This document provides an overview of key concepts in sensation and perception from a lecture on chapter three. It discusses the six major human senses of vision, hearing, touch, taste, smell, and pain. It then explains the basic principles of sensation, which is the detection of stimuli, and perception, which is the interpretation of sensations. Sensory thresholds, adaptation, and transduction are defined. The structures and processes of vision and hearing are described in more detail.

1. Lecture Slides
Chapter Three
Sensation
and
Perception
By Glenn Meyer
Trinity University

2. Introduction: What Are
Sensation and Perception?
vision
6
major
senses
hearing
touch
taste
smell
pain
Vision has been
studied most
extensively and is
the most important
sense for humans,
followed by
hearing.
The list can be
extended
with balance,
joint senses,
and others.

4. Basic Principles of
Sensation and Perception
Two Overlapping Processes:
Perception: process of integrating, organizing, and
interpreting sensations
Example: The splotches of color are recognized as a
basket of fruit.
Sensation: process of detecting a physical stimulus,
such as light, sound, heat, or pressure.
Example: Your eye’s physical response to splotches of
color

5. Basic Terminology
Sensory receptors
Specialized Sensory cells receptors
unique to
each sense organ that
respond to a particular form
of sensory stimulation.
Sensory adaptation
Decline in sensitivity to a
constant stimulus.
Transduction
Process by which a form of
physical energy is converted
into a coded neural signal
that can be processed by the
nervous system.
Click here
Sensory adaptation
Click here
Transduction
Click here

6. Sensory Thresholds
One of the major problems in
studying the senses is to study
thresholds.
There are two issues:
Absolute threshold: smallest
strength of a stimulus that can
be detected
Example: The softest sound
you can hear, the small
concentration of sugar that
can be tasted in your cup of
coffee
Difference threshold: (just
noticeable difference) smallest
difference that can be detected
Example: How much lighter
in weight can a company
make a chocolate bar
before you notice it
The Just Noticeable
Difference
Weber’s law: for each
sense the size of a just
noticeable difference is a
constant proportion of the
size of the initial stimulus
Example: For weight, you
can detect a 2% change.
So if you can bench press
100 lbs., you will notice that
a 102 lb. barbell is heavier.

7. Subliminal Perception
• Detection of stimuli that are below the threshold of
conscious perception or awareness.
• Doesn’t profoundly influence behavior
• Can influence behavior if the stimulus is relevant to your
goals
Subliminal stimuli used in Hassin & others, 2007 study.

8. Vision—What We See
The Nature of Light
• Light is electromagnetic energy that can be described as
waves and by its wavelength
• Various types of electromagnetic energy differ in wavelength,
which is the distance from one wave peak to another.

9. Vision—What We See
The Nature of Light
• Electromagnetic spectrum varies from…
• Note that as wavelength varies, color perception in humans
varies.
• Wavelength itself is not color – color is an interpretation of
wavelength
• Humans see in the 350 to 700 nanometer range.
Very short
Very long

10. Vision—What We See
The Nature of Light
Other animals can see in
the infrared (pit vipers) and
ultraviolet ranges (bees and
some birds)

11. How We See
The Human Visual System –
The Visual Pathway
Light is focused by the cornea and lens
to project an image on the retina.
Cornea: clear membrane that
covers the front of the eye.
Does most of the focusing of
the image
Pupil and iris:
• Colored part of the eye
(iris) and the hole formed
by the iris (pupil)
• Controls the amount of
light entering the eye
• Aids in controlling the
clarity of the image
(smaller pupils, clearer
image)
Lens:
• Transparent structure
behind the pupil.
• Focuses the image on the
retina.
• Changes shape to focus
on far to near targets
through the processes of
accommodation.
Important parts of the pathway in order
Cornea
Click here
Pupil and iris
Click here
Lens
Click here

12. The Retina
 Thin, light-sensitive
membrane located at
back of eye, contains
sensory receptors for
vision
 Rods and cones:
Sensory receptor cells
that respond to light
 Called photoreceptors
 Exposed to light, rods and
cones undergo chemical
reactions that result in
neural signals.

13. Rods and Cones Cones:
• Most located in the
center of the retina
• Fovea: center of retina
with all cones and best
vision
Cones
Click here
• Responsible for best
acuity
• Responsible for color
vision
• Active at daylight or
photopic light levels
Rods:
• Located in the
Periphery of the eye
• Responsible for night
or scotopic vision
Rods
Click here
• Have relatively poor
acuity
• Take approximately 30
minutes to adapt to
lowest light levels

14. The Blind Spot
• The optic disc where ganglion nerve cells leave the retina
• Contains no photoreceptors
• Brain fills in the blind spot with the surrounding patterns

15. Visual Processing in
the Retina
The Route:
Receptors to Bipolars to Ganglion
Cells through Thalamus (LGN) to
Visual Cortex
Bipolar cells
• Collect information from the rods
Bipolar cells
and cones
• Bipolar cells then funnel the
Click here
collection of raw data to the
ganglion cells.
Ganglion cells
• Combines, analyzes, and
encodes the information from
photoreceptors in its receptive
field
Ganglion cells
• Receptive fields are a particular
Click here
area of the retina that feeds to a
ganglion cell.
• Transmits information to the
brain as axons form optic nerve
• Receptive Fields
Are usually circular in nature.
• A single ganglion cell receives
Receptive fields
information from only one or two
cones
Click here
• Can receive information from a
hundred or more rods.

16. Optic Nerve—1 million
ganglion cell fibers
Click here
• Left and right optic nerves meet at
the optic chiasm.
• Fibers of the left and right optic
nerves split in two.
• Images in the left visual field go to
the right hemisphere, images in the
right visual field go to the left
hemisphere.
• Most of the optic nerve axons project
to the brain structure called the
thalamus.
• Responsible for form, color,
brightness, and depth
• Midbrain: a smaller number of axons
deal with location of objects
Visual Cortex
Click here
• Detects edges, angles, lines,
movement, distance
• Specialized neurons know as
feature detectors
• Features are assembled in later
visual cortical areas and frontal
lobes
From Eye to Brain

18. Color Vision—
The Experience
of Color
• Our visual system interprets differences
in the wavelength of light as color
• Rods are color blind, but the cones
allow us to see different colors
• This difference occurs because we have
only one type of rod but three types of
cones
• ROYGBIV
• Wavelengths of about 400
nanometers are perceived as violet.
• Wavelengths of about 700
nanometers are perceived as red.
• In between are orange, yellow,
green, blue, and indigo.
Hue
property of wavelengths
of light known Hue
as color;
different wavelengths
correspond Click here
to our
subjective experience of
color (hue)
Saturation
property of color that
corresponds Saturation
to the
purity of the light wave
Click here
Brightness
perceived intensity of
a Brightness
color, corresponds
to amplitude of the
light Click wave
here

19. Trichromatic
Theory
vs. Opponent-
Process
Theory
Theories of Color Vision
Two theories were proposed in the 1800s
Modern research indicates both have a grain of truth at different neural levels.

20. • Researchers found that by mixing
only three primary lights (usually
red, green, and blue), they could
create the perceptual experience of
all possible colors
Used in TV and computer displays
• Young and Helmholtz to propose
that we have three different types of
photoreceptors, each most sensitive
to a different range of wavelengths
• Three kinds of cones have been
found in the retina – one sensitive to
long wavelengths, one sensitive to
medium wavelengths and one to
short wavelengths.
• These were thought to be a
receptor set specific to red, green
and blue
• Theory explains the most common
forms of color blindness
• Can’t explain well – afterimages and
the unique color yellow
Trichromatic
Theory
Normal Color Vision
Appearance for someone
who is red/green color blind

21. Opponent-
Process
Theory
• Color vision is the product of
opposing pairs of color receptors
• This generates three systems: red–
green, blue–yellow, and black–white
• When one member of a color pair is
stimulated, the other member is
inhibited
• Explains afterimages and color
blindness

22. Hearing – Audition (the technical term
for hearing)
From Vibration to
Sound
• Sound waves are
produced by the
rhythmic vibration of air
molecules
• Auditory perception
occurs when sound
waves interact with the
structures of the ear

23. Characteristics of Sound
The intensity (or amplitude) of a sound wave, measured
in decibels.
The intensity or amount of energy of a wave —
height of a wave; amplitude of a sound wave
determines a sound’s loudness.
Unit of measurement for loudness.
The rate of vibration, or the number of sound
waves per second – measured in Hertz (Hz)
Relative highness or lowness of a sound,
determined by the frequency of a sound wave.
Distinctive quality of a sound, determined by the
complexity of the sound wave.
Loudness
Click here
Amplitude
Click here
Decibel
Click here
Frequency
Click here
Pitch
Click here
Timbre
Click here

24. Intensity of Various Sounds
Decibels
Softest detectable sound
Soft whisper
Quiet neighborhood
Average conversation
Loud music from a radio
Heavy automobile traffic
Very loud thunder
Jet airplane taking off
Loudest rock band on record
Spacecraft launch from 150 ft.
1
10
100
1000
10,000
100,000
1,000,000
10,000,000
100,000,000
1,000,000,000
0
1
2
3
4
5
6
7
8
9
0
20
40
60
80
100
120
140
160
180
Example
P (in sound-pressure
units) Log P

26. How We Hear
The Path of Sound
Sound waves are:
• Collected in the outer ear
• Amplified in the middle ear
• Transduced in the inner ear
Outer Ear: Collects
sound waves;
consists of pinna,
ear canal, and
eardrum (tympanic
membrane)
Middle Ear:
Amplifies sound
waves; consists of
three small bones
(ossicles): hammer,
anvil, and stirrup
Inner Ear: Where
sound is transduced
into neural impulses;
consists of cochlea
and semicircular
canals

27. Structures of the Inner Ear
• Cochlea: coiled, fluid-filled
inner-ear structure that
contains basilar membrane
and hair cells.
• Basilar membrane:
membrane within cochlea of
ear that contains hair cells.
• Hair cells: hair-like sensory
receptors for sound, which are
embedded in basilar
membrane of cochlea. They
get brittle and damaged as
you age, especially by loud
noises (music, work, hair
dryers, gunfire)
Transduction of Sounds
• The structures of the
ear transform changes
in air pressure (sound
waves) into vibrations of
the basilar membrane
• As the basilar
membrane vibrates it
causes the hairs in the
hair cells to bend
• The bending of the
hairs leads to a change
in the electrical potential
within the cell

28. Frequency of Sound Waves
The frequency of a sound wave is measured as the number
of cycles per second (Hertz).
• Highest frequency we can hear
20,000 Hz
• Highest note on a piano
4,186 Hz
• Highest pitch of human voice
1,000 Hz
100 Hz • Lowest pitch of human voice
27 Hz • Lowest note on a piano

29. Distinguishing Pitch
• Humans can hear 20 to 20,000 Hz
• Frequency theory—basilar membrane
vibrates at the same frequency as the
sound wave
• Place theory—different frequencies
cause larger vibrations at different
locations along the basilar membrane
Both frequency theory and place theory are
involved in explaining our discrimination of pitch.
• Frequency theory helps explain our discrimination
of frequencies lower than 500 hertz.
• Place theory helps explain our discrimination of
higher-pitched sounds. For intermediate
frequencies or midrange pitches, both place and
frequency are involved.

30. The Chemical and Body
Senses
• Olfaction -Technical
name for the sense of
smell
• Gustation - Technical
name for the sense of
taste
• Touch and temperature
• Pain
• Kinesthetic (location of
body)
• Vestibular (balance)

31. How We Smell (Don’t answer that!)
Sensory stimuli for
odor are molecules in
the air.
Molecules encounter
millions of olfactory
receptor cells located
high in the nasal
cavity.
Odor receptor seems
to be specialized to
respond to molecules
of a different chemical
structure.
Olfactory receptor
cells stimulation is
converted into neural
messages
Messages pass along
their axons, bundles
of which make up the
olfactory nerve.
Hundreds of different
odor receptors have
been identified.
Brain identifies an
odor by interpreting
the pattern of
olfactory receptors
that are stimulated.
Olfactory bulb – part
of olPfarcotjoercyt fcroormte xth.ere to
temporal lobe for
conscious
recognition and
limbic system for
emotional responses.
Humans have
12,000,000 receptors
as compared with
hundreds of millions
in other animals.

32. Taste
• Tongue covered with little
bumps and grooves lined
with taste buds
• Each taste bud contains 50
receptors for 5 basic tastes
• Five basic tastes – aid us
in seeking nutrient-rich
food
• Sweet
• Sour
• Salty
• Bitter
• Umami – monosodium
glutamate

34. The Skin and Body Senses
Touch – receptors in skin are sensitive to pressure, warmth,
cold or a combination of these
• Pacinian corpuscle is located beneath the skin.
• When stimulated by pressure, Pacinian corpuscle
converts stimulation into a neural message
Pain - The unpleasant sensation of physical discomfort or
suffering that can occur in varying degrees of intensity.
• Pain receptors are called nociceptors. Nociceptors are
actually small
• Composed of sensory fibers, called free nerve endings, in
the skin, muscles, or internal organs.

35. Fast and Slow Pain Systems
A-delta fibers and C fibers
A-delta fibers
• Myelinated A-delta fibers represent the fast pain
system.
• Pathway – thalamus to somatosensory cortex
• A-delta fibers transmit the sharp, intense, but
short-lived pain of immediate injury.
C fibers
• Smaller, unmyelinated C fibers represent the slow
pain system.
• C fibers transmit longer-lasting throbbing, burning
pain of injury
• Pathway – hypothalamus and thalamus and then
to the limbic system (amygdala)

36. Factors That
Influence Pain
Gates
Sensitization:
Pain pathways become more
responsive
Example: Phantom limb pain—
when a person continues to
experience intense painful
sensations in a limb that has been
amputated
Gate-control theory of
pain—pain is a product
of both physiological
and psychological
factors that cause
spinal gates to open
and relay patterns of
intense stimulation to
the brain; the brain
perceives them as pain

37. Movement, Position, and Balance
Vestibular Sense:
Sense of balance, or equilibrium, by
responding to changes in gravity,
motion, and body position.
• Sources of vestibular sensory
information – semicircular canals
and vestibular sacs, located in
ear
Kinesthetic Sense:
The technical name
for the sense of
location and position
of body parts in
relation to one
another
• Proprioceptors:
sensory receptors,
located in the
muscles and joints,
that provide
information about
body position and
movement

38. Perception
Two Major Processes in
Perceptual Processing
• Bottom-up processing—
emphasizes the importance
of sensory receptors in
detecting the basic features
of a stimulus; moves from
part to whole; also called
data-driven processing
• Top-down processing—
emphasizes importance of
observer’s cognitive
processes in arriving at
meaningful perceptions;
moves from whole to part;
also called conceptually
driven processing
• The use of either can be
influenced by cultural
differences or nuances,
such as found in collectivist
vs. individualistic societies
Process of
integrating,
organizing, and
interpreting
sensory
information into
meaningful
representations.

39. ESP: Can Perception
Occur Without
Sensation?
• ESP, or extrasensory
perception: detection of
information by some means
other than through the
normal processes of
sensation.
• Parapsychology: scientific
investigation of claims of
various paranormal
phenomena. Contrary to
what many people think,
very few psychologists
conduct any kind of
parapsychological research
Ongoing controversy:
Majority of scientifically
oriented psychologist are
very skeptical of reports of
ESP

40. The Perception of
Shape - The Influence
of Gestalt Psychology
Figure–Ground
Relationship
• Gestalt psychologists
Gestalt
psychology,
Founded by
German
psychologist Max
Wertheimer in the
early 1900s
(Wertheimer,
1923).
Emphasized that
we perceive whole
objects or figures
(gestalts) rather
than isolated bits
and pieces of
sensory
information.
The separation of a
scene into figure and
ground is not a
property of the actual
elements of the
also thought an
important part of our
perception was the
organization of a
scene at into which
its figure
(the object of
interest) and its
ground (the
background)
you’re looking.
Rather, your ability to
separate a scene into
figure and ground is
a psychological
accomplishment
• Gestalt psychologist
Edgar Rubin (1921)
observed, “In a
certain sense, the
ground has no
shape.” We notice
the shape of the
figure but not the
shape of the
background, even
when that ground is
used as a well-defined
• Demonstrated in
Figure-Ground
Reversal
frame

41. Gestalt Grouping
Principles
• General principle - law of
Prägnanz, or the law of
simplicity:
• When several perceptual
organizations of an assortment
of visual elements are possible,
the perceptual interpretation
that occurs will be the one that
produces the “best, simplest,
and most stable shape”

42. Gestalt Grouping
Principles Proximity
Click here
Similarity
Click here
Closure
Click here
Good
continuation
Click here
Specific
Principles

43. Depth Perception
and Cues
Types of Cues
Monocular—depth
cues that appear in
the image in either
the left or right eye
Binocular—depth
cues that involve
comparing the left
and right eye
images
• One of our more important
perceptual abilities involves
seeing in three dimensions
• Depth perception is difficult
because we only have access to
two-dimensional images
• How do we see a 3D world using
only the 2D retinal images?
• Cue—stimulus characteristics
that influence our perceptions
• We are able to see in 3D
because the visual system can
use depth cues that appear in
the retinal images

44. Monocular Cues
Overlap, Aerial
perspective, Texture
gradient
Relative size, Linear
perspective, Aerial
perspective
Motion parallax

45. Binocular Cues
Binocular disparity:
• Because our eyes are set a few
inches apart, a slightly different
image of an object is cast on the
retina of each eye.
• These distances are interpreted
as depth.
• 3D movies present you with
slightly different images in each
eye and when fused give you a
powerful sense of depth.
• A stereogram is a picture that
uses the principle of binocular
disparity to create perception of a
3D image
• An early problem with vision can
cause this ability not to develop
correctly if the eyes don’t work
together
Convergence:
the degree to
which muscles
rotate your eyes
to focus on an
object

46. Motion Illusions
Stroboscopic motion
• First studied by Gestalt psychologist Max Wertheimer in the early
1900s, stroboscopic motion creates an illusion of movement with two
carefully timed flashing lights
• When retinal image of an object enlarges, we
• If the time interval and distance between the two flashing lights are just
perceive object as moving toward us.
right, a very compelling illusion of movement is created.
• Perception of the speed of the object’s approach
• Basis of movies, TV and computer displays
is based on our estimate of the object’s rate of
enlargement
Induced motion
• Was first studied by Gestalt
psychologist Karl Duncker in the
1920s
• Duncker (1929) had subjects sit in a
darkened room and look at a
luminous dot that was surrounded by
a larger luminous rectangular frame.
When the frame slowly moved to the
right, the subjects perceived the dot
as moving to the left.
• Some neurons are specialized to detect motion in
one direction but not in opposite direction.
• Other neurons are specialized to detect motion at
one particular speed.

47. Perceptual Constancies Perceptual
constancy:
tendency to
perceive objects,
especially familiar
objects, as constant
and unchanging
despite changes in
sensory input
Example: Size As constancy:
a person
walks perception away from of you an
their
retinal image object decreases as
in
size but you know they
are still maintaining the same size.
the
same size despite
Example: changing You images turn a
on
quarter over retina
in your hand
but it still looks round at
any reasonable angle
Shape constancy:
perception of a
familiar object as
maintaining the
same shape,
regardless of image
produced on the
retina

48. Perceptual Illusions
• Misperception of true characteristics of an object or an
image.
• Perceptual illusions underscore the idea that we
actively construct our perceptual representations of
the world according to psychological principles.
The Müller-Lyer
Illusion
Based on interpreting
the angles of lines as
depth cues. The inward
arrows mean the line is
close and thus smaller
for is retinal image
The Illusory Contour
(Kanizsa Square)
Based on Gestalt
principles of closure
and good continuation
as well as the depth
cue of interposition
The Moon Illusion
Based in part on the
fact that people
perceive objects on the
horizon as farther away
than objects that are
directly overhead in the
sky, leading to
misjudging size
Famous Illusions
Click here Click here Click here

49. The Shephard
Tables Illusion
Impossible Figure:
Escher’s Waterfall Illusory Contours
The Müller-Lyer Illusion The Moon Illusion
Dispelled

50. The Effects of Experience on Perception
The tendency to
perceive objects or
situations from a
particular frame of
reference
Example:
• People in industrialized societies are
far more susceptible to the Müller-
Lyer illusion than are people in some
nonindustrialized societies
• May be due to the carpentered-world
hypothesis that people living
in urban, industrialized
environments have a great deal of
perceptual experience in judging
lines, corners, edges, and other
rectangular, objects

51. Controlling Pain
Strategies:
Biofeedback
Acupuncture
Self-Administered Strategies:
Distraction
• Distraction… By actively focusing Click here
your attention on some nonpainful task, you
can often reduce pain
Imagery
• Creating a vivid mental image can help control pain
Imagery… Click here
Relaxation and meditation
• Relaxation Deep relaxation and meditation… can be a very Click effective here
strategy for deterring pain
sensations
Counterirritation
• Counterirritation… Decreases pain by Click creating here
a strong, competing sensation that’s
mildly stimulating or irritating
Positive self-talk and reappraisal
• Positive Make positive self-talk coping and reappraisal… statements, Click either here
silently or out loud, during a
painful episode or procedure