Sensation
and
Perception
 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

So sensation is


taking the stuff from outside of us and
bringing it inside our bodies
and 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?

Bottom-Up Processing (data driven)



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)


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

(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
Bottom-Up Processing
• Let’s start off with an important
term – transduction
• The process by which our body
transforms light, sound, touch, etc.
into neural impulses that our brain
can understand
Transduction
Conversion of one form of energy to
another.
Stimulus energies changed to neural impulses.
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.
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
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
• Smell may influence taste
What if we could sense everything?
Life would hurt.
So we can only take in a window of what is
out there.
Psychophysics: the study of the
relationship between physical stimuli and our
psychological experiences to them. – i.e. is
blue really blue??
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
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 (jnd)
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
– What???
– The more intense the stimulus, the more it will need to
change before we notice the difference.
Weight – 10%
Hearing – 5%
Vision – 8%
How do businesses use Weber’s
Law?? - Movie theater example
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?
Yes and No
• A few studies did show some small emotional
reactivity (called priming a response).
• However, the effects are subtle and fleeting.
Sensations

We will be covering the following senses
 Vision
 Hearing
 Touch
 Taste
 Smell
 Body
Position and Movement
http://www.fotosearch.com/comp/IMZ/IMZ166/vmo0128.jpg
Of The 5 Senses, Which Would You
Choose To Lose? Why?
http://
universe-review.ca/I10-13-senses.jpg
Sense
Hearing
Vision
Touch
Pain
What Stimulates Us
What Gets
Stimulated
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
Sensitive ends of touch
neurons in skin
Sensitive ends of pain
Potentially harmful stimuli neurons in skin and other
tissue
Taste cells in taste buds
on the tongue
Taste
Molecules dissolved in fluid
Smell
Sensitive ends of
Molecules dissolved in fluid 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
• All skin sensations are a
combination of these
four basic senses
• Burning = warmth +
cold + pain
Pain
• Why do we experience pain??
– Your body’s way of telling you something has
gone wrong
• Biopsychosocial Perspective on Pain
Biological Influence
• Activity in spinal cord
• Genetic differences in
endorphin production
Social-Cultural Influences
• Presence of others
• Empathy for others’ pain
• Cultural expectations
Psychological Influences
• Attention to pain
• Learning based on experience
• Expectations
Personal
Experience
Of 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 nonpain fibers can close the pain
gates to stop the sense of pain.
Vision
http://www.fofweb.com/Electronic_Images/onfiles/SciHumP
http://webvision.med.utah.e
http://www.cs.umsl.edu/~sanjiv/cs440/mike_project/retina.gif
www.photo
.net
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
That’s basically
it….
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; creates a hole
in the center of the iris (pupil)
• 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)
• In bright conditions the iris expands,
making the pupil smaller.
• 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)
• Muscles that change the thickness of the
lens change how the light is bent
thereby focusing the image
• 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
Receptor Cells
• These cells are present in every sensory
system to change (transduce) some other
form of energy into neural impulses.
• In sight they change light into neural
impulses the brain can understand.
• Visual system has two types of receptor
cells – rods and cones
Rods
• Visual receptor cells located in the
retina
• Can only detect black and white
• Respond to less light than do cones
Cones
• Visual receptor cells located in the
retina
• Can detect sharp images and color
• Need more light than the rods
• Many cones are clustered in the
fovea.
Rods and Cones
Fovea
• The central focal point of the retina
• The spot where vision is best (most detailed)
Types of
Vision
Optic Nerve
• The nerve that carries visual information
from the eye to the occipital lobes of the
brain
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.
Processing
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
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.
Stimulus energies changed to neural impulses.
Light
Eyes
Transduction
Neural messages
How is this important when
studying sensation?
For example:
Light energy to vision.
Chemical energy to smell and taste.
Sound waves to sound.
What you
consciously see
We only use light energy to
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 off 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
•Guessed that we have 3 different types of
photoreceptor cells in our eyes.
•Each with differing sensitivities to different
light wavelengths
• Realized that any color can be created by
combining the light waves of three primary colors
•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