5th Edition
Psychology
Stephen F. Davis
Emporia State University
Joseph J. Palladino
University of Southern Indiana
PowerPoint Presentation by
Cynthia K. Shinabarger Reed
Tarrant County College
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Copyright © Prentice Hall 2007
3-1
Chapter 3
5th Edition
Sensation and
Perception
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3-2
Sensation, Perception, and
Psychophysics
• Sensation is the activation of receptors by
stimuli in the environment.
• Sensations are the basic building blocks of
perception.
• Perception is the process of organizing
and attempting to understand the sensory
stimulation we receive.
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3-3
Sensation, Perception, and
Psychophysics
• To activate a particular receptor, a specific
type of energy must be present—light
waves for vision, movement of air
molecules for hearing, molecules in a
liquid solution for taste, and so forth.
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Sensation, Perception, and
Psychophysics
• Transduction is the process by which the
receptors change the energy they receive
into a form that can be used by the
nervous system.
• Adaptation occurs when continued
presentation of the same stimulus results
in a loss of sensitivity to that stimulus.
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Sensation, Perception, and
Psychophysics
• Psychophysicists, such as Ernst Weber
and Gustav Fechner, studied the
relationship between the mind and the
body.
• Weber’s law is the observation that the
amount of stimulus increase or decrease
required to notice a change, divided by the
original stimulation, is a constant.
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Sensation, Perception, and
Psychophysics
• The just noticeable difference (jnd) is
the smallest difference between two
stimuli that is noticeable 50% of the time
by participants.
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Sensation, Perception, and
Psychophysics
• Gustav Fechner studied both the absolute
threshold and the differential threshold.
• The absolute threshold is the minimum
amount of energy required for conscious
detection of a stimulus 50% of the time by
participants.
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Sensation, Perception, and
Psychophysics
• To determine the differential threshold or
jnd, we investigate the amount of stimulus
energy that must be added to or
subtracted from an existing stimulus for a
participant to notice a difference (that is, to
produce a just noticeable difference) 50%
of the time.
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3-9
Sensation, Perception, and
Psychophysics
• Signal detection theory, or the
contention that the threshold varies with
the nature of the signal and noise, was
developed to explain the difficulties one
might encounter in distinguishing a certain
stimulus from the background or noise.
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Sensation, Perception, and
Psychophysics
• Subliminal stimuli are stimuli that are
below the threshold of consciousness.
• Although a limited number of
presentations of a subliminal stimulus may
not alter our behaviors dramatically and
immediately, there is some evidence that
repeated subliminal presentations may
change our attitudes and opinions.
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3-11
Sensory Systems
• Vision is a process that involves the reception of
electromagnetic waves by visual receptor cells.
• This kind of energy travels in waves that vary
greatly in length.
• We measure wavelengths, or the length of
waves, in nanometers (nm), which are billionths
of a meter.
• The only light waves that humans can detect
have wavelengths between approximately 380
and 760 nm.
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Sensory Systems
• This limited range of stimuli (the human
eye can see only a small portion of the
spectrum) is called the visible spectrum.
• Different light wavelengths are associated
with different colors.
• Amplitude refers to the strength or
intensity (brightness) of the light.
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Sensory Systems
• Saturation refers to the “trueness” or
purity of the colors we perceive.
• With radiant light, visible energy is
emitted (released) directly by an object.
• With reflected light, by contrast, energy is
reflected by objects.
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Sensory Systems
• If a surface reflects only one wavelength,
the color you perceive is pure.
• The degree of purity decreases as the
number of different, reflected wavelengths
increases.
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3-16
Sensory Systems
• Vision involves a complex chain of events.
• Initially, light waves pass through the
protective cornea.
• In addition to its protective function, the
cornea helps focus the light waves.
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Sensory Systems
• After striking the cornea, light waves enter
an open area called the anterior chamber.
• Here they pass through the aqueous
humor, a clear watery fluid.
• Then the light waves are funneled through
the small opening known as the pupil.
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Sensory Systems
• The pupil is surrounded by a colored
membrane, the iris, which changes shape
(like the diaphragm of a camera) to
regulate the size of the pupil and therefore
the amount of light taken in.
• Next, the light passes through the lens.
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Sensory Systems
• The lens, which is supported by two
powerful ciliary muscles, is elastic; it can
change shape to focus the visual image.
• Changing the shape of the lens to focus is
known as accommodation.
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Sensory Systems
• After passing through the lens, the light
waves enter a second, larger open space
called the posterior chamber.
• Finally, the light waves strike the retina,
the light-sensitive tissue at the back of the
eye that contains the visual receptors
(rods and cones).
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Sensory Systems
• The retina is made up of several layers:
the three major layers are the ganglion cell
layer, the bipolar cell layer, and the
photoreceptor layer.
• After light strikes the surface of the retina,
it must travel through several layers of
cells before it activates the visual
receptors, which make up the back layer
of the retina.
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Structures of the Eye
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3-23
Sensory Systems
• Light waves cause the receptors to
change their electrical charge.
• If that change is great enough, the bipolar
cells fire.
• If enough bipolar cells fire, the next layer
of cells, the ganglion cells, fires.
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Layers of Cells in the Retina
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Sensory Systems
• The axons of the ganglion cells come
together to form the optic nerve, which
carries visual information to higher brain
centers.
• At the point where the axons of the
ganglion cells come together and leave
the eyeball, there are no receptors.
• This area is known as the blind spot.
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Sensory Systems
• The optic nerves from each eye join at the
optic chiasm, which is located on the
underside of the brain, just in front of the
pituitary gland.
• The fibers from the nasal half (closest to
the nose) of the retina cross to the
opposite hemisphere; those from the
peripheral (outlying) half of each retina
continue to the hemisphere on the same
side of the body.
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Sensory Systems
• The next stop is an area in the thalamus,
the relay station in the forebrain.
• Ultimately, the visual information is
received by the occipital lobe of the cortex,
where higher-level visual processing
begins.
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The Visual Pathway
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Sensory Systems
• The rods (120 to 125 million per eye) are
the most prevalent visual receptors.
• They have a lower threshold and lower
acuity (sharpness of perception) than
cones and do not detect color.
• By contrast, the cones (6 to 7 million) are
less prevalent, have a higher threshold
and higher acuity, and are able to detect
color.
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Sensory Systems
• The rods are slender and cylindrical,
whereas the cones are much broader.
• Most of the cones are found in one area,
the fovea, an indented spot in the center
of the retina. Both the rods and cones
contain light-sensitive chemicals called
photopigments.
• When light strikes the rods and cones, it
causes a chemical reaction in these
photopigments.
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Sensory Systems
• Two theories of color vision have been
formulated.
• The trichromatic theory proposes that
there are three different types of color
receptors.
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Sensory Systems
• The opponent-process theory stresses the
pairing of color experiences; activation of one
process can inhibit its partner.
• Both theories are supported by research
findings.
• Opponent-process cells may also be responsible
for the production of color afterimages.
• A color afterimage is the perception of a color
that is not really present; it occurs after viewing
the opposite or complementary color.
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Sensory Systems
• People who suffer deficits in color vision
are said to be color deficient.
• Monochromats are unable to see color.
• Dichromats lack the ability to see one of
the three primary colors (red, blue, or
green).
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Sensory Systems
• Audition is the sense of hearing.
• Just as we see light waves, we hear sound
waves.
• A sound wave is essentially moving air.
• Like light waves, sound waves have three
distinct characteristics: wavelength
(frequency), amplitude (intensity), and
purity (also known as timbre).
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Sound Waves
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Sensory Systems
• Frequency is measured in cycles per
second and expressed in hertz (Hz).
• As with light waves, the amplitude, or
height, of the sound wave affects its
intensity.
• Greater amplitude results in a more
intense sound.
• The amplitude of sound waves is
measured in decibels (db).
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Sensory Systems
• Decibel levels represent the amount of
energy producing the pressure of the
vibrations we perceive as sound; the
greater the pressure, the stronger or more
intense the vibration.
• The purity or timbre of a sound wave can
be measured, but we do not experience
many pure tones in our lifetimes.
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Sensory Systems
• Like the visual receptors, the auditory
receptors are sensitive to a limited range
of sound waves.
• Basically, we hear sounds with
wavelengths between 20 and 20,000 Hz.
• Our hearing is more acute at 1,000 Hz;
greater intensity (amplitude) is required if
we are to hear tones at lower and higher
frequencies.
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3-39
Sensory Systems
• The auditory system is divided into three
components: the outer ear, the middle ear, and
the inner ear.
• The outer ear, especially the pinna, gathers
sound waves and starts them on their way to the
auditory receptors.
• The sound waves are then funneled down the
auditory canal.
• Ultimately they strike the eardrum and cause it
to move.
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Sensory Systems
• Movement of the eardrum in turn causes
the three bones (hammer, anvil, and
stirrup) of the middle ear, collectively
called the ossicles, to vibrate.
• The hammer (malleus), which is attached
to the eardrum, strikes the anvil (incus).
• The anvil in turn strikes the stirrup
(stapes).
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Sensory Systems
• The stirrup is connected to the oval window,
which connects the middle ear to the snailshaped cochlea of the inner ear.
• When the stirrup causes the oval window to
vibrate, fluid located in the cochlea is set in
motion.
• The motion of the fluid produces vibration in the
basilar membrane.
• This vibration in turn causes the organ of Corti,
which rests on it, to rise and fall.
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Sensory Systems
• When the organ of Corti moves upward,
the hair cells that project from it brush
against the tectorial membrane located
above it.
• The hair cells are the auditory receptors
where transduction occurs.
• Contact with the tectorial membrane
causes them to bend; when they bend,
they depolarize.
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Sensory Systems
• Sufficient depolarization of the auditory
receptors causes the neurons that
synapse with them to fire.
• The axons of these neurons come
together before they leave the cochlea to
form the auditory nerve, which transmits
auditory information to higher brain
centers.
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Sensory Systems
• From the cochlea, the auditory nerve
travels to the medulla, where some fibers
cross to the opposite hemisphere.
• The next stop is the thalamus.
• Ultimately the information reaches the
temporal lobe of the cortex for processing.
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The Auditory System
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Sensory Systems
• At present, there are two theories to
explain how we hear different tones or
pitches.
• The older place theory, proposed by
Hermann von Helmholtz in 1863, says that
hair cells located at different places on the
organ of Corti transmit information about
different pitches.
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Sensory Systems
• The place theory says that what you hear
depends on which hair cells are activated.
• For this theory to be correct, the basilar
membrane has to vibrate in an uneven
manner, which is exactly what happens
with frequencies above 1,000 Hz.
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Sensory Systems
• The frequency theory of Ernest Rutherford
applies to frequencies below 1,000 Hz.
• In 1886, Rutherford suggested that we perceive
pitch according to how rapidly the basilar
membrane vibrates.
• The faster the vibration, the higher the pitch, and
vice versa.
• The frequency theory works fine with
frequencies up to 100 Hz; typically, however,
neurons do not fire more than 100 times per
second.
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Sensory Systems
• According to the volley principle, at
frequencies above 100 Hz auditory
neurons do not all fire at once; instead,
they fire in rotation or in volleys.
• Two mechanisms help us locate the
source of a sound.
• The first is blockage of certain sounds by
the head.
• The second mechanism is time delay in
neural processing.
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Sensory Systems
• Several hearing problems have been
studied extensively: conduction deafness,
sensorineural deafness, and central
deafness.
• The first two may be caused by exposure
to very loud noises.
• Conduction deafness refers to problems
associated with conducting or transmitting
sounds through the outer and middle ears.
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Sensory Systems
• In addition to excessive exposure to loud noises
that can cause the eardrum to burst, common
causes of conduction deafness are excessive
ear wax or damage to the hammer, anvil, or
stirrup.
• Sensorineural deafness is caused by damage
to the inner ear, especially the hair cells.
• Central deafness is caused by disease and
tumors in the auditory pathways and auditory
cortex of the brain.
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Sensory Systems
• Gustation refers to the sense of taste.
• The stimuli for taste are molecules dissolved in a
liquid.
• Once molecules are in solution, they can come
into contact with the taste receptor cells, which
are located in structures known as taste buds.
• Each taste bud contains between 50 and 100
taste receptors.
• The taste buds line the walls of small bumps on
the tongue and throat called papillae.
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Sensory Systems
• Individual taste receptor cells do not last
forever; with a life expectancy of only 10
days to 2 weeks, the cells within a taste
bud are continually being replaced.
• The number of taste buds increases
during childhood to a maximum of about
10,000.
• At approximately age 40 the trend
reverses and our sense of taste declines.
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Sensory Systems
• Although researchers are not absolutely
sure how taste receptors work, the most
credible theories advanced to date
suggest that molecules in the solution
attach to or fit into receptor sites.
• The actual taste receptor sites are located
on microscopic hairs, known as microvilli,
that project from the tips of the taste
receptor cells.
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Sensory Systems
• The receptor sites have different
geometric shapes or different types of ion
channels, so the shape of the molecule
determines whether it fits into a specific
receptor site.
• For nearly a century, researchers have
agreed with the proposal that we are
sensitive to at least four primary tastes:
sweet, sour, bitter, and salty.
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Sensory Systems
• In the late 1990s, receptor sites for a fifth taste,
umam (savory or meaty), were identified;
however, researchers are not in complete
agreement that umami really is a separate taste.
• Hence it is reasonable to suppose that there are
at least four different types (shapes) of receptor
sites.
• Once the sites are occupied, depolarization
occurs and information is transmitted through
the gustatory nerve to the brain.
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Sensory Systems
• The gustatory nerve goes from the taste
buds to the medulla in the hindbrain,
where they synapse.
• From there the information travels to the
thalamus and is then relayed to the
somatosensory cortex in the forebrain.
• At this point, you are able to determine the
nature of the taste you have experienced.
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Sensory Systems
• Olfaction refers to the sense of smell.
• Odors are produced by molecules in the air.
• More than 2 million Americans have a significant
loss in the ability to smell.
• This condition, called anosmia, can result from
genetic defects, aging, viruses, allergies, or
certain prescription drugs.
• The most common cause, however, is head
trauma, which can shear off axons that run from
the olfactory nerves to the brain.
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Sensory Systems
• The nose does not contain the olfactory
receptors; its function is to collect and filter
the air we breathe.
• The olfactory receptors are located in an
area of tissue of about 2.5 cm (1 in.)
square in each nasal cavity.
• We have about 10 million olfactory
receptors, each of which has 6 to 12 hairlike projections called cilia.
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Sensory Systems
• Like taste receptors, olfactory receptors are
continually dying and being replaced.
• The life span of an olfactory receptor is about 5
to 8 weeks.
• There may be as many as 1,000 different types
of olfactory receptor sites.
• Although researchers do not know a great deal
about how they work, the olfactory receptors
appear to operate under the same type of lockand-key/pattern recognition principle as the taste
receptors.
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Sensory Systems
• The olfactory nerve takes a somewhat different
route to the brain from the other senses.
• The first step is a synapse in the olfactory bulb,
which is located near the optic chiasm on the
underside of the brain.
• From there, some of the olfactory nerve fibers go
to the amygdala.
• From the amygdala, the olfactory nerve travels
to the thalamus and hypothalamus and then on
to the cerebral cortex for higher-level
processing.
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Olfaction
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Sensory Systems
• One set of researchers reported the results of an
experiment that proved the interdependence of
smell and taste in experiencing a flavor.
• In this study they placed a drop of a certain
flavor on a participant’s tongue and asked the
person to identify the taste.
• When participants could smell normally, they
were correct on most tries; when the
experimenter prevented them from smelling,
however, they were often unable to identify it.
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Sensory Systems
• The vestibular sense, which originates in
the inner ear, provides information about
the body’s orientation and movement.
• The vestibular system consists of the three
semicircular canals in the inner ear and
the utricle.
• The semicircular canals are located at
right angles to each other to provide
information about movement in all
directions.
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Sensory Systems
• Each semicircular canal is filled with a jellylike
fluid that moves as the head moves.
• Movement of the fluid in the canal causes hair
cells located in the canal to bend.
• Bending the hair cells sends information about
movement to the brain.
• The utricle, a fluid-filled chamber also located in
the inner ear, operates on the same principle as
the semicircular canals and serves as a gravity
detector.
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Sensory Systems
• The kinesthetic sense is a system of receptors
located in the muscles and joints that provides
information about the location of the extremities.
• Sense receptors located in the joints and
muscles send information to the brain
concerning muscle tension and joint position.
• The brain combines this information with other
sensory input, such as vision and audition, to
help you determine the location of your limbs.
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Sensory Systems
• Cutaneous senses
refers to a system
of receptors located
in the skin that
provides
information about
touch, pressure,
pain, and
temperature.
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Sensory Systems
• The wide variety of skin receptors for
touch or pressure are called
mechanoreceptors; the receptors for
temperature are called thermoreceptors.
• The general term for receptors that
respond to painful stimuli is
nocioreceptors.
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Sensory Systems
• One theory of pain, the gate control theory,
has greatly influenced our understanding of
pain. According to this theory, pain impulses are
transmitted from the receptors (free nerve
endings) to the spinal cord.
• The axons of the pain neurons release
substance P in the spinal cord.
• In turn, substance P causes neurons in the
spinal cord to send information about pain to the
brain for processing and perception.
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Sensory Systems
• Thus the painful stimulus, in conjunction
with substance P, opens the pain gate.
• Neurons that descend from the brain to
the spinal cord release opioid peptides
called endorphins.
• In turn, the endorphins block the release of
substance P and the pain gate is closed.
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Perception
• We do not perceive everything in our
environment; our motives greatly influence
our perceptions.
• Similarly, certain stimuli are more likely
than others to attract our attention.
• In dichotic listening experiments, a
different message is presented to each of
a participant’s ears, and the participant is
asked to recall both messages.
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Perception
• Dichotic listening tasks are designed to study
divided attention, the ability to attend to more
than one message or type of information at the
same time.
• Research in this area has uncovered some
intriguing information about human perception.
• For example, we hear (and understand) much
more than the information of which we are
consciously aware as illustrated by the “cocktailparty phenomenon.”
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Perception
• In addition to needs, motives, and prejudices,
certain aspects of stimuli determine which ones
get our attention.
• For example, people generally pay more
attention to stimuli that are larger, louder, or
more colorful than others.
• When something happens unexpectedly, our
attention is attracted very quickly.
• When contrast and surprise combine, our
attention is commanded even more quickly.
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Perception
• The ability to discriminate among shapes and
figures is known as pattern perception.
• The feature analysis theory states that we
perceive the elements of an object and then
combine them to produce our perception of
the object (bottom-up processing).
• Research suggests that, at least in some
instances, we use a top-down approach in
which the whole object is recognized before
its component parts are identified.
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Perception
• Perceptual constancy is the tendency to
perceive the size and shape of an object
as constant even though its retinal image
changes.
• Shape constancy means that your
perception of the shape of an object as
viewed from different angles does not
change even though the image projected
on your retina does so.
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Perception
• Size constancy is the tendency to
perceive the size of an object as constant
despite changes in its retinal image.
• Depth perception is the ability to perceive
our world three-dimensionally.
• Two main types of cues, binocular and
monocular, are used to create our
perception of depth.
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Perception
• Binocular cues require the integrated use
of both eyes, whereas monocular cues
are effectively processed using information
from only one eye.
• Two binocular cues are adjustments of the
eye muscles (a weak/nonprecise cue) and
binocular disparity.
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Perception
• If you open and close one eye and then the
other, it is obvious that you do not see exactly
the same thing with each eye.
• The closer the object, the greater the difference
between what the two eyes see.
• This difference occurs because each eye sees
from a different angle, a phenomenon known as
binocular disparity.
• When the images from both eyes merge in the
brain, a sense of depth is created.
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Perception
• Monocular cues of depth include
– interposition (near objects partially obscure
more distant objects),
– texture gradient (the texture of a surface
becomes smoother with increasing distance),
– linear perspective (parallel lines appear to
converge as they recede into the distance),
and
– relative brightness (brighter objects appear
closer than duller-appearing ones).
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Perception
• The Gestalt psychologists demonstrated
that we actively organize our perceptual
world into meaningful groups or wholes.
• Figure–ground relation is the
organization of perceptual elements into a
figure (the focus of attention) and a
background.
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Perception
• Several conditions promote the grouping
of perceptual elements.
• With proximity, items that are close to
each other are perceived as a group.
• According to the Gestalt principle of
similarity, items that are alike are
grouped together: XXXOOO, is perceived
as three Xs and three Os.
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Perception
• The Gestalt principle of good
continuation says that we perceive
continuous, flowing lines more easily than
choppy or broken lines.
• The Gestalt principle of closure says that
organizing our perceptions into complete
objects is easier than perceiving each part
separately.
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Perception
• Apparent motion is the illusion of
movement in a stationary object.
• Perceptual hypotheses are inferences
about the nature of stimuli received from
the environment.
• Perceptual illusions are misperceptions
or interpretations of stimuli that do not
correspond to the sensations received.
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Perception
• Recent advances in the study of brain
functioning promise to change our conception
of sensory processes and perception.
• For example, studies of the human visual
cortex indicate that sensory processing does
not occur in a strictly sequential manner where
one part of the brain performs an activity and
then passes the modified sensation on to
another brain area for additional processing.
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Perception
• The picture that emerges is of a parallel
processing system in which information
simultaneously flows both from lower to
higher levels and from higher to lower
levels in the brain.
• For example, exciting breakthroughs also
are occurring in the study of higher-level,
more cognitive processes, such as visual
search.
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Perception
• Visual search is the process of identifying the
presence or absence of a target stimulus among
a group of distractor items.
• Research on this topic shows that when stimuli
have high salience (that is, when they are
relevant, meaningful, or distinctive), visual
search is done efficiently, rapidly, and in a
parallel manner.
• Indeed, such high-salience stimuli seem to “pop
out” from the distractors.
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Perception
• Perception may be influenced by the
social context.
• For example, the Ebbinghaus illusion is
influenced by the type of social stimuli
used.
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Paranormal Phenomena
• Extrasensory perception (ESP) refers to
behaviors or experiences that cannot be
explained by information received from the
senses.
• The term ESP is reserved for paranormal
phenomena that do not involve the senses.
• The most frequently mentioned examples of
ESP are clairvoyance, telepathy, and
precognition.
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Paranormal Phenomena
• Clairvoyance is the claimed ability to “see”
information from objects or events without
direct contact with the senses.
• Telepathy is the claimed ability to perceive
the thoughts or emotions of others without
the use of recognized senses.
• Precognition is knowledge of a future
event or circumstance obtained by
paranormal means.
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Paranormal Phenomena
• Psychokinesis (once known as telekinesis) is the
claimed power of the mind to influence matter
directly.
• Because psychokinesis does not involve
perception, some researchers do not consider it
an example of ESP.
• The term parapsychology is often used to refer
to “the study of paranormal phenomena, which
are considered to be well outside the bounds of
established science.”
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Paranormal Phenomena
• The claims offered by supporters of ESP
are sometimes presented in ways that
make designing a definitive test difficult, if
not impossible.
• Most scientists agree that allegedly
paranormal phenomena can be explained
without resort to non-normal evidence.
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Paranormal Phenomena
• Many people have psychic experiences, or at
least experiences they interpret as such.
• Psychologists suggest that paranormal
experiences are an inevitable consequence of
the way we perceive and remember
information.
• We can be fooled by our experiences in much
the same way we are fooled by the visual
illusions described earlier.
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Paranormal Phenomena
• Although the methods of studying
paranormal phenomena have improved,
“the goal of a conclusively convincing
demonstration or a repeatable experiment
has not been achieved.”
• Should we therefore dismiss even the
possibility of paranormal phenomena?
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Paranormal Phenomena
• Before we do, let’s consider an important
history lesson: some phenomena that in
the past were considered to be
paranormal, impossible, or even fraudulent
have since been verified to be real.
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