Chapter 8- Sensation and Perception

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Chapter 8- Sensation and Perception Powered By Docstoc
 Stimulus- any aspect or change in environment to
  which an organism responds
   Alarm, light, aching muscle
 Sensation- occurs when a stimulus activates a
 Perception- the organization of sensory
  information into meaningful experiences
 How much of a stimulus is necessary for a person to
  sense it?
 Absolute threshold- the weakest amount of a
  stimulus that a person can detect half the time
   Found from completing many trials and averaging them
Human Absolute Thresholds
The Human Senses
Sense         Stimulus         Sense Organ     Receptor          Sensation
Sight         Light waves      Eye             Rods and          Colors, patterns,
                                               cones of retina   textures, motion,
Hearing       Sound waves      Ear             Hair cells in     Noises, tones
                                               the inner ear
Skin          External         Skin            Nerve endings     Touch, pain,
Sensations    contact                          in skin           warmth, cold
Smell         Volatile         Nose            Hair cells of     Odors
              substances                       olfactory
Taste         Soluble          Tongue          Taste buds of     Flavors
              substances                       tongue
Vestibular    Mechanical and   Inner ear       Hair cells of     Spatial mvmt. and
Sense         gravitational                    semicircular      gravitational pull
              forces                           canals

Kinesthesis   Body             Muscles,        Nerve fibers      Movement and
              movement         joints, tendons                   position of body
Sensory Differences and Ratios
 Difference threshold- the smallest change in a
  physical stimulus that can be detected between two
 AKA: Just noticeable difference (JND)-
Sensory Differences and Ratios
  A sensory experience depends more on changes in the
   stimulus than on the absolute size or amount of the
  Weber’s Law- the larger or stronger the stimulus,
   the larger change required for a person to notice
   that anything has happened to it
Sensory Adaptation
 Senses are more responsive to increases and decreases
 and to new events rather than to ongoing stimulation
   Adapting to a dark movie theater, cold water,
    disagreeable odors, street noise
Sensation- Thresholds
 Signal Detection Theory
  predicts how and when we detect the presence of a faint
   stimulus (signal) amid background stimulation (noise)
  assumes that there is no single absolute threshold
  detection depends partly on person’s
       experience
       expectations
       motivation
       level of fatigue
The Stroop Effect
                       Two stimuli are

                       Preattentive processing
                        acts as an interference
 Light enters through the pupil- regulates the amount of
  light coming in
 Light reaches the lens- a flexible structure that changes its
  shapes to focus light on the retina
 Retina- the innermost coating of the back of the eye,
  contains rods and cones, which are responsible for
  transporting light energy into neuronal impulses, which
  travel along the optic nerve to the brain
Finding Your Blind Spot
 Make sure the cross is on the right. Close your
  right eye and look directly on the cross with your
  left eye. Notice that you can also see the dot.
  Focus on the cross, but be aware of the dot as you
 slowly bring the diagram towards your face. Now
 close your left eye and look directly at the dot with
 your right eye. What has happened? When you
 hold the diagram so that the light from the dot
 falls on your blind spot, you cannot see the dot.
 This is your blind spot.
 Cones- require more light than rods before they begin
  to respond, work best in daylight
 Rods- sensitive to lower levels of light, helpful in night
 Many more rods than cones, but cones are sensitive to
 A form of electromagnetic radiation
 Visible light is just a small portion of the electromagnetic
 An object’s color depends on the light that reaches our

Color Deficiency
 Happens when all or some cones do not function
 Most color deficient people will be able to see
  some colors
 Most have problems distinguishing red and
  green, others cannot distinguish between yellow
  and blue. A few are totally color deficient and
  depend only on rods.
 Effects about 8% of men and 1% of women; a
  hereditary condition passed on by women
Visual Information
 Trichromatic (three color) Theory
   Young and Helmholtz
   three different retinal color receptors
         red
         green
         blue
Opponent-Process Theory- opposing
retinal processes enable color vision
Binocular Fusion
 The process of combining the images received from the two
  eyes into a single, fused image
 Retinal disparity- the difference between the images
  stimulating each eye
 Essential to depth perception- a large retinal disparity means
  an object is nearby
Nearsightedness and Farsightedness
 Perfect vision- perfectly shaped eyeballs
 Eyeballs too long- nearsighted (objects are
  focused at a point slightly in front of the retina so
  you can see near objects, but those far away seem
 Eyeballs too short- farsighted (objects are focused
  at a point slightly behind the retina, so you can see
  distant objects clearly, but near objects appear
 Sound passes through various bones until they reach the
  inner ear, which contains cillia that move back and forth.
  These hair cells change sound vibrations into neuronal
  signals that travel through the auditory nerve into the brain.
 Loudness depends on the amplitude (height) of
  sound waves- measured in decibels

 Sounds over 110 decibels can cause damage,
 persistent sounds over 80 decibels can cause
 Pitch: Depends on frequency, or the rate of vibration
 Low frequency- deep sounds
 High frequencies- shrill squeaks
 Sources of sounds are located when ears work together.
  When a noise occurs on the right, it reaches the right ear a
  fraction of a second earlier and is slightly louder in the
  right ear.
 More hearing loss in younger people with the use of iPods and earbud
    headphones that is similar to that found in aging adults.
   Earbuds are placed directly in the ear and can boost the sound signal by
    as much as six to nine decibels. It’s enough to cause hearing loss after
    only about an hour and 15 minutes.
   60 percent/60 minute rule- Using the MP3 devices, including iPods, no
    more than about an hour a day and at levels below 60 percent of
    maximum volume.
   To avoid permanent hearing loss in the middle ranges --the range
    required to hear conversation in a noisy restaurant, for example -- they
    recommend the older style, larger headphones that rest over the ear
   Another option is the use of noise-canceling headphones that
    eliminate background noise so listeners don't have to crank the volume
    so high.
The Pathway of Sound
 Outer ear- receives sound waves, earflap directs sound
  down auditory canal. The auditory canal begins to
  vibrate, which causes the eardrum to vibrate
The Pathway of Sound
 Middle Ear- air-filled cavity with three tiny bones-
  hammer, anvil, and stirrup. Bones vibrate and push
  against the cochlea
Pathway of Sound
 Inner Ear- cochlea, a bony tube that contains fluids and
  neurons. Pressure makes the liquid inside the cochlea
  move and tiny hairs pick up the motion and turn into
  neuronal impulses which are sent to the brain
 Conduction- something hinders motion through the
 outer or middle ear or when the bones in the middle
 ear become rigid and cannot carry sound
   Help from hearing aids- change sound waves into
    vibrations and send to inner ear
 Sensorineural- damage to cochlea or auditory
   Cochlear implants – electronic device in cochlea
 Regulated by the vestibular system-
   Semicircular canals (3)- filled with fluid, hair cells are bent when
    movement occurs
   Stimuli include spinning, falling, tilting
   Overstimulation results in dizziness and motion sickness
Smell and Taste
 Chemical senses- receptors are sensitive to chemical
 Smell- gas molecules enter the nose in vapors, smell
  receptors send messages through the olfactory nerve
 Taste- liquid chemicals stimulate receptors in taste
  buds, info sent to brain along with texture and temp.
 Four primary sense experiences- sour, salty, bitter, and
   Flavor= taste + smell + tactile sensation
   Flavors can be detected anywhere on the tongue
   Supertasters- two or more times the taste buds
   Much of taste actually is smell
   Sensations of warmth and cold
    also effect taste
Skin Senses: Touch
 Skin receptors provide info about pressure, warmth,
 cold, and pain
   Varies from place to place
   Protection
   Varying sensitivity to temperature
   Pain makes it possible to prevent damage
Pain Perceptions
 Can be sharp and localized or dull and generalized

 Gate control theory of pain- lessen pain
 by shifting attention away from pain
 impulses or sending other signals to
 compete with pain signals
Body Senses
 Kinesthesis- sense of body movement and position
   Sensation from receptors in the muscles, tendons, and
   Movements would be jerky and uncoordinated without
 The brain receives information from the
 senses and unconsciously organizes into
 meaningful experiences
 Makes whole structures out of bits and pieces of info in
  the environment
 Gestalt- this meaningful whole (German for pattern)
Gestalt Grouping Principle 1
 How are perceptions constructed?
 Similarity:
   occurs when objects look similar to one
    another. People often perceive them as a
    group or pattern.
Gestalt Grouping Principle 2
 How are perceptions constructed?

 Continuation:
   occurs when the eye is compelled to move
    through one object and continue to
    another object.
Gestalt Grouping Principle 3
 How are perceptions constructed?
 Proximity:
   occurs when elements are placed close
    together. They tend to be perceived as a
Gestalt Grouping Principle 4
 How are perceptions constructed?
 Simplicity:
   we see the simplest shapes possible
Gestalt Grouping Principle 5
 How are perceptions constructed?
 Closure:
   occurs when an object is incomplete or a
    space is not completely enclosed. If enough
    of the shape is indicated, people perceive
    the whole by filling in the missing
Figure Ground Perception:
 The ability to discriminate properly between
 a figure and its background
Perceptual Inference:
 Filling in the gaps in what our senses tell us
   Assuming the sound of barking is a dog
   Assuming a chair will hold us even in a
    dark theater
   Depends on experience
Learning to Perceive
 In large part, something we learn to do
   Infants under one month will smile at a nodding image
    the size of a human face
   At about 20 weeks, a blank oval will not, but a mask will
   At 30 weeks, will smile more readily at a familiar face
   Will not be able to recognize different people until 7 or 8
 Learning to perceive is influenced by environment
 interaction, needs, beliefs, and experiences
 It was a dark and misty night as Sandy ran across
  campus. A street light cast a shadow of another
  person close behind. With heart pounding, Sandy
  accelerated away from the pursuer and headed for
  the dorm.
 Tell me:
   Something about the characters
   What happens next
   How the story ends
Subliminal visual messages present below the
 Brief auditory or
 absolute threshold so that there is a less than 50%
 chance that they will be perceived
   False claim that the words “Eat popcorn” and “Drink Coke”
    had flashed briefly on a movie screen once every 4 seconds
    for 1/3000 of a second and that sales had risen
   Hysterical reaction- Congress called for FCC, admitted
    data was false. But still banned in 1974, regardless of
 Even if it is possible for people to perceive info at low
  levels of intensity, no clear evidence that they
  influence people. But many believe it is a powerful
  advertising tool
Depth Perception:
 The ability to
 recognize distances
 and three
   Present in infancy
   Testing infants 6-14
   months: most have depth
Visual Cliff
 The Visual Cliff is a test given to infants to see if they have
    developed depth perception.
   Then, a piece of glass or other clear material is placed on
    top of the platform and extends well off of the platform,
    creating a sort of bridge.
   An infant is then placed on the platform, and the infant's
    mother stands on the other side of the clear bridge.
   The mother calls for the child who, if it crawls off the
    platform and onto the clear bridge, it does not yet have
    depth perception.
   If it stops when it gets to the edge of the platform, looks
    down, and either is reluctant to cross or refuses to cross,
    then the child has depth perception.
 Monocular Depth Cues:

 Perceive distance and depth with a single eye
   Size (bigger = nearer)
   Relative height (objects that appear farther
    away are higher on your plane of view)
   Interposition (closer objects block distant
   Light and shadows (brighter appear closer)
   Texture density (more detail appear closer)
Monocular Depth Clues:
 Motion Parallax- the apparent movement
  of objects when you move from side to side
  or walk around; Near objects seem to move
 Linear Perspective- parallel lines will
  converge in the distance
 Relative motion- objects nearby are
  moving in the opposite direction objects far
  away are moving in the same direction
Binocular Depth Cues:
 Convergence- turning eyes inward to look
  at near objects
 Retinal Disparity- large = close
 The tendency to perceive certain objects in
 the same way regardless of changing angle,
 distance, or lighting
 Perceptions that misrepresent physical stimuli; cues
 are distorted
   Converging lines = distance
Extrasensory Perception
 An ability to gain information by some other means
  other than the ordinary senses
 Clairvoyance- perceiving objects or information
 Telepathy- reading someone's mind or transferring
 Psychokinesis- moving objects through purely mental
 Precognition- ability to foretell events
Extrasensory Perception
 James Randi has campaigned against people who say
  they have ESP
 Many are convinced because of an intense personal
  experience that cannot be scientifically validated
   Successes and failures must be taken into account
 Findings are unstable and contradictory

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