Sensation and Perception
Book authors:
R.H. Ettinger
Chapter 4
Sensation &
Perception
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Sensation and Perception
 Sensation
– The process through which the senses pick up
visual, auditory, and other sensory stimuli and
transmit them to the brain; sensory information that
has registered in the brain but has not been
interpreted
 Perception
– The process by which sensory information is
actively organized and interpreted by the brain
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Process of Sensation
 Sensory receptors
– Specialized cells in the sense organs that detect
and respond to sensory stimuli—light, sound,
odors—and transduct (convert) the stimuli into
neural impulses
– Provide the essential link between the physical
sensory world and the brain
 Transduction
– Process where the receptors change or convert the
sensory stimulation into neural impulses
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Process of Sensation
 Absolute threshold
– The minimum amount of sensory stimulation that
can be detected 50% of the time
 Difference threshold
– The smallest increase or decrease in a physical
stimulus required to produce a difference in
sensation that is noticeable 50% of the time
– Just noticeable difference (JND)
– The smallest change in sensation that a person is
able to detect 50% of the time
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Process of Sensation
 Ernst Weber
– Observed that the JND for all the senses depends
on a proportion or percentage of change rather than
a fixed amount of change
– Observation known as Weber’s law
– Weber’s law best fits people with average
sensitivities
 Expert wine tasters would know if a particular vintage was
a little too sweet, even if its sweetness varied by only a
fraction of the 20% necessary for changes in taste
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Process of Sensation
Absolute Sensory Thresholds
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Process of Sensation
 Attention
– Psychological selection mechanism that determines which
stimuli an organism responds to or perceives
– Does not block the physical and biological response of our
sense organs to these stimuli only blocks perception
– Cocktail Effect (hearing someone call your name across the
room but not aware of their conversation)
 Sensory adaptation
– The process of becoming less sensitive to an unchanging
sensory stimulus over time
– Allows you to shift your attention to what is most important at
any given moment
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Process of Sensation
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Process of Sensation
 Signal Detection Theory
– The ability to detect a sensory stimulus (signal) depends on not
only on the intensity of the signal but also on variables such as
distractions and motivation
– Like playing slug bug with your friends
 Distractions (Is your favorite song on the radio?)
 Expectations (Where you have seen a bug parked before?)
 Criterion (How clear must the features be to report spotting of bug?)
– Is there a consequence for reporting false alarms?
– Sonar tracking of Russian naval fleet during cold war (Hunt for
Red October)
– Air traffic controllers, military radar technicians, X-ray technicians
in airports, pregnancy & drug test
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Vision
 Visible spectrum
– The narrow band of electromagnetic waves, 280 –
760 nm in length, that are visible to the human eye
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Vision
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Vision
 Hue
– The property of light commonly referred to as color,
determined primarily by the wavelength of light
reflected from a surface
 Saturation
– The degree to which light waves producing a color
are of the same wavelength; the purity of a color
 Brightness
– The dimension of visual sensation that is dependent
on the intensity of light reflected from a surface and
that corresponds to the amplitude of the light wave
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Vision
 Cornea
– The transparent covering on the front surface of the
eyeball that bends light rays inward through the
pupil
 Lens
– The transparent structure behind the iris that
changes shape as it focuses images on the retina
 Accommodation
– The action of the lens in changing shape as it
focuses objects on the retina, becoming more
spherical for near objects and flatter for far objects
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Vision
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Vision
 Retina
– The layer of tissue at the back of the eye that
contains the rods and the cones and onto which the
incoming image is projected by the lens
– Nearsightedness (myopia)
 When the lens focuses images of distant objects in front of,
rather than on, the retina
– Farsightedness (hyperopia)
 When the focal image is longer than the eye can handle, as
if the image should focus behind the retina
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Vision
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Vision
 Rods
– The light-sensitive receptors in the retina that allow
humans to see in black, white, and shades of gray
in dim light
– Mostly in the periphery
– Take 20 – 30 minutes to fully adapt to darkness
 Cones
– The receptor cells in the retina that enable humans
to see color and fine detail in adequate light, but that
do not function in dim light
– Mostly in the fovea
– Adapt fully to darkness in 2 – 3 minutes
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Vision
 Photopigments (Rhodopsin)
– Enables us to adapt to variations in light
– Two components: opsin and retinal
 Opsin and retinal break apart in light adaptation
 Opsin and retinal bond to one another in dark adaptation
 Bipolar Cells
– Bipolar cells can speed up or slow down the rate of signal
firing
 Ganglion Cells
– Carry signal from bipolar cells to optic nerve
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Vision
Rods & Cones to Bipolar to Ganglion
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Vision
 Fovea
– A small area of the retina that provides the clearest and
sharpest vision because it has the largest concentration of
cones
 Blind spot
– The point where the optic nerve joins the retinal wall
– There can be no rods or cones where the ganglion cells run
through the retinal wall
 Optic nerve
– The nerve that carries visual information from the retina to the
brain
– The two optic nerves come together at the optic chiasm
– Visual fibers from the right half of each retina go to the right
hemisphere, and visual fibers from the left half of each retina
go to the left hemisphere
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Vision
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Vision
 David Hubel and Torsten Wiesel
– Nobel Prize in 1981
– Researched the neurons of the primary visual cortex in the
occipital lobe (1979)
 Primary visual cortex
– The part of the brain in which visual information is processed
in Occipital Lobe
 Lateral Geniculate Nucleus
– Located in the left and right hemispheres of the Thalamus
combine information from both eyes
 Feature detectors
– Neurons in the brain that respond to specific features of a
sensory stimulus
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Vision
 Artificial Vision
– William Dobelle (2000; 2003)
– Artificial visual systems in eight patients who had been blind
provided electrical stimulation to the surface of the visual
cortex
 Color Vision
– Among mammals only primates (humans, apes & monkeys)
are able to perceive a full range of colors.
– Interestingly, fish, birds, reptiles and insects have excellent
color vision and believe it or not dogs may have limited color
vision.
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Vision
 Subtractive Color Mixing
– When paints or pigments are mixed, so that when light falls on
the colored object some wavelengths are absorbed (or
subtracted) and others are reflected.
– Black is the absorption of all wavelengths
– White is the reflection of all wavelengths
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Vision
 Additive Color Mixing
– When lights of different wave lengths simultaneously stimulate
the retina, so that color perception depends on the adding or
combining of these wavelengths.
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Vision
 Trichromatic theory
– First proposed by Thomas Young in 1802 and modified by
Hermann von Helmholtz about 50 years later
– The theory of color vision suggesting that there are three types
of cones, which are maximally sensitive to red, green, or blue,
and that varying levels of activity in these receptors can
produce all of the colors
– George Wald
 Did research that supported the trichromatic theory
 Discovered that even though all cones have basically the
same structure, the retina does indeed contain three kinds
of cones
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Vision
 Trichromatic theory
– Really the wavelengths the receptors are most sensitive to are
blue, green and yellow-green (not red)
 Trichromatic theory does not explain
– Color blindness
– Afterimages
– Color mixing
Three Types of Cones
S-Cones
(Sensitive to blue)
M-Cones
(Sensitive to Green)
L-Cones
(Sensitive to Red)
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Vision
 Opponent-process theory
– First proposed by physiologist Ewald Hering in 1878
and revised in 1957 by researchers Leo Hurvich and
Dorothea Jameson
– The theory that three classes of cells increase their
firing rate to signal one color and decrease their
firing rate to signal the opposing color (red/green,
yellow/blue, white/black)
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Vision
 Afterimage
– The visual sensation that remains after a stimulus is
withdrawn
– After you have stared at one color in an opponentprocess pair (red/green, yellow/blue, black/white),
the cell responding to that color tires and the
opponent cell begins to fire, producing the
afterimage
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Vision
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Vision
 Color blindness
– The inability to distinguish some or all colors,
resulting from a defect in the cones
– About 8% of males experience some kind of
difficulty in distinguishing colors while fewer than
0.5% of females suffer from color blindness
– Two main types:
 red/green (most common type)
 blue/yellow
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Color Blindness
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Audition
 Audition
– The sensation of hearing; the process of hearing
 Robert Boyle
– Demonstrated that sound requires a medium through
which to move, such as air, water, or a solid object
 Frequency
– Measured in the unit called the hertz, the number of
sound waves or cycles per second, determining the
pitch of the sound
– The human ear can hear sound frequencies from low
bass tones of around 20 Hz to high-pitched sounds of
about 20,000 Hz
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Audition
 Amplitude
– Measured in decibels, the magnitude or intensity of
a sound wave, determining the loudness of the
sound; the amplitude of a light wave affects the
brightness of a visual stimulus
– The measuring unit used, bel, is named after
Alexander Graham Bell
 Decibel
– A unit of measurement of the intensity or loudness
of sound based on the amplitude of the sound wave
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Audition
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Audition
 Timbre
– The distinctive quality of a sound that distinguishes
it from other sounds of the same pitch and loudness
– Human voices vary in timbre, providing us with a
way of recognizing individuals when we can’t see
their faces
– Timbres also vary from one instrument to another
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Audition
 Outer ear
– The visible part of the ear, consisting of the pinna
and the auditory canal
– The pinna is the oddly shaped, curved flap of
cartilage that is the visible part of the outer ear
– The auditory canal is about 1 inch long, and its
entrance is lined with hairs
– The eardrum is at the end of the auditory canal and
is a thin and flexible membrane about 1/3 inch in
diameter
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Audition
 Middle ear
– The portion of the ear containing the ossicles, which
connect the eardrum to the oval window and amplify
the vibrations as they travel to the inner ear
– Ossicles
 Named the hammer, the anvil, and the stirrup
 Link the eardrum to the oval window
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Audition
 Inner ear
– The innermost portion of the ear, containing the cochlea, the
vestibular sacs, and the semicircular canals
– Cochlea
 The snail-shaped, fluid-filled chamber in the inner ear that
contains the hair cells (the sound receptors)
 Hair cells
– Sensory receptors for hearing, found in the cochlea
– Basilar Membrane
 Vibrates in response to pressure waves causing auditory hair
cells on the adjoining Organ of Corti
– Organ of Corti
 releases neurotransmitters that activate neurons on the auditory
nerve
 Point of transduction for audition
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Audition
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Audition
 Place theory
– The theory that sounds of different frequency or pitch cause
maximum activation of hair cells at certain locations along the basilar
membrane
– Works best with high frequency tones
– Georg von Békésy (Nobel Prize, 1961) discovered that different
regions (places) on the basilar membrane responded to different
tones by cutting tiny holes in various locations along the cochlea of
guinea pigs
 Frequency theory
– The theory that hair cell receptors vibrate the same number of times
as the sounds that reach them, thereby accounting for how variations
in pitch are transmitted to the brain
– In the 20 to 4,000 Hz. Range the fibers in the auditory nerve actually
do fire in rhythm with the wave frequencies of tones (Rose et.al.,
1967)
– Works best with low frequency tones
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Audition
 Conduction deafness
– Usually caused by disease or injury to the eardrum
or the bones of the middle ear, which prevents
sound waves from being conducted to the cochlea
– Sometimes due to infection or to build up of ear wax
 Sensorineural hearing loss
– Damage to either the cochlea or the auditory nerve
– Presbycusis is the loss of hearing to high
frequencies in part due to less blood flow to the
inner ear which destroys some of the critical neural
elements in this structure.
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Gustation and Olfaction
 Gustation
– The sensation of taste
 Five basic tastes
–
–
–
–
–
Sweet
Sour
Salty
Bitter
Umami (not in text)
 Triggered by the substance glutamate
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Gustation and Olfaction
 Papillae
– The small bumps on your tongue
– Four different types
– Three of them contain taste buds
 Taste buds
– Structures composed of 60 to 100 sensory
receptors for taste
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Gustation and Olfaction
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Gustation and Olfaction
 Three groups of taste sensitivity for sweet and
bitter substances
– Nontasters
 Are unable to taste some sweet and bitter compounds, but
do taste most other substances
– Normal tasters
 Average sense of taste to sweet and bitter compounds
– Supertasters
 Taste certain sweet and bitter compounds with far stronger
intensity than other people
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Gustation and Olfaction
 Olfaction (smell)
– The sensation of smell; the process of smelling
– You cannot smell a substance unless some of its
molecules vaporize
 Olfactory epithelium
– Two 1-square-inch patches of tissue, one at the top
of each nasal cavity, which together contain about
10 million olfactory neurons, the receptors for smell
 Olfactory bulbs
– Two matchstick-sized structures above the nasal
cavities, where smell sensations first register in the
brain
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Gustation and Olfaction
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Gustation and Olfaction
 Pheromones
– Chemicals excreted by humans and other animals
that act as signals to, and elicit certain patterns of,
behavior from members of the same species
– Used by animals to mark off territories and to signal
sexual receptivity
 Karl Grammer
– Suggested that humans, although not consciously
aware of it, respond to pheromones when it comes
to mating
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Skin Senses
 Skin
– The largest organ of your body
– Performs many important biological functions while
also providing much of what is known as sensual
pleasure
 Tactile
– Pertaining to the sense of touch
– Information that is conveyed to the brain when an
object touches and depresses the skin, stimulating
one or more of the several distinct types of
receptors found in the nerve endings
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Skin Senses
 Skin
– Pressure
 Displacement of skin
 Too much pressure will signal pain
– Temperature
 Paradoxical cold is the perception of cold (briefly) when you stick your
hand under hot water. Cold is closer to skin surface and thus gets
stimulated first.
 Menthol produces a cold sensation by stimulating cold receptors
 Methyl Salicylate (Ben Gay) increases peripheral blood flow thus causing
a warm sensation (Shiffman, 2000)
– Pain
 Free-nerve endings respond to pain (rubbing interfers with pain)
 Chemicals that may carry pain: prostaglandins, bradykinins & substance P
 Motivates us to tend to injuries, to restrict activity, and to seek medical
help
 Teaches us to avoid pain-producing circumstances in the future
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Skin Senses
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Skin Senses
 Chronic pain
– Pain that persists for three months or more
– Three common types
 Low-back
 Headache
 Arthritis
– One-third of American adults suffer from chronic
pain
– Chronic pain insensitivity
 Do not have sensitivity to pain at all
 Very rare
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Skin Senses
 Melzack and Wall
– Gate-control theory
 Contend that there is an area in the spinal cord that can act
like a “gate” and either inhibit pain messages or transmit
them to the brain
 You feel pain when pain messages carried by the small,
slow-conducting nerve fibers reach the gate and cause it to
open
 Contend that messages from the brain to the spinal cord can
inhibit the transmission of pain messages at the spinal gate
and thereby affect the perception of pain
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Skin Senses
 Sullivan and others
– Found that people suffered most from pain when
they harbored negative thoughts about it, feared its
potential threat to their well-being, and expressed
feelings of helplessness
 Zborowski
– Compared the responses to pain of Italian, Jewish,
Irish, and native-born Anglo-Saxon patients in a
large hospital in New York
– Among the four groups, Jewish and Italian patients
responded more emotionally and showed
heightened expressions of pain
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Skin Senses
 Substance P
– A peptide neurotransmitter that signals pain from peripheral
nerve fibers to the spinal cord.
 Endorphins
– Chemicals, produced naturally by the pituitary gland, that
reduce pain and positively affect mood
– Some people release endorphins even when they only think
they are receiving pain medication but are given, instead, a
placebo in the form of a sugar pill or an injection of saline
solution
 Periaqueductal Gray Area (PGA)
– Controls pain signals sent to higher brain centers and receives
signals from endorphin neurons for pain analgesia (GABA &
Endorphins). Area also signals descending neurons to the
original sensory neuron synapse in the spinal cord inhibiting
the afferent neurons ability to signal pain (Serotonin).
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Spatial Orientation Senses
 Kinesthetic sense
– The sense providing information about relative
position and movement of body parts
– Gives the position of body parts in relation to each
other and the movement of the entire body and/or
its parts
 Vestibular sense
– The sense that provides information about the
body’s movement and orientation in space through
sensory receptors in the semicircular canals and the
vestibular sacs, which detect changes in the
movement and orientation of the head
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Spatial Orientation Senses
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Perception
 Gestalt principles of perceptual organization
– Figure-ground
 As you view your world, some object seems to stand out from the
background
– Similarity
 Objects that have similar characteristics are perceived as a unit
– Proximity
 Objects that are close together in space or time are usually
perceived as belonging together because of a principle of
grouping called proximity
– Continuity
 We tend to perceive figures or objects as belonging together if
they appear to form a continuous pattern
– Closure
 We perceive figures with gaps in them to be complete
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Perception
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Perception
 You can see a white vase as figure against a
black background, or two black faces in profile
on a white background
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Perception
 Perceptual constancy
– The tendency to perceive objects as maintaining
stable properties, such as size, shape, brightness,
and color, despite differences in distance, viewing
angle, and lighting
– Brightness Color constancy
 Perceiving objects as being the same color even when
variations in color are present
– Size constancy
 Perceiving objects as being about the same size when they
move farther away
– Shape constancy
 Perceiving objects as having a stable or unchanging shape
regardless of changes in the retinal image resulting from
differences in viewing angle
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Perception
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Perception
 Depth perception
– The ability to see in three dimensions and to estimate distance
 Binocular Cues
– Retinal Disparity
– Retinal Convergence
 Monocular Cues
–
–
–
–
–
–
Linear Perspective
Relative Size
Interposition
Texture Gradients
Atmospheric Perspective
Motion Parallax
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Perception
 Binocular depth cues
Depth cues that depend on two eyes
working together
– Retinal Convergence
 Occurs when the eyes turn inward
to focus on nearby objects – the
closer the object, the greater the
convergence
– Binocular disparity (or retinal
disparity)
 Difference between the two retinal
images formed by the eyes’ slightly
different views of the objects
focused on
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Perception
 Monocular depth cues
– Depth cues that can be perceived by only one eye
– Types of cues
 Interposition (Overlap)
– When one object partly blocks your view of another,
you perceive the partially blocked object as farther
away
 Linear perspective
– Parallel lines that are known to be the same distance
apart appear to grow closer together, or converge, as
they recede into the distance
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Perception
 Monocular depth cues (continued)
– Types of cues (continued)
 Relative size
– Larger objects are perceived as being closer to the
viewer, and smaller objects as being farther away
 Texture gradient
– Near objects appear to have sharply defined textures,
while similar objects appear progressively smoother
and fuzzier as they recede into the distance
 Atmospheric perspective
– Objects in the distance have a bluish tint and appear
more blurred than objects close at hand
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Perception
 Monocular depth cues (continued)
– Types of cues (continued)
 Motion parallax
– When you ride in a moving vehicle and look out the
side window, the objects you see outside appear to be
moving in the opposite direction
– Objects seem to be moving at different speeds – those
closest to you appear to be moving faster than those in
the distance
– Objects very far away, such as the moon and the sun,
appear to move in the same direction as the viewer
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Perception
 Direct Perception
– James Gibson
 Pointed out that our perceptions of motion appear to be
based on fundamental, but frequently changing,
assumptions about stability between past experience
(memory) and current cognitive processing
 Our brains search for some stimulus in the environment to
serve as the assumed reference point for stability
 When you’re driving a car, you sense the car to be in
motion relative to the outside environment
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Perception
 Apparent motion
– Phi phenomenon
 An apparent motion illusion occurring when two or more
stationary lights are flashed on and off in sequence, giving
the impression that one light is actually moving from one
spot to the next
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Perception
 Ambiguous figures
– Can be seen in different ways to make different
images
– Best known ambiguous figure is “Old Woman/Young
Woman,” by E. G. Boring
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What do you see?
Now what do you see?
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Copyright
Textbook©Publishing
Allyn & Bacon
20072005
Perception
 Impossible figures
– Do not seem unusual at first
– Figures that cannot be built
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Perception
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Perception
 Illusion
– A false perception of actual stimuli involving a
misperception of size, shape, or the relationship of
one element to another
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Perception
 Müller-Lyer Illusion
– The two lines above are the same length, but the diagonals
extending outward from both ends of the lower line make it look
longer than the upper line
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Perception
 R. L. Gregory
– Believed that susceptibility to the Müller-Lyer and
other such illusions is not innate
– Believed that the culture in which people live is
responsible to some extent for the illusions they
perceive
 Segall and others
– Tested 1,848 adults and children from 15 different
cultures to see if susceptibility to illusions is due to
experience
– Study revealed that experience was a factor
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Perception
 Stewart
– Did a study to see if race offered an explanation for
the cultural differences in observing illusions
– No significant differences were found in
susceptibility to the illusions based on race
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Perception
 Pedersen and Wheeler
– Studied Native American responses to the MüllerLyer illusion among two groups of Navajos
– The group who lived in rectangular houses and had
experienced corners, angles, and edges tended to
see the illusion
– The other group tended not to see it because their
cultural experience consisted of round houses
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Influences on Perception
 Bottom-up processing
– Information processing in which individual
components or bits of data are combined until a
complete perception is formed
 Top-down processing
– Application of previous experience and conceptual
knowledge to recognize the whole of a perception
and thus easily identify the simpler elements of that
whole
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Influences on Perception
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Influences on Perception
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Influences on Perception
 Perceptual set
– An expectation of what will be perceived, which can
affect what actually is perceived
 David Rosenhan
– David Rosenhan and some of his colleagues were
admitted as patients to various mental hospitals with
“diagnoses” of schizophrenia
– Once inside, they acted normal but the staff
members only saw what they expected to see and
not what was actually occurring
– The real patients were the first to realize that the
psychologists were not really mentally ill
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Basketball Game
Instructions: Count the number of times
someone in a white shirt catches the basketball.
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Influences on Perception
 Inattentional blindness
– The phenomenon in which we miss an object in our
field of vision because we are attending to another
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Influences on Perception
 Simons and his colleagues
– Showed participants a videotape of a basketball
game in which one team is uniformed in white and
the other in black
– Instructed them to count how many times the ball
was passed from one player to another either on the
white or black team
– About a third of participants typically fail to later
recall the presence on the screen of even extremely
incongruent stimuli (e.g., a man dressed in a gorilla
costume) under such conditions
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Influences on Perception
 David Strayer and his colleagues
– Studies showed that drivers often failed to perceive
vehicles braking directly in front of them while
engaged in hands-free cell phone conversations
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Influences on Perception
 James Haxby
– Suggests that there is a “core system” of face
perception that uses the universal features of the
human face to make judgments about people’s
identities
– Cross-modal perception
– The way we combine information from two sensory
modalities
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Influences on Perception
 Social perception
– Facial expressions, the visual cues for emotional
perception, often take priority over the auditory cues
associated with a person’s speech intonation and
volume, as well as the actual words spoken
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