This document provides an overview of key concepts in sensation and perception, as presented in a PowerPoint by Jim Foley. It discusses the senses and how sensory information is processed by the brain to form perceptions. Specific topics covered include the distinction between sensation and perception, thresholds, sensory adaptation, perceptual set, effects of context and emotion on perception, vision and color perception, visual processing in the brain, and how perceptual organization allows us to interpret sensory input.

1. Sensation
and
Perception
PowerPoint®
Presentation
by Jim Foley
Chapter 6

2. What we’ll sense and perceive…
in this chapter:
 Sense:
 especially vision and hearing
 smell, taste, touch, pain, and
awareness of body position
 How do the sense organs and
nervous system handle incoming
sensory information?
 How does the brain turn sensory
information into perceptions?
 Why is our style of creating
perceptions better at perceiving
the real world than at decoding
tricky optical illusions?

3. Basic Principles of
Sensation and
Perception
Your brain will interpret, perceive
these topics as they enter your
sense organs:
 Sensation vs. Perception, Bottom-
Up vs. Top-Down Processing
 Transduction and Thresholds
 Sensory Adaptation
 Perceptual Set
 Context Effects on perception
 Emotion/Motivation effects

4. Sensation vs. Perception
“The process by which our
sensory receptors and
nervous system receive and
represent stimulus energies
from our environment.”
“The process of organizing
and interpreting sensory
information, enabling us
to recognize meaningful
objects and events.”
The brain
receives input
from the
sensory organs.
The brain makes
sense out of the
input from
sensory organs.
Sensation Perception

5. Making sense of the world
What am I
seeing?
Is that
something I’ve
seen before?
Bottom-up
processing:
taking sensory
information and
then assembling
and integrating it
Top-down
processing:
using
models, ideas, and
expectations to
interpret sensory
information

6. Do you see a
painting or a 3D
bottle?
What’s on the
bottle?
Kids see eight to
ten dolphins.
Why do you think
kids see
something
different than
adults?

7. Top-down
Processing
You may start
to see
something in
this picture if
we give your
brain some
concepts to
apply:
“tree”
“sidewalk”
“dog”
“Dalmatian”

8. From Sensory Organs to the Brain
The process of sensation can
be seen as three steps:
Reception--
the stimulation
of sensory
receptor cells by
energy
(sound, light, he
at, etc)
Transduction--
transforming
this cell
stimulation into
neural impulses
Transmission--
delivering this
neural
information to
the brain to be
processed

9. Thresholds
The absolute threshold: the
minimum level of stimulus
intensity needed to detect a
stimulus half the time.
Anything below this
threshold is considered
“subliminal.”

10. When Absolute Thresholds
are not Absolute
10
Signal detection theory
refers to whether or not we
detect a stimulus, especially
amidst background noise.
This depends not just on
intensity of the stimulus but
on psychological factors
such as the person’s
experience, expectations, m
otivations, and alertness.

11. Subliminal Detection
 Although we cannot learn complex
knowledge from subliminal
stimuli, we can be primed, and this
will affect our subsequent choices.
 We may look longer at the side of
the paper which had just showed a
nude image for an instant.
Subliminal:
below our threshold for
being able to consciously
detect a stimulus

12.  Difference threshold: the minimum difference (in
color, pitch, weight, temperature, etc) for a person to
be able to detect the difference half the time.
 Weber’s law refers to the principle that for two
stimuli to be perceived as different, they must differ
by a minimum percentage:
 2 percent of weight
 8 percent of light intensity
 0.3 percent of sound wave frequency to notice a
difference in pitch.
 Any changes noticeable on this slide?
The “Just Noticeable Difference”

13.  To help detect novelty in our
surroundings, our senses
tune out a constant stimulus,
such as:
 a rock in your shoe
 the ticking of a clock
 If you concentrate on
keeping your eyes in one
spot, you’ll see the effects,
as your eyes adjust to stimuli
 Visual sensory adaptation
will be tested when
discussing opponent-process
theory.
Sensory Adaptation

14. Perceptual Set
Perceptual set is what we expect to see, which influences
what we do see.
Perceptual set is an example of top-down processing .
Loch Ness monster
or a tree branch?
Flying saucers
or clouds?

15. Perceptual set can be “primed.”
Old
woman
Young
woman
Ambig
uous

16. Context Effect on Perception
Spelling test answers:
In which picture does the center dot look larger?
Perception of size depends on context.
Did context affect which word you wrote?
apple payor payee pairdouble pear

17. Effect of Emotion, Physical State, and
Motivation on Perception
Experiments show that:
 destinations seem farther
when you’re tired.
 a target looks farther
when your crossbow is
heavier.
 a hill looks steeper with a
heavy backpack, or after
sad music, or when
walking alone.
 something you desire
looks closer.

18. Vision, and Perceptual Organization
and Interpretation
And: ESP, Perception without Sensation
Vision (Sensation):
 The Eye
 From light input to mental
images
 Retina and Receptors
 Feature Detection
 Parallel Processing
 Color Vision
Visual Organization:
 Form, Depth, and Motion
Perception
 Size, Shape, and Color
Constancy
 Visual Interpretation:
 Restored Vision
 Perceptual Adaptation
Topics we’ll be looking into:

19. The
Visible
Spectrum
We encounter waves
of electromagnetic
radiation.
Our eyes respond to
some of these waves.
Our brain turns these
energy wave
sensations into colors.
Vision:
Energy, Sensation, a
nd Perception

20. Color/Hue and
Brightness
We perceive the
wavelength/frequency of
the electromagnetic
waves as color, or hue.
We perceive the
height/amplitude of
these waves as
intensity, or
brightness.

21.  Light from the candle passes through the cornea and the
pupil, and gets focused and inverted by the lens. The
light then lands on the retina, where it begins the
process of transduction into neural impulses to be sent
out through the optic nerve.
 The lens is not rigid; it can perform accommodation by
changing shape to focus on near or far objects.
The Eye

22. The Retina

23. The Blind
Spot
 There is an area of missing information
in our field of vision known as the blind
spot. This occurs because the eye has no
receptor cells at the place where the
optic nerve leaves the eye.
 To test this, walk slowly up to the screen
with one eye closed and the other eye
fixed on the dot, and one of the phones
will disappear.

24. Photoreceptors: Rods and Cones
 When light reaches the back of the retina, it triggers
chemical changes in two types of receptor cells:
 Rods help us see the black and white actions in our
peripheral view and in the dark.
 Cones help us see sharp colorful details in bright light.

25. Visual Information Processing
The images we
“see” are not
made of light;
they are made of
neural signals
which can be
produced even
by pressure on
the eyeball.
The rods and cones send messages to ganglion and
bipolar cells and on to the optic nerve.
Once neural signals enter the optic nerve, they are sent
through the thalamus to the visual cortex.

26. Turning Neural Signals into Images
 In the visual cortex are neurons called feature
detectors: they respond to certain visual aspects of
the environment.
 These cells in turn send information to neural
networks (supercell clusters) that can perform tasks
such as recognizing individual faces.
Faces
Houses
Chairs
Houses and Chairs
Feature detection areas

27. Parallel Processing
 Turning light into the mental act of seeing:
light waveschemical reactionsneural impulsesfeaturesobjects
and one more step...
 Parallel processing: building perceptions out of sensory
details processed simultaneously in different areas of the
brain. For example, a flying bird is processed as:

28. Visual Processing

29. Color Vision
Young-Helmholtz Trichromatic
(Three-Color) Theory
According to this theory, there are
three types of color receptor
cones--red, green, and blue. All the
colors we perceive are created by
light waves stimulating
combinations of these cones.

30. Color Blindness
People missing red cones or green
cones have trouble differentiating red
from green, and thus have trouble
reading the numbers to the right.
Opponent-process theory refers to
the neural process of perceiving white
as the opposite of perceiving black;
similarly, yellow vs. blue, and red vs.
green are opponent processes.

31. Opponent-Process Theory Test
The dot, the dot, keep staring at the dot in the center…

32. Turning light waves into mental images/movies...
Visual Perceptual Organization
We have perceptual processes for enabling us to
organize perceived colors and lines into objects:
 grouping incomplete parts into gestalt wholes
 seeing figures standing out against background
 perceiving form and depth
 keeping a sense of shape, size, and color constancy
despite changes in visual information
 using experience to guide visual interpretation
 Restored vision and sensory restriction
 Perceptual adaptation

33. The Role of
Perception
Our senses take in the blue
information on the right.
However, our perceptual
processes turn this into:
1. a white paper with blue
circle dots, with a cube
floating in front.
2. a white paper with blue
circle holes, through
which you can see a
cube.
3. a cube sticking out to
the top left, or bottom
right.
4. blue dots (what cube?)
with angled lines inside.

34. Figure-Ground Perception
 In most visual scenes, we pick out objects and figures,
standing out against a background.
 Some art muddles this ability by giving us two equal
choices about what is figure and what is “ground”:
Stepping
man, or
Goblet or two
faces?

35. Grouping: How We Make Gestalts
“Gestalt” refers to a meaningful
pattern/configuration, forming a “whole” that is more than
the sum of its parts.
Three of the ways we group visual information into
“wholes” are proximity, continuity, and closure.

36. Grouping Principles
Which ones influence perception here?

37. Visual Cliff: A Test of Depth Perception
Babies seem to develop this ability at crawling age.
Even newborn animals fear the perceived cliff.

38. Perceiving Depth: Binocular Methods
Unlike other animals, humans have
two eyes in the front of our head.
This gives us retinal disparity; the
two eyes have slightly different
views. The more different the views
are, the closer the object must be.
This is used in 3D movies to create
the illusion of depth, as each eye
gets a different view of “close”
objects.
How do we perceive depth
from a 2D image?...
by using monocular (needing
only one eye) cues

39. Monocular Cue: Interposition
Interposition:
When one object appears
to block the view of
another, we assume that
the blocking object is in a
position between our eyes
and the blocked object.

40. Monocular Cue:
Relative Size
We intuitively know to
interpret familiar objects (of
known size) as farther away
when they appear smaller.

41. Monocular Cues:
Linear Perspective and Interposition
The flowers in the
distance seem
farther away
because the rows
converge. Our
brain reads this as
a sign of distance.

42. Tricks Using
Linear
Perspective
 These two
red lines
meet the
retina as
being the
same size
 However, our
perception of
distance
affects our
perception of
length.

43. Monocular Cue: Relative Height
 We tend to perceive
the higher part of a
scene as farther away.
 This scene can look like
layers of
buildings, with the
highest part of the
picture as the sky.
 If we flip the
picture, then the black
part can seem like
night sky… because it is
now highest in the
picture.

44. Monocular Cues: Shading Effects
Shading helps our
perception of
depth.
Does the middle
circle bulge out or
curve inward?
How about now?

45. Light and shadow create depth cues.

46. Monocular Cues: Relative Motion
When we are
moving, we can tell
which objects are
farther away because it
takes longer to pass
them.
A picture of a moon on
a sign would zip behind
us, but the actual moon
is too far for us to pass.

47. Perceptual Constancy
Our ability to see objects as appearing the same
even under different lighting conditions, at
different distances and angles, is called
perceptual constancy. Perceptual constancy is a
top-down process.
Examples:
 color and brightness constancy
 shape and size constancy

48. Color Constancy
 This ability to see a
consistent color in changing
illumination helps us see
the three sides as all being
yellow, because our brain
compensates for shading.
 As a result, we interpret
three same-color blue
dots, with shades that are
not adjusted for shading, as
being of three different
colors.

49. Brightness Constancy
On this screen, squares A
and B are exactly the
same shade of gray.
You can see this when
you connect them.
So why does B look
lighter?

50. Shape Constancy
Shape constancy refers to the ability to perceive objects
as having a constant shape despite receiving different
sensory images. This helps us see the door as a
rectangle as it opens. Because of this, we may think the
red shapes on screen are also rectangles.

51. Size Constancy
 We have an ability to use distance-related context
cues to help us see objects as the same size even if
the image on the retina becomes smaller.
 The Ames room was invented by American
ophthalmologist Adelbert Ames, Jr. in 1934.
 The Ames room was designed to manipulate distance
cues to make two same-sized girls appear very
different in size.

52. Visual Interpretation: Restored vision, sensory restriction
Experience shapes our visual perception
 People have grown up without vision
but then have surgically gained sight
in adulthood. They learned to
interpret depth, motion, and figure-
ground distinctions, but could not
differentiate shapes or even faces.
 Animals raised at an early age with
restrictions, e.g. without seeing
horizontal lines, later seem unable to
learn to perceive such lines.
 We must practice our perception skills
during a critical period of
development, or these skills may not
develop.
Being blind between
ages 3 and 46 cost
Mike his ability to
learn individual faces.

53. Perceptual Adaptation
 After our sensory
information is
distorted, such as by a
new pair of glasses or by
delayed audio on a
television, humans may
at first be disoriented but
can learn to adjust and
function.
 This man could learn
eventually to fly an
airplane wearing these
unusual goggles, but
here, at first, he is
disoriented by having his
world turned upside
down.

54. The Nonvisual Senses
There’s more to Sensation and
Perception than meets the eye
 Hearing: From sound to ear to
perceiving pitch and locating sounds.
 Touch and Pain sensation and
perception
 Taste and Smell
 Perception of Body Position and
Movement

55. Hearing  How do we take a
sensation based on sound
waves and turn it into
perceptions of
music, people, and
actions?
 How do we distinguish
among thousands of
pitches and voices?

56. Hearing/Audition: Starting with Sound
Height or
intensity of
sound wave;
perceived as
loud and soft
(volume)
Perceived as
sound quality
or resonance
Length of the
sound wave;
perceived as
high and low
sounds
(pitch)

57. Sound Waves Reach The Ear
The outer ear
collects sound
and funnels it
to the eardrum.
In the middle ear, the sound waves hit
the eardrum and move the
hammer, anvil, and stirrup in ways that
amplify the vibrations. The stirrup
then sends these vibrations to the oval
window of the cochlea.
In the inner
ear, waves of fluid
move from the
oval window over
the cochlea’s
“hair” receptor
cells. These cells
send signals
through the
auditory nerves to
the temporal lobe
of the brain.

58. The Middle and Inner Ear
Conduction Hearing Loss:
when the middle ear isn’t
conducting sound well to the
cochlea
Sensorineural Hearing Loss:
when the receptor cells aren’t
sending messages through the
auditory nerves

59. Preventing
Hearing Loss
 Exposure to sounds that
are too loud to talk over
can cause damage to
the inner ear, especially
the hair cells.
 Structures of the middle
and inner ear can also
be damaged by disease.
 Prevention methods
include limiting
exposure to noises over
85 decibels and treating
ear infections.

60. Treating Hearing Loss
 People with conduction
hearing loss may be helped
by hearing aids. These aids
amplify sounds striking the
eardrum, ideally amplifying
only softer sounds or
higher frequencies.
 People with sensorineural
hearing loss can benefit
from a cochlear implant.
The implant does the work
of the hair cells in
translating sound waves
into electrical signals to be
sent to the brain.

61.  Loudness refers to
more intense sound
vibrations. This
causes a greater
number of hair cells
to send signals to
the brain.
 Soft sounds only
activate certain hair
cells; louder sounds
move those hair
cells AND their
neighbors.
Sound Perception: Loudness

62. Sound Perception: Pitch
Frequency theory
At low sound frequencies, hair
cells send signals at whatever
rate the sound is received.
Place theory
At high sound frequencies,
signals are generated at
different locations in the
cochlea, depending on pitch.
The brain reads pitch by
reading the location where the
signals are coming from.
How does the inner ear turn sound
frequency into neural frequency?
Volley Principle
At ultra high
frequencies, receptor cells fire in
succession, combing signals to
reach higher firing rates.

63. Sound Perception: Localization
How do we seem to know the location of the source
of a sound?
 Sounds usually
reach one of our
ears sooner, and
with more
clarity, than they
reach the other
ear.
 The brain uses this
difference to
generate a
perception of the
direction the
sound was coming
from.

64. Other Senses
We may not have all of the
sensory abilities of the shark
(such as sensing the electric
fields of others) or migratory
birds (such as orienting by the
earth’s magnetic field).
But we do have senses of:
 smell and taste.
 four different components of the sense of
touch.
 body/kinesthetic awareness.

65. Touch
Touch is valuable…
 for expressing
and sensing
feelings.
 for sharing
affection, comfort
, and support.
 for detecting the
environment in
multiple
ways, such as
pressure, warmth
, cold, and pain.

66. Four Components
of Touch
 Stroking adjacent
pressure spots
creates a tickle.
 Adjacent cold and
pressure sensations
feel wet.
 Adjacent warm and
cold feels searing hot.
Warmth
PainCold
Pressure

67. Pain...what is it good for?
 Pain tells the body
that something has
gone wrong. Pain
often warns of severe
injury, or even just to
shift positions in a
chair to keep blood
flowing.
 Not being able to feel
pain, as in Ashley’s
case, means not being
able to tell when we
are injured, sick, or
causing damage to
our bodies.

68. Biological Factors in Pain Perception:
The Pain Circuit
Nociceptors are sensory receptors whose
signals are interpreted by the brain as pain.
The pain circuit
refers to signals
that travel to the
spinal cord, up
through small
nerve
fibers, which then
conduct pain
signals to the
brain.

69.  Gate-Control Theory
This theory hypothesizes that the spinal cord contains a
neurological “gate” that blocks pain signals or allows
them to pass on to the brain. Stimulating large nerve
fibers in the spinal cord through
acupuncture, massage, or electrical stimulation seems
to close that gate.
 Endorphins
These hormones can be released by the body to reduce
pain perception.
 Phantom Limb Sensation
As the brain produces false sounds (tinnitus, ear
ringing) and sights (aura, lights with migraines), it can
produce pain or other perception of amputated/missing
arms or legs.
Biological Factors in Pain Perception

70. Psychological Influences on Pain
Distraction, such as
during intense
athletic competition,
can limit the
experience of pain.
Pain and Memory
 Memories of pain
focus on peak
moments more
than duration.
 Tapered pain is
recalled as less
painful than
abruptly-ended
pain.

71. Social and Cultural Influences
on Pain Perception
 Social contagion
We feel more pain if other people are experiencing
pain. This occurs either out of
empathy/mirroring, or a shared belief that an
experience is painful.
 Cultural influences
We may not pay attention as much to pain if we
see a high level of pain endurance as the norm for
our family, peer group, or culture.

72. Controlling/Managing/Reducing Pain
 Pain can be reduced through drugs, acupuncture, electrical
stimulation, exercise, hypnosis, surgery, relaxation
training, and distraction.
 Even the placebo effect has real influence on pain
perception. When we think we are taking pain killers or
receiving acupuncture, our bodies can release endorphins.
 Distraction with virtual reality immersion (below) has
helped burn victims manage intense pain.

73. Biopsychosocial Influences on
Pain Perception
Examples of each
influence:
 gate control
 selective
attention
 empathy pain

74. Sweet:
energy source
Sour:
potentially toxic
acid
Umami:
(savoriness)
proteins to grow
and repair
tissue
Salty: sodium
essential to
physiological
processes
Bitter:
potential
poisons
Taste
Our tongues have
receptors for five different
types of tastes, each of
which may have had
survival functions.

75. Neurochemistry of Taste
 There are no regions of the tongue,
just different types of taste
receptor cells projecting hairs into
each taste bud’s pore.
 These cells are easily triggered to
send messages to the temporal
lobe of the brain.
 Burn your tongue? Receptors
reproduce every week or two. But
with age, taste buds become less
numerous and less sensitive.
 Top-down processes still can
override the neurochemistry;
expectations do influence taste.

76. Smell: Odor Receptors
Humans have a poor sense of smell for an animal. Even
so, humans have 350 different types of smell receptors
allowing us to detect about 10,000 different odors.

77. Smell: The Shortcut Sense
 Sensations of smell take a
shortcut to the
brain, skipping the trip
through the “sensory
switchboard” (thalamus)
made by all the other
senses.
 Information from the nose
goes not only to the
temporal lobe but also to
the limbic
system, influencing
memory and emotion.
 Smell links lovers, parent
and child, and other
creatures to each other

78. Sensing Body Position and Movement
 Kinesthesis (“movement
feeling”): sensing the
movement and position of
individual body parts relative
to each other.
 How it works: sensors in the
joints and muscles send
signals that coordinate with
signals from the
skin, eyes, and ears
 Without kinesthesis, we
would need to watch our
limbs constantly to
coordinate movement.

79. Sensing Body Position and Movement
 Vestibular sense: the ability to sense
the position of the head and body
relative to gravity, including the sense
of balance.
 How it works: fluid-filled chambers in
the inner ear (vestibular sacs and
semicircular canals) have hairlike
receptors that send messages about
the head’s position to the cerebellum
 Vestibular sense serves as the human
gyroscope, helping us to balance and
stay upright.

80. Mixing the different senses together
Sensory interaction occurs
when different senses
influence each other.
For example:
 a burst of sound makes a
dim light source more
visible.
 flavor is an experience not
only of taste, but also of
smell and texture.
 seeing text or lip
movement, or even
feeling the puff of air from
consonants, affects what
words we hear.
456789
Synaesthesia is a condition
when perception in one
sense is triggered by a
sensation in a DIFFERENT
sense.
Some people experience
synaesthesia all the
time, reporting that, “the
number 7 gives me a salty
taste” or “rock music seems
purple.”

81. Embodied Cognition
 holding a warm mug promotes social warmth.
 social rejection looks like pain reception in the brain.
 words on a heavy clipboard seem… weighty.
 being ignored (cold shoulder) makes a room seem
colder.
 leaning left physically  leaning left politically.
 in a foul smelling room, people were more likely to
suspect bad intentions (foul play) by others.
It’s no coincidence that we use sensation words to describe
feelings. Studies seem to show that:
Embodied cognition refers to the effect of
body experience on feelings, attitudes,
thoughts, and judgments.

82. Extrasensory Perception (ESP)
Extrasensory Perception (ESP) can defined, literally, as
perception without sensation.
Believers in ESP think that it involves getting accurate
information directly to the mind, skipping the known
senses.
Types of ESP include:
 telepathy (“reading” messages from other minds).
 clairvoyance (“seeing” remote events).
 precognition (“knowing” the future).
The evidence for ESP is anecdotal and controversial;
people seem to notice times when predictions come true
and perceptions match reality, but tend to disregard the
times when they do not.

83. Summarizing the Senses