CHAPTER 8: SENSATION
AND PERCEPTION
JOURNAL #1
 Did you do anything AWESOME this weekend?! Explain..
 Of your five senses, which do you find to be most important?
 If you had to lose one, either seeing or hearing, which would
you rather keep and why?
 List the five senses 1 -5, 1 being the most important or
necessary, and 5 being the least important.
8.1
 Objectives
 Describe the field of study known as psychophysics.
 Define and discuss threshold, Weber ’s law, and signal
detection.
8.1
Sensation
• A sensation occurs anytime a stimulus
activates one of your receptors.
• Any aspect of or change in the
environment to which an organism
responds is called a stimulus.
•Ex.- light turn on/ off, alarm clock, hand
touch
• A stimulus can be measured in many
physical ways, including its size, duration,
intensity, or wavelength.
8.1- SENSATION
• A sensation can be
combined with other
sensations and your
past experiences to
yield a perception.
• Psychophysics—the
study of the relationship
between sensory
experiences and the
physical stimuli that
causes them.
FIGURE 1
Fraser’s Spiral
Fraser’s spiral illustrates the
difference between sensation and
perception. Our perception of this
figure is that of a spiral, but it is
actually an illusion. Trace a circle
carefully. Your finger will always come
back to its starting point.
8.1
• Psychologists conduct experiments to
determine the absolute threshold of the
senses.
• Absolute threshold- Weakest amount of a
stimulus required to produce a sensation,
detected 50% of the time
8.1
• The absolute threshold for the five senses
is as follows:
– Vision—seeing a candle flame 30 miles away on
a clear night.
– Hearing—hearing a watch ticking 20 feet away.
– Taste—tasting 1 teaspoon of sugar dissolved in 2
gallons of water.
– Smell—smelling 1 drop of perfume in a 3-room
house.
– Touch—feeling a bee’s wing falling a distance of
1 centimeter onto your cheek.
8.1
The Human Senses
This chart lists the fundamental features that make up the human sensory system.
8.1
• The difference threshold is the smallest
change in a physical stimulus that can be
detected between two stimuli half the time.
•Ex.- shine two lights and detect which is
brighter
• The just noticeable difference (JND) refers
to the smallest increase or decrease in the
intensity of a stimulus that a person is able
to detect half the time.
8.1
• A particular sensory experience depends
more on the changes in the stimulus than
on the absolute size or amount.
• Weber’s law: the larger or stronger a
stimulus, the larger the change required
for a person to notice that anything has
happened to it.
•Ex.- backpack full of oranges
8.1
• Our senses have an ability to adapt, or
adjust themselves, to a constant level of
stimulation  sensory adaptation
• They get used to a new level and respond
only to deviations from it.
ON THE BACK OF YOUR LAB
 Answer the following questions
 What does psychophysics study?
 What is a sensation?
 What is a perception?
 Explain the difference between absolute threshold and difference
threshold.
 What is Webster’s law?
 How can our bodies use sensory adaptation?
 It's easy to make a model of the eardrum (also called the "tympanic
membrane") and see how sound travels through the air. Just stretch a
piece of plastic wrap over a large bowl or pot (any container with a
wide opening will work). Make sure the plastic wrap is stretched tightly
over the container. The plastic represents the eardrum. Place about 20 30 grains of uncooked rice on the top of the plastic wrap. Now you
need a noise maker. A tin cookie sheet or baking tray works well. Hold
the cookie sheet close to the plastic wrap. Hit the cookie sheet to
create a "big bang" noise and watch the rice grains jump.
 The "big bang" produces sound waves (changes in air pressure) that
cause the plastic sheet to vibrate which causes the rice grains to move.
Sound waves vibrate the eardrum in much the same way.
 Materials:
 Plastic wrap
 Container with wide opening
 Uncooked rice (any other small grain will work)
 Tin cookie sheet (or other noise maker)
8.2- The senses
8.1
The Disappearing Circle
Sensation depends on change and contrast in the environment. Hold your hand over one
eye and stare at the dot in the middle of the circle on the right. You should have no
trouble maintaining the image of the circle. If you do the same with the circle on the left,
however, the image will fade. The gradual change from light to dark does not provide
enough contrast to keep the visual receptors in your eye firing at a steady rate. The circle
reappears only if you close and reopen your eye or you shift your gaze to the X.
FIGURE 4
The Stroop Effect
Try to name the colors of the boxes in a as fast as you can. Then try to read the words in b
as fast as you can. Finally, try to name the colors of the words in b as fast as you can. You
probably proceeded more slowly when naming the colors in b.
SECTION 2-OBJECTIVES
• Describe the nature and function of the
sense organs.
• Identify the skin and body senses and
explain how they work.
PAGE 215- 220 IN YOUR BOOK
 Define the following words




Pupil
Lens
Retina
Optic Nerve
 Label the human eye
 Label the human ear
Vision
SECTION 2
• How does vision occur?
– Light enters the eye through the pupil
and reaches the lens, which focuses
light on the retina.
– The retina contains two types of lightsensitive receptor cells, or
photoreceptors: rods and cones.
The Human Eye
Vision (cont.)
SECTION 2
– Rods: sensitive to much lower levels of
light and are the basis for night vision.
– Cones: work best in the daylight and are
sensitive to color.
–When some or all of a person’s cones
do not function properly, he or she is
said to be color deficient.
– These create impulses, that travel along
the optic nerve to the brain, where they
are routed to the occipital lobe.
COLOR BLIND TEST
FIGURE 5
The Human Eye
This cross section of the human eye shows
the passage of light. Note that
the retina receives an inverted image.
BLIND SPOT TEST
Vision (cont.)
SECTION 2
• Binocular fusion—the process of
combining the images received from the
two eyes into a single, fused image.
• There is a difference between the images
on the retinas, called retinal disparity.
Vision (cont.)
SECTION 2
• Nearsightedness—having an eyeball that
is too long, which causes problems seeing
objects that are distant.
• Farsightedness—having an eyeball that is
too short, which causes problems seeing
up close.
FIGURE 7
A Changing Flag
Stare steadily at the lowest
right-hand star for about 45
seconds. Then stare at the
blank space to the left. You
should see a negative
afterimage of this figure. This
occurs because the receptors
for green, black, and yellow
become fatigued or neuronal
firing rates shift, allowing the
complementary colors of each
to predominate when you stare
at the white paper.
Hearing
SECTION 2
• Hearing is caused by sound waves that
pass through various bones until they
reach the inner ear, which contains tiny
hairlike cells that move back and forth.
• These hair cells change sound vibrations
into neuronal signals that travel through
the auditory nerve to the brain.
FIGURE 9
The Human Ear
The earflap funnels sound waves down the ear canal to the eardrum. The bones of the
middle ear pick up the vibrations and transmit them to the inner ear.
Hearing (cont.) SECTION 2
• The auditory nerve carries impulses from
the inner ear to the brain, resulting in the
perception of sound.
– Sound pressure energy is measured in
decibels.
FIGURE 8
Decibel Levels
The loudness of a second (its
amplitude) is measured in
decibels. Each increase of 10
decibels makes a sound 10
times louder. A normal
conversation at 3 feet measures
about 60 decibels, which is
10,000 times louder than a
whisper of 20 decibels. Sound
becomes painful at 130
decibels.
Hearing (cont.) SECTION 2
• Two types of deafness:
– Conduction deafness- anything hinders
physical motion through the outer or middle ear,
or when bones in middle ear become ridged
and cannot carry sound
–Hearing aid can help this by detecting sound
waves
– Sensorineural deafness- occurs from damage
to the cochlea, hair cells, or auditory neurons.
–Hearing aid can typically not help this, a
cochlea implant possibly can
10 QUESTIONS
 Do vision tests first
SECTION 2
Balance
• The body’s sense of balance is regulated
by the vestibular system inside the inner
ear.
• Kinesthesis cooperates with the
vestibular and visual senses to maintain
posture and balance.
•muscles, tendons, and joints that send
messages to the brain upon movement.
SECTION 2
Smell and Taste
• Smell and taste are referred to as the
chemical senses because their receptors
are sensitive to chemical molecules.
• In order to smell, the appropriate gaseous
molecules must come into contact with the
smell receptors in your nose.
• These receptors send messages about
smells through the olfactory nerve to the
brain.
SECTION 2
Smell and Taste (cont.)
• Olfactory nerve—the nerve that carries
smell impulses from the nose to the brain.
• In order to taste, appropriate liquid
chemicals must stimulate receptors in the
taste buds on your tongue.
• Taste information is relayed to the brain,
along with data about the texture and
temperature of the substance in your
mouth.
SECTION 2
• Four primary sensory experiences—sour,
salty, bitter, and sweet—make up taste.
• Smell plays a large role in taste.
• The combination of taste, smell, and tactile
sensations is known as flavor.
The Human Tongue
FIGURE 10
The Human Tongue
When you chew, chemicals of the food mix
with saliva and run down into trenches in
your tongue. Once there, taste buds react to
chemicals dissolved in saliva.
SECTION 2
The Skin Senses
• Receptors in the skin are responsible for
sensing pressure, warmth, cold, and pain.
SECTION 2
The Skin Senses (cont.)
• There are two types of pain sensations:
– The sharp, localized pain you may feel
immediately after an injury.
– The dull, generalized pain you may feel
later.
SECTION 2
The Skin Senses (cont.)
• Gate control theory of pain: we can lessen
some pains by shifting our attention away
from the pain impulses.
• This limits the number of impulses that can
be transmitted, and can dull the pain.
Can you trust your eyes?
THE STROOP TEST – PART 1
Say the name of the color of
each square from left to right
as quickly as you can.
3 VOLUNTEERS
STROOP TEST - PART 2
Say the name of the color of
the following words as quickly
as you can.
THE STROOP TEST – PART 3
Say the name of the color of
the following words as quickly
as you can – again.
8.3-
JOURNAL #2
 Listen to Sophie’s poem
 Follow up to “The Eyes of Me”
 What does the title of the documentary mean?
 What was the most surprising thing you saw or learned in the
documentary?
 What do you think would be most dif ficult about being blind?
What would you miss seeing the most?
 Which of the teenagers was most relatable to you? Why?
 If you were blind, what would the eyes of you be?
SECTION 3-OBJECTIVES
• Outline the principles involved in
perception.
• Describe how we learn to perceive and
what illusions are.
SECTION 3-POLLING QUESTION
Which of the following phone numbers
are you more likely to remember?
A. 555-723-9927
B. 555748975
C. 5 5 5 8 84 98 74
D. 55-5879-5178
8.3- PERCEPTION
 Perception- Brain receives information from the senses and
organizes and interprets it into meaningful experiences
 Perceptual thinking is essential for us to adapt to change
 We don’t just see colors, hear noises, feel temps, etc., we see
cars, buildings, hear voices, music, etc.
SECTION 3
Principles of Perceptual Organization
• The brain makes sense of the world by
creating whole structures out of bits and
pieces of information in the environment.
• Gestalt- whole is more important than
the sum of its parts
SECTION 3
Principles of Perceptual Organization
• Principles used in organizing patterns
include:
– Proximity-similar objects seen as a group
(cont.)
– Continuity- We see continuous patterns, not disrupted ones
– Similarity-similar and dissimilar objects mixed up, we see in
groups
– Simplicity - We see the most simple shapes possible
– Closure- familiar patterns appear, even when pieces are
missing
FIGURE 11
Gestalt Principles
Humans see patterns and groupings in their environment rather than disorganized arrays
of bits and pieces.
SECTION 3
Figure-Ground Perception
• Figure-ground perception is the ability to
discriminate properly between a figure and
its background.
• It is applicable to both sight and hearing.
FIGURE 12
What Is It?
What did you see the first time you looked
at this illustration—a vase or two profiles?
People invariably organize their
experience into figure and ground.
SECTION 3
Perceptual Inference
• Perceptual inference—filling in the gaps
based on past experiences with our
senses.
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what I was Rdanieg. The phaonmneal pweor of
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Cmabrigde Uinervtisy.
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word are, the olny iprmoatnt tihng is that the frist
and lsat ltteer be in the rghit pclae.
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raed it wouthit a porbelm.
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ervey lteter by istlef,
But the word as a wlohe. Amzanig huh? Yaeh
and I awlyas tghuhot slpeling
was ipmorantt!
SECTION 3
Learning to Perceive
• An active involvement in one’s environment
is important for accurate perception.
• We must learn to perceive.
• This learning process is influenced by our
needs, beliefs, and expectations.
• Perceptual set—the idea that we see what
we want to see.
•Ex.- old lady and wallet
FIGURE 14
The Necker Cube
The Necker cube is an ambiguous figure. You can will yourself to see it as if you were
looking down on it, with corner X closest to you, or as if you were looking up at it, with
corner Y closest to you.
FIGURE 13
Pop-Out Features
Reality is a jumble of sensations and details. The letter P probably pops out to you. The Qs
may also pop out, but not as much as the P. You may not have noticed the O, though.
SECTION 3
Learning to Perceive (cont.)
• Subliminal perception—the ability to notice
stimuli that affect only the unconscious
mind.
•Ex.- Movie theater and coke sales
• Subliminal messages- brief auditory or
visual messages that are presented
below the absolute threshold
SECTION 3
Depth Perception
• Depth perception is the ability to recognize
distances and three-dimensionality.
•Develops during infancy
• Monocular depth cue—a cue that can be
used with a single eye to perceive distance
and depth.
8.3
 Monocular cues
SECTION 3
Depth Perception (cont.)
• Monocular depth clues include:
– Relative height
– Interposition- overlapping images
– Light and shadows
– Texture-density gradient- farther an object is, less
detail we see
– Motion parallax- apparent movement of stationary
objects relative to one another
– Linear perspective
SECTION 3
Depth Perception (cont.)
• Binocular depth cue—a cue that depends
upon the existence or movement of both
eyes.
SECTION 3
Depth Perception (cont.)
• Binocular depth cues include:
– Convergence- eyes turn inward to see close object
– Retinal disparity- two images into one
SECTION 3
Constancy
• Constancy is the tendency to perceive
certain objects in the same way regardless
of changing angle, distance, or lighting.
Shape Constancy
We perceive the opening
door as being rectangular
in shape, although our
view of the shape of it
changes as it opens.
SECTION 3
• Illusions are incorrect perceptions that
are created when perceptual cues are
distorted.
FIGURE 16
Lines of Different Lengths?
The lines between the arrowheads in (a) are exactly the same length, as are the heavy
black lines in (b). Some psychologists believe that the reason the lines in (a) seem of
different lengths is because they are interpreted as offering different cues to their
distance from the viewer. The lines in (b) may appear to be different in length because the
brain interprets this diagram as though it is from a scene such as that in (c).
SECTION 3
Extrasensory Perception
• Extrasensory perception (ESP) includes
the following four types:
– Clairvoyance-perceiving objects with no sensory input
– Telepathy- Reading someone’s mind or transferring thoughts
– Psychokinesis- moving objects through mental effort
– Precognition- Ability to foretell events