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Sensation
and
Perception
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What do you feel?
You probably feel your rear against your seat.
Ok, now take a whiff around the room – different odors
are entering your nose (hopefully something pleasant)
Now listen really closely, what do you hear?
probably the hum from the computer or that guy next to
you breathing heavy
Now try to taste what’s in your mouth.
maybe you can dig out a piece of food from your
breakfast or maybe you have that morning breath flavor
funk going on.
Regardless, at this moment, in some distorted way, you
are using all of your senses.
Sensation
• The process by which our sensory
receptors (sense organs) receive
stimulus from the environment.
• What that means is when your body
(through our senses) takes in
information from everything around us,
we are experiencing sensation.
Perception
• The process of organizing and interpreting
sensory information
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So
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sensation is
taking the stuff from outside of us and
bringing it inside our bodies
and
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perception is
our body trying to understanding and
organizing what we take in.
Sensation
Important Concepts
So how does your brain make sense of the world
and form what you understand as reality?
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Bottom-Up Processing (data driven)
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Our sense of reality starts with our sensations and work up
to the brain
The brain takes the info from the senses and we develop a
sense of reality
Top-Down Processing (experience driven)
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Our sense of reality begins with our prior experiences
The brain takes our prior experiences and new current info
and together we develop a sense of reality
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(the brain compares what you are currently seeing with what you
have experienced before)
Input
(sensation)
Processing
(perception)
Top-Down
Processing
Transmission
To brain
Bottom-Up Change of energy
Processing Into information
Detection via
Receptor cells
(flicker, crackle,
Output
Experience, motivation,
And expectations (fond
Campfire memories,
Expectations of warmth
And friendship
Organization and
Interpretation
Behavior, thoughts
And emotions
(move nearer,
warm hands,
Feel comfortable
Transduction
• The process by which our body
transforms light, sound, touch, etc.
into neural impulses that our brain
can understand
Transduction
Light
Eyes
Transduction
Neural messages
What you
consciously see
Do you feel every sensation going on around you??
Sensory Adaptation
Diminished sensory sensitivity as a result of
constant stimulation.
Ex:
When you first go into a restaurant you probably
notice lots of different food smells. However, the
longer you stay the less you notice them. The
smells don’t disappear – people just become less
sensitive to them.
Can you recall a recent time
when, your attention focused
on one thing, you were
oblivious to something else
(perhaps to pain, to someone’s
approach, or to background
music)?
Selective Attention
• The ability to focus on some bits of
sensory information and ignore others
Helps us screen
out irrelevant
stimuli and focus
on relevant
information
Illusionists hope
you have very bad
selective attention
Inattentional Blindness
Failing to see visible objects when we are
focusing our attention elsewhere
An example of selective attention is:
Cocktail Party Effect
The ability to listen to one voice
among many.
Sensory Interaction
One sense may influence another
Ex: Smell may influence taste
Measuring the Senses
• Psychologists assess the accuracy of the
senses in two ways
 Measuring thresholds
 Applying the signal detection theory
Thresholds
Thresholds are the idea that our senses
have basic limits.
• There are two types of thresholds
– Absolute threshold
– Difference threshold (or just noticeable
difference)
Absolute Threshold
The smallest amount of stimulus that a person
can reliably detect
EX: If you can just barely hear a sound – then that is your absolute threshold
for sound
Some common thresholds
Sight = a candle flame seen at 30 miles on a dark
clear night
Hearing = the tick of a watch under quiet conditions
at 20 feet
Taste = 1 teaspoon of sugar in 2 gallons of water
Smell = 1 drop of perfume diffused in a small house
Touch = the wing of a bee falling on your cheek
from a distance of 1 cm
Difference Threshold
• The smallest amount of change needed in
a stimulus before we notice the change
Also known as Just Noticeable Difference
Can you tell the difference??
Weber’s Law
• Used to measure the difference threshold
• The idea that, to perceive a difference between two
stimuli, the change must be proportional to the original
intensity of the stimulus
– The more intense the stimulus, the more it will need to
change before we notice the difference.
Let's say you are holding a 15 lb
bowling ball. If I placed a piece of
paper on that bowling ball, would
you be able to tell the difference
in weight? Most likely if you were
not looking at the situation, you
would not be able to tell the
difference. I would need to add
something heavier relative to the
bowling ball so that you can feel
the difference.
Signal Detection Theory
• This theory examines how outside influences
effect our sensing of stimuli
• The theory says …
– Absolute thresholds are not really absolute
– Things like motivation or physical state can affect
what we sense.
Signal Detection Theory Cont.
• It is the belief that people respond differently to the
same signal and the same person may detect a
particular signal at one time but not another
For example – if I am really hungry for meat, I am more likely to smell a
hamburger than if I was not
– If I think I smell a hamburger, but it is not really there, that is
called a false positive (perceiving stimuli that is not there)
– If a hamburger is grilling right in front of me but I fail to smell
it, that is called a false negative (not perceiving a stimulus
that is present)
Which one is worse??
Subliminal Stimulation
• Below one’s absolute
threshold or conscious
awareness.
Does this work?
Sensations
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We will be covering the following senses
 Vision
 Hearing
 Touch
 Taste
 Smell
 Body
Position and Movement
http://
universe-review.ca/I10-13-senses.jpg
Sense
Hearing
Vision
Touch
Pain
Taste
Smell
What Gets
Stimulated
What Stimulates Us
Sound Waves
Pressure-sensitive hair cells in
cochlea of inner ear
Light Waves
Light-sensitive rods and
cones in retina of eye
Pressure on Skin
Potentially harmful stimuli
Sensitive ends of touch
neurons in skin
Sensitive ends of pain neurons
in skin and other tissue
Molecules dissolved in fluid
Taste cells in taste buds on
the tongue
Molecules dissolved in fluid
Sensitive ends of olfactory
neurons in the mucous
membranes
Touch
Touch (Somatosensation)
• Touch receptors are on the skin
• Four basic skin senses are
– Pain, warmth, cold,
and pressure
Ex: All skin sensations are a
combination of these four basic senses
Burning = warmth + cold + pain
Why do we feel Pain?
Gate-control Theory of Pain
• Pain messages travel on one set of nerve
fibers containing pain gates.
• The gates are open when pain is felt.
• Other sensory messages go through
another set of fibers.
• The non-pain fibers can close the pain
gates to stop the sense of pain.
Vision
Vision
• Photoreceptors in our eyes gather light
• Convert its physical energy into neural
messages
• And send it to the occipital lobe in the brain
for decoding and analyzing
Cornea
• The clear bulge on the front of the
eyeball
• Begins to focus the light by bending it
toward a central focal point
• Protects the eye
Parts of the Eye – Cornea
Iris
• A ring of muscle tissue that forms the
colored portion of the eye
• Regulates the size of the pupil by
changing its size--allowing more or less
light to enter the eye
Parts of the Eye - Iris
Pupil
• The adjustable opening in the center of
the eye that controls the amount of light
entering the eye (surrounded by the iris)
Ex: In bright conditions the iris expands, making the
pupil smaller.
Ex: In dark conditions the iris contracts, making the
pupil larger.
Parts of the Eye - Pupil
Lens
• A transparent structure behind the pupil;
focuses the image on the back of the eye
(retina)
Ex: Glasses or contacts correct problems in the lens’
ability to focus.
Parts of the Eye - Lens
Retina
• Light-sensitive surface with cells that
convert light energy to nerve impulses
• At the back of the eyeball
Made up of three layers of cells
– Receptor cells
– Bipolar cells
– Ganglion cells
Parts of the Eye - Retina
Parts of the Retina:
Receptor Cells
• In sight they change light into neural
impulses the brain can understand.
• Visual system has two types of receptor
cells – rods and cones
Types of Receptor Cells:
Rods:
Can only detect black and white
Need little light to work
Cones:
Can detect sharp images and color
Need a lot of light to work
Clustered in Fovea
Rods and Cones
Parts of Retina
Bipolar Cells
• Gather information
from the rods and
cones and pass it on
to the ganglion cells
• Cells that form the
middle layer in the
retina
Ganglion Cells
•Pass the information
from the bipolar cells
through their axons
•Together these cells
form the optic nerve.
•The top layer of the
cells in the retina
Fovea
• The central focal point of the retina
• The spot where vision is best (most detailed)
Optic Nerve
• The nerve that carries visual information
from the eye to the occipital lobes of the
brain
Types of
Vision
Blind Spot
• The point at which the optic nerve
travels through the retina to exit the eye
• There are no rods and cones at this
point, so there is a small blind spot in
vision.
Why Two Eyes?
• Produces binocular disparity
–Constructing three dimensional
world out of two dimensional retinal
images
Transduction
Conversion of one form of energy to
another.
Light
Eyes
Transduction
For example:
Light energy to vision.
Chemical energy to smell and taste.
Sound waves to sound.
Neural messages
What you
consciously see
Hue
• The color of light as determined by the
wavelength of the light energy
• Includes: red, orange, yellow, green,
blue, indigo and violet (ROY G BIV)
• The eye can detect 7 million separate
hues
Amplitude
• The brightness of
light as determined
by height of the
wave
• The taller the wave,
the brighter the color
What makes up a light wave?
Wavelength
• The distance from the peak of
one light wave to the peak of the
next.
•The distance determines the hue
(color) of the light we perceive.
Intensity
The amount of energy in a light wave.
Determined by the height of the wave.
The higher the wave the more intense
the light is. (brightness)
How do we see in color?
What color is this dragon?
Color
• The dragon is anything but red.
• The dragon rejects the long
wavelengths of light that to us are
red- so red is reflected of and we see
it.
• Also, light has no real color.
• It is just energy turned into color by
our eyes
• It is our mind that perceives the color.
What enables you to
perceive color??
Two major color theories!
Young-Helmholtz Trichromatic
(three color) Theory
•3 different types of photoreceptor cells in our
eyes.
• Realized that any color can be created by combining
the light waves of three primary colors
Ex: Most colorblind people simply lack cone receptor cells for one or more of these primary colors.
– Not really blind – just limited in what colors they can see
Click here to simulate color blindness
Opponent-Process Theory
• The visual system has receptors that react in opposite
ways to three pairs of colors (red-green, blue-yellow,
and white-black).
– These are antagonist/ opponent colors.
– Light that stimulates one half of the pair inhibits the
other half
– Produces afterimages
Afterimages – colors perceived after
other, complementary colors are
removed
Afterimage Effect
Sensory Disorder
• Synesthesia
• Anosmia
• The boy who sees without eyes