Sensation and Perception (187-256)
How many senses do humans have?
Vision, Hearing, Taste, Smell and Touch…
Is that it?
There are different levels for each – i.e.
Touch includes pressure, warmth, cold and
pain
Sensation – Process of receiving
information from the environment
Perception – Process of organizing sensory
data and making it meaningful
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Sensation
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Absolute Threshold – The weakest amount
of a stimulus needed in order to be sensed –
the minimum intensity of a given stimulus
that is detectable 50% of the time
 Ex. Hearing Test – No sound, then a faint
beep – 1st beep = Absolute Threshold
 Although they vary from person to person,
values have been determined for each of the
five major senses.
Absolute Threshold Values
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Vision – A candle flame viewed from a
distance of about 30 miles away on a dark
night
Hearing – Ticking of a watch from about 20
feet away in a quiet room
Smell – One drop of perfume diffused
throughout a small house
Taste – One teaspoon of sugar dissolved in
a gallon of water
Touch – Wing of a fly falling on a cheek
from a distance of about 0.4 inch
http://www.bbc.co.uk/science/humanbody/body/interactives/senseschallenge/
Subliminal Messages
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Stimuli that are below the absolute threshold
Difference Threshold
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The Difference Threshold or Just Noticeable
Difference (JND) is the smallest amount of a
change needed in a stimulus before we detect a
change
Ex. Toothpick on the skin
Ex. Books piled in your hands
Weber’s Law
 The
amount of change needed to produce
a JND is a constant proportion of the
original stimulus intensity
 Ex. Adding weights to the bench press
Signal Detection Theory
SDT provides a method for studying sensory
processes while accounting for elements
such as the setting, your physical state,
attitude and moods
 City noises versus suburban noises
 A soldier in wartime vs. peacetime
 Sensory Adaptation
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Transduction
Receptor cells work to transduce
environmental energy into neural impulses
 Ex. Electromagnetic energy is transduced
into electrochemical impulses
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Vision
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Vision is the most dominant of the human
senses – we tend to believe what we see first,
and only secondarily do we accept information
from taste, smell, hearing or touch
Ex. Colored Ketchup and Bagels on St. Patty’s
Day
Light – Electromagnetic Energy
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Not all light is visible to humans
Although other organisms can see different
portions of the electromagnetic spectrum, ROY G
BIV is the only portion visible to humans
ROY G BIV is listed, in order, from the longest to
the shortest wavelength
Physical Characteristics of Light

Wavelength – The distance from one peak to
the next – wavelength determines the Hue,
or color that we experience
 Intensity – The amount of energy in light
waves determined by the height or amplitude
of the wave. Determines the brightness that
we experience
The Eye
When you take a picture with a camera,
light enters through an opening and is
focused on a sensitive surface – “the film”
 Chemicals on the film are changed by the
light and create a lasting impression of the
image that entered the camera
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http://www.youtube.com/watch?v=JadaWSDxBYk&safety_mode=true&persist_s
afety_mode=1
Parts of the Eye
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Cornea – A clear outer covering, behind which
is a fluid.
Iris – Colored, circular muscle that opens and
closes into larger or smaller circles in order to
control the amount of light getting into the eye
Lens – Similar to the lens on a camera – Helps
you to focus the objects that you see onto the
back of the eye to the photoreceptors
Parts of the Eye
Pupil – The opening that changes size as
the iris adjusts to cover or uncover the lens.
Also affected by psychological factors, but
not foolproof
 Retina – The back of the eye which
contains millions of photoreceptors – like
the film of a camera
 Optic Nerve – The bundle of nerves that
carry neural impulses from the eye to the
brain
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Parts of the Eye
 Blind
Spot – The point at which the
optic nerve exits the eye – It is “blind”
because there are no photoreceptors
in this location
 Blind spot demo – Draw two dots
 Fovea – The central focal point in
the retina around which the cones
cluster
Photoreceptors on the Retina
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Rods – Very sensitive to the violet range of
wavelengths – we only see black and white with
them because they contain no color chemicals.
Used for night vision because they respond very
well to low levels of light – rods turn on when it
gets dark
Cones – Used for daylight vision and respond best
to red wavelengths – shut off at night
Mnemonic Devices – A-Rod-Yanks uniforms, Ice
Cream Cone and Road Cones
http://www.nei.nih.gov/health/eyediagram/
Color Vision
A person with normal color vision can
distinguish between almost 7 million
different color shades
 Roughly 1 out of every 50 people are
colorblind (Color-deficient)
 Color blind people are unable to see color
either as the result of an absence of, or a
malfunction of the cones – dichromatic
instead of trichromatic
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http://www.youtube.com/watch?v=CWyrp3hu4KE&safety_mode=true&persi
st_safety_mode=1
Theories of Color Vision
 Young-Helmholtz
Tri-chromatic
Theory – Normal human vision
depends on three different kinds of
cones on the retina – all of the colors
that we see are Red, blue, green, or a
mixture of these
Theories of Color Vision
Hering’s Opponent-Process Theory –
Normal human vision is the result of
opposing retinal processes – Red/Green,
Yellow/Blue and White/Black.
 When incoming visual information is
relayed to the thalamus, some neurons are
“turned on”, while others are “turned off”.
 Helps to explain afterimages
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Afterimages
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Afterimages occur when our neural
response to a given color tires and, as a
result, you see the opposing color when
viewing a white surface
Result of Color Vision
 Color-vision
is a two-part process:
 Red, green and blue cones of the
retina respond to different color
stimuli
 The nervous system then processes the
opponent cells as the information
passes to the visual cortex
Hearing (Audition)
Humans hear a wide range of sounds, but
respond best to frequencies that are in the
range of the human voice
 Humans are very sensitive to faint sounds
– survival mechanism…however, not too
sensitive – Ex. “Ants marching”
 Tremendous ability to distinguish between
a variety of sounds – Ex. Voices of people
you know
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How do we hear?
 Sound
waves (air molecules) collide
with one another, much like the
ripples in a pond after a splash
 Our ears detect changes in air
pressure and then transduce them
into neural impulses which our
brains decode as sounds that have
meaning to us
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http://www.youtube.com/watch?v=_ovMh2A3P5k&feature=related&safety_mode=true&persist_safety_mode
=1
Physical Properties of Sound Waves
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Wavelength – the shorter the wavelength, the
higher the frequency, or number that can pass
in a given period of time. The shorter the
wavelength, the higher the pitch will be (how
high or low a tone is)
Amplitude – the greater the amplitude or height
of the wave, the louder the sound will be – vice
versa
How is sound measured?
 The
loudness of a sound is measured
in a unit called Decibels, abbreviated
dB.
 Zero decibels is considered the
absolute threshold for hearing – the
ticking of a watch 20 ft. away in a
quiet room
Decibel ratings for familiar
sounds:
140 decibels – Shotgun blast
 120 decibels – Thunder
 90-100 decibels – Subway Train
 60 decibels – Normal
conversation
 20 decibels – Whisper
 0 decibels – Absolute Threshold
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The Ear – Outer,
Middle and Inner
 Outer
Ear – The visible portion is
known as the auricle or pinna
 The pinna channels sound waves
through the auditory canal to the
eardrum – a tight membrane that
vibrates with the sound waves
The Middle Ear
 The
vibrations of the eardrum are
transmitted by the middle ear
through three tiny bones – the
Malleus (Hammer), the Incus
(Anvil) and the Stapes
(Stirrup) - to a snail-shaped
tube in the inner ear called the
Cochlea
The Inner Ear
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The incoming vibrations cause the cochlea’s
membrane to vibrate the fluid in the tube
This motion causes ripples in the basilar
membrane, which is lined with hair cells
The hair cells bend, triggering impulses in
adjacent nerve fibers. These hair cells send
neural messages to the brain
Loudness is determined by the number of
hair cells activated
How is pitch determined?
 Place
Theory – States that we hear
different pitches because sound waves
trigger activity at different places
along the cochlea
 Confirmed by cutting holes into
cochleas of cadavers
 Explains how we sense high pitches
How is pitch determined?
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Frequency Theory – Suggests that the
basilar membrane vibrates with incoming
sound waves
This vibration triggers neural impulses to
the brain at the same rate as the sound
wave
The result is that the brain reads pitch
from the frequency of the neural impulses
Explains how we sense low pitches
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Hearing Test
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http://www.noiseaddicts.com/2009/03/can-you-
hear-this-hearing-test/
Hearing Loss
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Conduction Deafness – Occurs when there is
poor transfer of sounds from the eardrum to the
inner ear –often overcome by a hearing aid
Sensorineural Deafness – Results from damage
to the hair cells or auditory nerve – caused by age
and prolonged exposure to loud noise or music –
hearing aids are often of little help
Stimulation Deafness – Very loud sounds
damage the hair cells in the cochlea
http://www.youtube.com/watch?v=yQ17csWENEo&feature=related&safety_mode=true&persist_safety_
mode=1
http://www.youtube.com/watch?v=FEH28KdxjAY&feature=related&safety_mode=true&persist_safety_
mode=1
Touch
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The sense of “Touch” is actually a mix of at
least four, distinct skin touches – Pressure,
warmth, cold and pain
Pain is the body’s way of telling us that
something has gone wrong and that we need to
change our behavior
Some people are born without the ability to
feel pain while others experience chronic pain
– Ex. “Fire alarm”
http://www.youtube.com/watch?v=1vLsZ_dXFAg&safety_mode=true&persist_safety_mode=1
Gate-Control Theory
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The spinal cord contains a neurological
“gate” that either blocks pain signals or
allows them to pass through
Spinal cord contains both small and large
nerve fibers – the small fibers “open” the
gate while the large ones “close” it
Pain can be lessened by stimulating “gateclosing” activity – Ex. Massage,
acupuncture
http://www.youtube.com/watch?v=F656dufb3EQ&safety_mode=true&persist_safety_mode=1
Pain and the Brain
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“Pain is increased by attending to it” – Darwin
Pain is a property of both the senses and the
brain
Phantom Limb Pain – The brain believes
that it will be getting an incoming sensory
message, so the body prepares for it despite
the fact that there may be no limb present
http://www.youtube.com/watch?v=hlQZmNlPdHQ&safety_mode=true&persist_safety_mode=1
http://www.youtube.com/watch?v=YL_6OMPywnQ&safety_mode=true&persist_safety_mode=1
Distracting your brain from a painful
stimulus can help to lessen the sensation –
Ex. Dental Spa
Taste
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Our sense of taste involves four basic sensations –
Sweet, Sour, Bitter and Salty – All other tastes are
mixtures
Taste is a chemical sense – The little bumps on
the top and sides of the tongue are called papillae
Inside the papillae are more than 200 taste buds,
each containing a pore that “catches” food
chemicals
These molecules are then sensed by roughly 50 taste
receptor cells that project hairs onto the pores
http://www.youtube.com/watch?v=N42c52lCQNc&safety_mode=true&persist_safety_mode=1
Different tastes are picked up
by different parts of the tongue:
– Front tip
 Sour – Middle sides
 Bitter – Middle rear
 Salty – Front sides and back sides
 Taste buds are essential to taste, but
smell also plays an important role
 Sweet
Smell (Olfaction)
 Smell
is a chemical sense
 Airborne molecules travel up the
nostrils to receptors located at the top
of the nose
 Receptor cells then send messages to the
olfactory bulb of the brain
 Messages then travel to the temporal
lobe and the limbic system
Olfaction “Tidbits”
 Nursing
infants and mothers have a
heightened sensitivity to scents
 Cologne and perfume instantly
remind us of people
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Ex. Febreeze
 Emotional
responses to smells are
“hard-wired”
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Ex. Response of an adult and baby to a lemon
Perception
Perception is defined as the process
of understanding and interpreting
sensations
 Our primary means of recognizing
objects is through the perception of
its form
 Gestalt – German for “form” –
Stressed that the whole is different
from the sum of the parts
 Basketball perception demo
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http://www.sharpbrains.com/blog/2006/09/28/attention-and-working-memory/
Gestalt Laws of Perception
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Figure-Ground – Figure – any object
perceived as being highlighted against, or in
contrast to, some kind of “unhighlighted”
ground or surroundings
Ex
.
http://www.youtube.com/watch?v=4LbNKJpodEk&safety_mode=true&persist_safety_mode=1
Closure – If a figure has gaps, we complete
it by “filling them in” to form an object
Connectedness/Continuity – we
perceive smooth, continuous patterns
rather than discontinuous ones
Proximity – Elements that are close
to one another are grouped together
Similarity – If figures are similar
to each other, then we group them
together.
Ex. Marching band vid
Depth Perception
 Seeing
images in 3-D allows us to
estimate their distance from us even
though the images produced on the
retina are only two-dimensional
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Ex. Julian Beever http://www.youtube.com/watch?v=XOSa7vjeEU&feature=related&safety_mode=true&persist_safety_mode=1
 Depth
perception appears to be inborn
 Ex. Visual Cliffs
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http://www.youtube.com/watch?v=eyxMq11xWzM&feature=related&safety_mode=true&pe
rsist_safety_mode=1
Binocular Cues
 Our
eyes are about 2 ½ inches apart –
our retinas receive slightly different
images of the world
Retinal Disparity
 The
difference between the two
images perceived by our eyes – the
greater the disparity, the closer
the object – vice versa
Convergence
The extent to which the eyes turn inward
while looking at an object
 The brain notes the angle of convergence
and computes where you are focusing –
the more inward the strain, the closer the
object – vice versa
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Monocular Cues – Cues for
distance – available to either eye alone
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Linear Perspective – We interpret the
apparent convergence of parallel lines as a clue
to distance
Ex. Railroad Tracks
Relative Size and Closeness to the Horizon
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If we assume that two objects are similar
in size, we perceive the one that casts the
smaller image on the retina to be farther
Texture Gradient
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We perceive a gradual change from a coarse,
distinct texture to a fine, indistinct texture as a
sign of increasing distance
Our visual system automatically reads the
receding surface as distance
Ex.
Interposition
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If one object partially covers another, we
perceive it as closer
Light and Shadow
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Nearby objects reflect more light to our eyes
Given two identical objects, the dimmer one seems
farther away
Shading also produces a sense of depth because we
assume light comes from above
Perceptual Constancy – Allows us to
perceive an object as unchanging while
the stimulus we receive from it changes
Size Constancy – Although objects
closer to our eyes produce larger images
on our retinas, we take into account
distance when estimating size
 Ex. Next Slide
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Shape Constancy
 Although
objects produced
from different angles
produced different images on
the retinas, we know the
shape remains constant
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Ex. Next Slide
Brightness
Constancy
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Even though light may reflect off of a
surface, we still perceive objects as
having the same color
Perceptual Sets
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Our experiences, assumptions and
expectations may give us a perceptual set,
or a mental predisposition that greatly
influences what we perceive – we often see
what we expect to see
Top-Down Processing – Occurs
when you use your background knowledge
to fill in gaps that you perceive
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Aoccdrnig to rscheearch at Cmabrigde
Uinervtisy, it deosn't mttaer in waht oredr the
ltteers in a wrod are, the olny iprmoetnt tihng
is taht the frist and lsat ltteer be at the rghit
pclae. The rset can be a toatl mses and you
can sitll raed it wouthit a porbelm. Tihs is
bcuseae the huamn mnid deos not raed ervey
lteter by istlef, but the wrod as a wlohe.
Bottom-Up
Processing
 Also
called Feature Analysis
 We use only the features of an
object to form our perception –
we work from the ground up
 Ex. Learning to read
Possible Essay Questions
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Possible essay questions for Sensation &
Perception Test
Gymnasts use many sensory cues when they perform on
the balance beam, on the uneven bars, on the rings, and
in floor exercises. Discuss three senses that gymnasts rely
on and why they are important.
Explain the theories (2) that describe how people see
color.
People are usually amazed at the figures and words
marching bands can form. Describe four Gestalt grouping
principles that explain how discrete members can be
perceived as part of a larger figure or word.
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http://www.youtube.com/watch?v=EevMBTQpV4U&safety_mode=true&persist_safety_mode=1
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A few extra illusions – File: Perception Examples