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Sensation &
Perception
Chapter 8
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Section 1
• Sensations allow humans to understand
reality. Sensations occur anytime a stimulus
activates a receptor.
• Objectives
• Describe the field of study known as
psychophysics
• Define and discuss threshold, Weber’s law and
signal detection
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Discovering a New World
• Helen Keller- discovered new ways to
experience the world
• She entered a world of sensations after she
began organizing the stimuli in her world
• Try it yourself
3
Read This
• In the next few seconds, something
peculiar will start hap pening to the
material youa rereading. Iti soft
ennotre alized howcom plext heproces
sof rea ding is.
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Organization
• Your success in gathering information from
your
environment,
interpreting
this
information, and acting on it depends
considerably on its being organized in ways
you expect.
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Stimulus
• The world is filled with physical changes
• alarm clock sounds, switch flips on a bright
light, you stumble against a door
• Stimulus- any aspect of or change in the
environment to which an organism responds
• alarm clock, electric light, sore muscles
• can be measured in many physical ways
• Size, duration, intensity or wavelength
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Sensation
• Sensation- occurs anytime a stimulus
activates one of your receptors
• Sense organs detect physical changes in
energy such as heat, light, sound, and
physical pressure
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Perception
• Perception- the organization of sensory
information into meaningful experiences
• A sensation may be combined with other
sensations and your past experience to yield
a perception
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Psychophysics
• The psychological study of such questions as
• What is the relationship btw color and
wavelength?
• How does changing a light’s intensity affect your
perception of its brightness?
• The goal of the study is to understand how
stimuli from the world (such as frequency and
intensity) affect the sensory experience (such as
pitch and loudness) produced by them
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Threshold
• In order to establish laws about how people
sense the external world, psychologists first
try to determine how much of a stimulus is
necessary for a person to sense it at all
• How much of a scent must be in a room
before one can smell it?
• How much energy is required for someone
to hear a sound or to see a light?
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Threshold Experiment
• Participant is place in a dark room and
instructed to stare at a blank wall
• Instructed to say “I see it” when he is able
to detect a light
• Psychologist uses an extremely precise
machine that can project a low-intensity
beam of light against the wall
• Then done in reverse
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Water Check
• Get two different cups of water from the
back of the room.
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Absolute Threshold
• The weakest amount of a stimulus required
to produce a sensation (detected 50% of the time)
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•
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Vision- candle flame 30 miles away
Hearing- watch ticking 20 ft away
Taste- 1 t of sugar in 2 gallons of water
Smell- 1 drop of perfume in a 3-room house
Touch- feeling a bee’s wing falling a distance of
1 centimeter onto your cheek
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Sensory Differences & Ratio
• Difference Threshold
• Refers to the minimum amount of difference a
person can detect between two stimuli half of
the time
• Just Noticeable Difference- JND
• Refers to the smallest increase or decrease in
the intensity of a stimulus that a person is able
to detect
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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
• Backpack p 211
• People who can detect small differences in
sensation work as food tasters, wine tasters,
smell experts, perfume experts …
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Sensory Adaptation
• Senses are most responsive to increases and
decreases, and to new events rather than to
ongoing, unchanging stimulation
• They get used to a new level and respond only
to deviations from it
• Getting used to a dark theater
• Cold swim
• Disagreeable odors
Figure 8.3 on p 212
• Street noises
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• Clothes on your body
Signal-Detection Theory
• The study of people’s tendencies to make
correct judgments in detecting the presence
of stimuli
• Involves recognizing some stimulus against
as background of competing stimuli
Radar operator
• Abandons the idea that there is a single true17
absolute threshold
Processing Stimuli
• Preattentive process- method for
extracting information automatically and
simultaneously when presented with stimuli
• Attentive process- procedure that considers
only one part of the stimuli presented at a
time
Stroop interference effect- preattentive (automatic) processing
acts as an interference. The tendency is to read the word instead
of saying the color on ink p 213 Figure 8.4
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Section 2
• The sense organs- the eyes, tongue, nose,
skin, and others- are the receptors of
sensations
• Objectives
• Describe the nature and functioning of the
sense organs
• Identify the skin and body senses and explain
how they work
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More than five
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Vision
Hearing
Taste
Smell
Touch
Several skin senses
Two internal senses
• Vestibular and Kinesthetic
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Vision
• Most studied of all the senses
• Provides us with a great deal of info abt our
environment
• Sizes, shapes, locations, textures, colors &
distances
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Parts of the Eye
• Pupil- the opening in the iris that regulates
the amount of light entering the eye
• Lens- a flexible, transparent structure in the
eye that changes its shape to focus light on
the retina
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• Retina- the innermost coating of the back of
the eye containing the light- sensitive
receptor cells responsible for changing light
energy into neuronal impulses
• Rods
• Cones
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Cones and Rods
• Cones- require more light to respond
• Best in daylight
• 6-7 million
• Sensitive to color
• Rods- require less light to respond
• Night vision
• 75-150 million
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Color Deficiency
• Figure 8.7 (p 218)
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• Optic Nerve- the nerve that carries impulses
from the retina to the brain
• Blind spot (p 216)
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Light
• Electromagnetic radiation
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•
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Radio waves
Microwaves
Infrared radiation
Ultraviolet rays
X rays
• Prisms
• Electromagnetic Spectrum figure 8.6 (p 217) 27
Hearing
• Depends on vibrations in the air- sound waves
• Sound waves from the air pass through
various bones until they reach the inner ear,
which contains tiny hairlike cells that move
back and forth
• Hair cells change sound vibrations into
neuronal signals that travel through the
auditory nerve to the brain
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Loudness & Strength
• Loudness- determined by the amplitude
(height) of sound waves
• The higher the amp the louder the sound
• Strength- or sound pressure energy is
measured in decibels
• 0 decibels- the softest, anything over 110 can
damage hearing as can persistent sounds as low
as 80
See Figure 8.9
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Pitch
• Depends on sound-wave frequency
• Low frequencies produce deep bass
• High frequencies produce shrill squeaks
• If you hear a sound composed of a
combination of different frequencies, you
hear the separate pitches even though they
occur simultaneously
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Direction
• If a noise occurs on your right, the sound
wave comes to both ears, but it reaches the
right ear a fraction of a second before it
reaches the left
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The Pathway of Sound
• Read p 219
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Conduction Deafness
• Occurs when anything hinders physical
motion through the outer or middle ear of
when the bones of the middle ear becomes
rigid and cannot carry sounds inward
• Can be helped with conventional hearing
aids
• Picks up sound waves, changes them into
vibrations and sends they to the inner ear
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Sensorineural Deafness
• Occurs from damage to the cochlea, the hair
cells of the auditory neurons
• Cannot be helped by traditional hearing aids
• May be helped by a cochlear implant
• Changes sound waves into electrical signals,
these signals are fed into the auditory nerve,
which carries them to the brain
• The brain then processes the sensory input
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Balance
• Read p 220
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Smell
• Chemical sense
• Molecules enter your nose in vapors that
reach a special membrane in the upper part
of the nasal passages on which the smell
receptors are located
• These receptors send messages about smell
through the olfactory nerve to the brain
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Taste
• Chemical sense
• Appropriate chemicals must stimulate
receptors in the taste buds on your tongue
• Taste info is relayed to the brain along with
data about the texture and temperature of
the substance
• 4 primary sensory experiences
• Sour, Salty, Bitter, and Sweet
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• Flavor- the combining of taste, smell and
tactile sensations
• Much of what we think of as taste is really
the sense of smell
• Sensations of warmth, cold, and pressure also
effect taste
• The chemical senses play a lesser role of
pleasure in humans
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The Skin Senses
• Receptors in the skin are responsible for
providing the brain with at least four kinds
of info about the environment
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Pressure
Warmth
Cold
Pain
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Perceptions of Pain
• Pain results from many different stimuli
• Sharp, localized pain you may feel immediately
• Dull, generalized pain you may feel later
• Gate control theory of pain- we can lessen
some pains by shifting our attention away
from the pain impulse
• Rubbing a stubbed toe
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The Body Senses
• Kinesthesis- the sense of movement and
bodily position
• Comes from receptors in and near the
muscles, tendons and joints
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Section 3
Perception
• The way we interpret sensations and
organize them into meaningful experiences
is called perception
• Objectives
• Outline the principles involved in perception
• Describe how we learn to perceive and what
illusions are
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Perception
• The brain receives info from the senses and
organizes and interprets it into meaningful
experiences
• Trying to catch a fly
• Bug detector does not know the eye has been
rotated
• Perception goes beyond reflexive behavior &
allows us to confront changes in our
environment
• Perceptual thinking is essential for us to adapt
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to change
Principles of Perceptual
Organization
• The brain makes sense of the world by
creating whole structures out of bits and
pieces of information
• Gestalt- each whole that is organized by the
brain
• German word meaning pattern or configuration
• The whole is more than the sum of the parts
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Closure
• When we see a familiar pattern or shape
with some missing parts, we fill in the gaps
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Proximity
• When we see a number of similar objects
we tend to perceive them as groups or sets
of those that are close to each other
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Similarity
• When similar and dissimilar objects are
mingled, we see the similar objects as
groups
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Continuity
• We tend to see continuous patterns, not
disrupted ones
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Simplicity
• We see the simplest shapes possible
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Figure-Ground Perception
• The ability to discriminate properly between
a figure and its background
• Important in hearing and vision
• Allows you to follow one person’s voice at a
noisy meeting
• When you listen to a piece of music a familiar
theme jumps out at you
• The melody bcms the figure and the rest of the
music is merely background
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Learning to Perceive
• Perceiving is something that people learn to do
• Influenced by our needs, beliefs, and
expectations
• When we want something, we are more likely
to see it
• Previous experiences influence what we see
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Subliminal Perception
• Subliminal Messages- brief auditory or
visual messages presented below the absolute
threshold so that there is less than 50%
chance that they will be perceived
• James Vicary- Movie messages
• 1/3000 of a second, once every 5 seconds
• Popcorn sales raised 58%, Coke 18%
• Anthony Greenwald- 1990
• Memory and self-esteem tapes/ improvement aft52
1 month
Depth Perception
• Monocular Depth Cues-uses one eye
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Relative height- bigger is nearer
Interposition- overlapping
Light and Shadows- lighter is nearer
Texture-density gradient
• Motion parallax
• Linear perspective
• Relative motion
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• Binocular Depth Cues
• Convergence- process by which your eyes turn inward
to look at nearby objects
• Retinal disparity- bcs each eye occupies a different
position each eye receives a slightly different image
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Constancy
• The tendency t percieve certain objects in
the same way regardless of changing angle,
distance, or lighting
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Illusions
• Illusions- incorrect perceptions
• Created when perceptual cues are distorted
so that our brains cannot correctly interpret
space, size and depth cues
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Extrasensory Perception
• ESP- an ability to gain information by some
means other than the ordinary senses
Next
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• Clairvoyance- perceiving objects or information
without sensory input
• Telepathy- involves reading someone else’s mind
or transferring one’s thoughts
• Psychokinesis- involves moving objects through
purely mental effort
• Precognition- ability to foretell events
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