Sensation and Perception

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Chapter 4

• Sensation and Perception

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Sensation and Perception

• Chemical senses
• Smell
• Taste
• Skin senses
• Touch
• Pressure
• Temperature
• Kinesthesis Vestibular senses
• ESP

• Life Connections Pain
• Methods for coping with pain

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Sensation and Perception

• Sensation
• is the stimulation of sensory receptors and the
  transmission of sensory information to the
  central nervous system.
• Perception
• is an active process in which sensations are
  organized and interpreted to form an inner
  representation of the world.
• Five Senses
• Vision.
• Hearing.
• Smell.
• Taste.
• Touch.

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Thresholds

• Absolute threshold refers to the weakest amount
  of a stimulus that a person can distinguish from
  no stimulus at all 50 of the time.
• Examples include
• Vision candle flame viewed from about 30 miles
  on a clear, dark night.
• Hearing a watch ticking from about 20 feet away
  in a quiet room.
• Difference Threshold the minimum difference in
  magnitude of two stimuli required to tell them
  apart 50 of the time (just noticeable
  difference).

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Signal-Detection Theory

• Considers the human aspects of sensation, and
  perception
• Assumes that the relationship between a physical
  stimulus and a sensory response is not just
  mechanical.
• Other factors include
• Training (learning).
• Motivation (desire to perceive).
• Psychological states such as fatigue or
  alertness.

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Sensory Adaptation

• the sensory process of adjustment.
• Positive adaptation
• Becoming more sensitive to stimulation.
• Negative adaptation
• Becoming less sensitive to stimulation.

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Vision

• More than half of our brains cerebral cortex is
  devoted to visual functions.

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The Eye

• Light first passes through the transparent
  cornea.
• The amount of light that is allowed to enter is
  controlled by the muscle called the iris (the
  colored part of the eye).
• The actual opening in the iris is called the
  pupil.
• The lens adjusts or accommodates to the image by
  changing its thickness. The thickness permits a
  clear image of the object to be projected onto
  the retina.

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Figure 4.2 The Human Eye. In both the eye and a
camera, light enters through a narrow opening and
is projected onto a sensitive surface. In the
eye, the photosensitive surface is called the
retina, and information concerning the changing
images on the retina is transmitted to the brain.
The retina contains photoreceptors called rods
and cones. Rods and cones transmit sensory input
back through the bipolar neurons to the ganglion
neurons. The axons of the ganglion neurons form
the optic nerve, which transmits sensory
stimulation through the brain to the visual
cortex of the occipital lobe.
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The Eye

• Rods and Cones
• Cones are most densely packed in a small spot at
  the center of the retina called the fovea.
• Visual acuity (sharpness and detail) is greatest
  at this spot.
• Rods are most dense toward the periphery of the
  retina.
• Rods allow us to see in black and white.
• Cones provide color vision.
• In contrast to visual acuity is the blind spot
  which is the part of the optic nerve which leaves
  the eye.

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Light Adaptation

• Dark adaptation
• the process of adjusting to lower lighting
  conditions.
• Light adaptation
• Adapting to brighter lighting takes place much
  more rapidly.

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Figure 4.5 Dark Adaptation. This illustration
shows the amount of light necessary for detection
as a function of the amount of time spent in the
dark. Cones and rods adapt at different rates.
Cones, which permit perception of color, reach
maximum dark adaptation in about ten minutes.
Rods, which permit perception of dark and light
only, are more sensitive than cones. Rods
continue to adapt for up to about 45 minutes.
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Color Vision Two theories

• Trichromatic Theory.
• Helmholtz suggested that the retina in the eye
  must have three different types of color
  photoreceptors or cones.
• Is theory works well to explain color blindness.
• Opponent-Process theory.
• Hering proposed that there are three types of
  color receptors but they dont respond just to
  red, green and blue-violet.
• They are pairs including red-green blue-yellow
  and a type that perceives differences in
  brightness.
• These pairs of receptors are what make
  afterimages possible.

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Color Blindness

• If you can discriminate among the colors of the
  visible spectrum, you have normal color vision
  and are labeled a trichromat.
• People who are totally color blind are called
  monochromats.
• Partially color-blind people are called
  dichromats as they can discriminate only among
  two colors-red and green or blue and yellow-and
  the colors derived from mixing these colors.
• Partial color blindness is a sex-linked trait
  that affects mostly males.

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Figure 4.10 Plates from a Test for Color
Blindness. Can you see the numbers in these
plates from a test for color blindness? A person
with redgreen color blindness would not be able
to see the 6, and a person with blueyellow color
blindness would probably not discern the 12.
(Caution These reproductions cannot be used for
actual testing of color blindness.)
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Color Vision

• Afterimages.
• Persistent sensations of color are followed by
  perception of the complimentary color when the
  first color is removed.

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Figure 4.9 Three Cheers for theGreen, Black,
and Yellow. Dont be concerned. We can readily
restore Old Glory to its familiar hues. Place a
sheet of white paper beneath the book and stare
at the black dot in the center of the flag for at
least 30 seconds. Then remove the book. The
afterimage on the paper beneath will look
familiar.
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CONTROVERSY IN PSYCHOLOGY When Light With
Different Wavelengths Stimulate The Retina

• Research suggests that each theory of color
  vision is partially correct.
• The cones may be as Helmholtz claimed.
• The transmission of the signals to the brain are
  as Hering proposed.

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Visual Perception

• Visual perception
• is the process by which we organize or make sense
  of the sensory impressions caused by the light
  that strikes our eyes.
• involves our knowledge, expectations, and
  motivations.
• is an active process through which we interpret
  the world around us.
• Gestalt psychologists refer to closure as being
• the integration of disconnected pieces of
  information into a meaningful whole, or
• the tendency to perceive a complete or whole
  figure even when there are gaps in the sensory
  input.

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Figure 4.11 Closure. Meaningless splotches of
ink or a horse and rider? This figure illustrates
the Gestalt principle of closure.
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Perceptual Organization

• Gestalt psychologists are interested in the way
  we integrate bits and pieces of sensory
  stimulation into meaningful wholes.
• Figure-Ground Perception.
• When figure-ground relationships are ambiguous,
  or capable of being interpreted in various ways,
  our perceptions tend to be unstable, shifting
  back and forth.

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• Figure 4.13 The Rubin Vase. A favorite drawing
  used by psychologists to demonstrate
  figureground perception. Part A is ambiguous,
  with neither the vase nor the profiles clearly
  the figure or the ground. In part B, the vase is
  the figure in part C, the profiles are.

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Figure 4.14 Necker Cube. Ambiguity in the
drawing of the cube makes perceptual shifts
possible. Therefore, the darker tinted surface
can become either the front or back of the cube.
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Perceptual Organization

• Other Gestalt Rules for Organization
• Proximity
• nearness.
• Similarity
• we perceive similar objects as belonging
  together.
• Continuity
• we perceive a series of points or a broken line
  as having unity.
• Common Fate
• elements seen as moving together are perceived as
  belonging together.

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Figure 4.15 Some Gestalt Laws of Perceptual
Organization. These drawings illustrate the
Gestalt laws of proximity, similarity,
continuity, and closure.
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Perceptual Organization

• Top-Down Versus Bottom-Up Processing.
• Top-Down Processing
• Use the larger pattern to guide subordinate
  tasks.
• Bottom-Up processing
• Begin with bits and pieces of information and
  become aware of the pattern formed only after
  youve worked on it a while.

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Perception of Motion

• Visual perception of movement is based on change
  of position relative to other objects.
• Types of apparent movement (illusions of
  movement).
• The Autokinetic Effect
• is the tendency to perceive a stationary point of
  light as moving in a dark room.
• Stoboscopic Motion
• is what makes motion pictures possible.
• The illusion of movement is provided by the
  presentation of a rapid progression of images of
  stationary objects.
• The Phi Phenomenon
• occurs as the on-off process of lights is
  perceived as movement.
• We tend to perceive a series of points as having
  unity, so each series of lights is perceived as a
  moving line.

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Depth Perception

• Monocular Cues cues that can be perceived by one
  eye.
• Perspective
• distances between far off objects appear to be
  smaller than equivalent distances between nearby
  objects.
• Relative size
• the fact that distant objects look smaller than
  nearby objects of the same size.
• Clearness of an object
• We sense more details of nearby objects.
• Interposition
• Nearby objects can block our view of more distant
  objects.
• Interposition is placing of one object in front
  of another.

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Figure 4.17 The Effects of Interposition. The
four circles are all the same size. Which circles
seem closer? The complete circles or the circles
with chunks bitten out of them?
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Depth Perception

• Monocular Cues continued.
• Shadows
• opaque objects block light and produce shadows
  giving us a relationship to the source of light.
• Texture Gradient
• close objects are perceived as having rougher
  textures.

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Figure 4.18 Shadowing as a Cue for Depth.
Shadowing makes the circle on the right look
three-dimensional.
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Depth Perception

• Binocular Cues cues that can be perceived by
  both eyes.
• Retinal disparity
• The difference between projected images (e.g.
  different angles).
• Closer objects have greater retinal disparity.
• Convergence
• Causes feelings of tension in the eye muscles and
  provides another binocular cue for depth.

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Perceptual Constancies

• Size constancy
• Allows us to perceive objects to be the same size
  even when viewed from different distances.
• Experiences teach us about perspective.
• Color constancy
• The tendency to perceive objects as retaining
  their color even though lighting conditions may
  alter their appearance.
• Brightness constancy
• similar to color constancy.
• Shape constancy
• The tendency to perceive objects as maintaining
  their shape, even if we look at them from
  different angles so that the shape of their image
  on the retina changes dramatically.

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Figure 4.19 Brightness Constancy. The orange
squares within the blue squares are the same hue,
yet the orange within the dark blue square is
perceived as brighter. Why?
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Figure 4.20 Shape Constancy. When closed, this
door is a rectangle. When open, the retinal image
is trapezoidal. But because of shape constancy,
we still perceive it as rectangular.
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FEATURES A CLOSER LOOK Visual Illusions Is
Seeing Believing?

• The Hering-Helmholtz and Muller-Lyer illusions
  work because of our life experience.
• Lifelong use of perceptual cues.
• Experience with perspectives.
• The Ponzo illusions seems to work because of size
  constancy.

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Figure 4.21 The HeringHelmholtz and MüllerLyer
Illusions. In the HeringHelmholtz illusion, are
the horizontal lines straight or curved? In the
MüllerLyer illusion, are the vertical lines
equal in length?
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• Figure 4.22 A Monstrous Illusion. The two
  monsters in this drawing are exactly the same
  height and width. Yet the top one appears to be
  much larger. Can you use the principle of size
  constancy to explain why?

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Hearing The Ear

• The ear has three parts the outer ear, middle
  ear, and the inner ear.
• The outer ear is shaped to funnel sound waves to
  the eardrum.
• The eardrum is a thin membrane that vibrates in
  response to sound waves and thereby transmits
  them to the middle and inner ears.

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Figure 4.26 The Human Ear. The outer ear funnels
sound to the eardrum. Inside the eardrum,
vibrations of the hammer, anvil, and stirrup
transmit sound to the inner ear. Vibrations in
the cochlea transmit the sound to the auditory
nerve by way of the basilar membrane and the
organ of Corti.
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The Ear

• The middle ear functions as an amplifier.
• The stirrup is attached to another vibrating
  membrane (the oval window) which transmits
  vibrations to the cochlea.
• The cochlea is a snail shaped structure that
  contains membranes.
• One of these membranes is the basilar membrane.
• Attached to the basilar membrane is the command
  post of hearing (organ of Corti).
• Here there are receptor cells called hair cells.
  
• Hair cells dance in response to basilar membrane
  vibrations.
• Their movements generate neural impulses which
  are sent to the brain via the auditory nerve.
• Auditory input is then projected onto the hearing
  areas of the temporal lobes of the cerebral cortex

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Locating Sounds

• A sound that is louder in the right ear is
  perceived as coming from the right.
• It is difficult to determine if the sound is
  directly in front of or behind you.
• Both loudness and the sequence in which the
  sounds reach the ears provide directional cues.

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Deafness

• More than 1 in 10 Americans has a hearing
  impairment, and 1 in 100 cannot hear at all.
• Two major types of deafness are conductive and
  sensorineural deafness.
• Conductive deafness
• stems from damage to the structures of the middle
  ear.
• This is the hearing impairment often found among
  older people.
• Sensorineural deafness
• stems from damage to the structures of the inner
  ear, most often the loss of hair cells, which
  normally do not regenerate.
• Acoustic trauma
• prolonged exposure to very loud noises.
• The ringing sensation that often follows exposure
  to loud noises probably means that hair cells
  have been damaged.

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The Chemical Senses

• Smell
• If you did not have a sense of smell, an onion
  and an apple would taste the same to you.
• Odors are detected by sites on receptor neurons
  in the olfactory membrane high in each nostril.
• The sense of smell adapts rapidly to odors such
  that we lose awareness of them.
• Our sense of smell declines when we age gt food
  doesnt taste as good

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The Chemical Senses

• Taste
• Four primary taste qualities sweet, sour,
  salty, and bitter.
• Food flavor depends on its odor, texture,
  temperature as well as taste.
• Taste cells are receptor neurons located on taste
  buds.
• Humans have approximately 10,000 taste buds most
  of which are located on the edge and back of your
  tongue.
• Taste cells reproduce rapidly enough to renew
  themselves weekly

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The Skin Senses

• The skin senses include touch, pressure, warmth,
  cold, and pain.
• Touch and Pressure
• information concerning not only touch, but also
  pressure, temperature, and feedback from the
  muscles involved in movements of our hands.
• The sense of pressure, like the sense of touch
  undergoes rapid adaptation.
• Temperature
• The receptors for temperature are neurons located
  just beneath the skin.
• Sensations of temperature are relative to skin
  temperature.

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Kinesthesis and the Vestibular Sense

• Kinesthesis
• the sense that informs you about the position and
  motion of parts of the body.
• Sensory information is fed back to the brain from
  sensory organs in the joints, tendons, and
  muscles.
• The Vestibular Sense
• Your vestibular sense tells you whether you are
  upright gt sense of balance
• Sensory organs located in the ears monitor your
  bodys motion and position in relation to
  gravity.
• They tell you if you are falling and if your body
  is changing speed.

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Extrasensory Perception

• Hard research does not support the existence of
  ESP.
• Nonetheless 60 of Americans believe that some
  people have psychic powers or ESP.

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LIFE CONNECTIONS Pain, Pain, Go Away-Dont
Come Again Another Day

• A Gallup survey of 2,002 adults in the U.S.
  showed that 89 experience pain at least once a
  month.
• Pain means that something is wrong in the body.
• Pain is adaptive.
• There are no nerve endings for pain in the brain.
  
• Postaglandins (substance P) facilitate
  transmission of the pain message to the brain and
  heighten circulation to the injured area.
• Other aspects influence pain
• Visual and other sensory inputs tell us what is
  happening and influence the cognitive
  interpretation of the situation.

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Figure 4.28 Perception of Pain. Pain originates
at the point of contact, and the pain message to
the brain is initiated by the release of
prostaglandins, bradykinin, and substance P.
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LIFE CONNECTIONS Pain, Pain, Go Away-Dont
Come Again Another Day.

• Phantom Limb Pain.
• About 2 out of 3 combat veterans with amputated
  limbs report feeling pain in missing or phantom
  limbs.
• Seems to involve activation of nerves in the
  stump of the missing limb.
• Gate Theory.
• The nervous system can process only a limited
  amount of stimulation at a time.
• In a sense, there is competition for the
  attention of neurons.
• Acupuncture.
• Research has shown that acupuncture stimulates
  nerves that reach the hypothalamus and may also
  result in the release of endorphins.

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LIFE CONNECTIONS Pain, Pain, Go Away-Dont
Come Again Another Day

• Modern Psychological Methods for Coping with
  Pain.
• The primary treatment has been chemical
  pain-killing drugs.
• Knowledge of medical procedures reduces stress by
  helping people maintain control over their
  situation.
• Distraction and Fantasy
• Diverting attention from pain helps many cope
  with it.
• Rub the injured area (for small injuries).
• Hypnosis has been used to reduce chronic pain, as
  an anesthetic in dentistry, childbirth, even in
  some forms of surgery.