trichromatic theory
3 types of sensors
Red, blue & green receptors
Opponent-process theory
Receptors respond to pairs of colors
White-black / red-green / yellow-blue
Which is correct?
Both!
Auditory System
If a tree falls in the forest with no one
around, does it still make a sound?
No! Sound is the perception (i.e.,
transduction) of moving air waves
Pitch
Frequency of air waves
Loudness/volume
Amplitude of air waves
Compression and Expansion
Highest Frequency? Loudest? Highest
Amplitude? Highest Pitch?
A.
B.
C.
Auditory System
The Ear
Outer ear
Pinna & external auditory canal
Middle ear
Eardrum (tympanic membrane), hammer, anvil
& stirrup
Inner ear
Oval window, cochlea (basilar membrane inside)
Auditory System - Hearing
The process of hearing
Air waves move the tympanic membrane
(eardrum), which moves the hammer, anvil and
stirrup (these all amplify the air wave and pass it
on)….
…to the basilar membrane in the cochlea
Here, different frequencies are transduced via hair cells
(i.e., the rods and cones of the ear) into nerve impulses
that are sent to the auditory cortex of the brain
The Outer Ear
The Middle Ear
The Inner Ear
Theories on hearing
Two theories on transduction in basilar
membrane (i.e., how we perceive sound)
Frequency Theory
Neural impulses are stimulated more with higher
frequencies of air waves
Place Theory
Different frequencies of air waves activate different places
along the basilar membrane
Copy Table 4.4on pg 129
Skin Senses
Touch
Skin is the body’s largest sensory organ
Millions of skin receptors mix and match to
produce specific perception
Four basic types of sensations
Pressure, warmth, cold, and pain
Skin Senses
Temperature
Two separate sensory systems – one for signaling
warmth and the other for signaling cold
Also have distinct spots on the skin that register
only warmth or cold
If you activate both at the same time, the person
perceives ‘hot’!
Skin Senses
Pain
Pain serves a function – it warns
us of impending danger
Endorphins
Neurotransmitters in the brain that have a painkilling effect
Gate-control theory
Pain impulses can be inhibited by closing of
neural gates in the spinal cord
Body Senses
Kinesthetic sense
Provides info about position of joints, muscles, limbs
Gives us control over body movements
Vestibular sense
Provides info about body’s orientation relative to
gravity and head’s position in space
Helps us maintain balance
Relies on semicircular canals in the inner ear
Olfaction (Smell)
Olfaction
Detects molecules in the air
Lock-and-key
Olfactory receptors (i.e., the locks) are built so that
only molecules (the keys) with particular shapes will fit
in particular receptors
Receptors send neural signals to the brain, passing the
the limbic system (emotions) along the way
This is why odors often trigger emotional memories
Gustation (Taste)
Detects molecules of substances that have
dissolved in saliva
Taste buds
Clusters of hair-like receptor cells
Within each bud is a cluster of 50 to 150 receptor
cells
Four types: sweet, sour, salty & bitter
Super tasters v. non tasters
Gustation (Taste)
The sense of taste combines with the sense
of smell to produce perception of flavor of
food
Research suggests that neural impulses for both
senses converge to some degree in brain area
associated with the perception of flavor
When the sense of smell is blocked, we have a
harder time detecting most flavors
Gestalt Principles of Vision
Figure-ground
We recognize figures (objects) by distinguishing
them from the background
Proximity
Marks that are near one another tend to be
grouped together
Gestalt Principles of Vision
Closure
We tend to fill in gaps
in a figure
Similarity
Marks that look alike
tend to be grouped
together
Gestalt Principles of Vision
Continuity
Marks that tend to fall along a smooth curve
or a straight line tend to be grouped together
Depth Perception
How is it that we perceive a 3-dimensional
world when our eyes only project a 2dimensional image on our retinas??!
Our brain uses different cues to perceive depth
Binocular disparity
Since we use both our eyes to focus on an image, the
angles used by each eye to put the image on the fovea of
our retina is used by the brain to perceive distance
Depth Perception
Monocular cues
Our brain also uses information from the stimulus that
does not involve our use of both eyes
Motion
Specifies distance of an object based on its movement
Motion parallax
Texture gradient
Progressive changes in surface texture that signal distance
Linear perspective
Parallel objects seem to get closer together as they get farther
away
Texture Gradient
Linear Perspective
Perceptual Constancy - Vision
The image of an object on your retina can very in
size, shape, and brightness
But we still continue to perceive the object as stable in
size, shape and brightness
Size constancy
The tendency to view an object as constant in size
despite changes in the size of its image on the retina (as
we move)
Shape constancy
The tendency to see an object as retaining its form
despite changes in orientation
Size
Constancy