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					Chapter 8

      Sensation and
Section 1: Sensation

• Sensation and perception are needed to
  gather and interpret information in our
• Any aspect of or change in the environment
  to which an organism responds is called a
  – A sensation occurs anytime a stimulus activates
    one of your receptors.
  – The sense organs detect physical changes in
    energy such as heat, light, sound, and physical
• A sensation may be combined with other
  sensations and your past experience to yield
  a perception.
• Psychologists are interested in the
  relationship between physical stimuli and
  sensory experiences.
  – This study is called psychophysics.
  – The goal is to understand how stimuli from the
    world affect the sensory experiences.
• In order to establish laws about how people
  sense the external world, psychologists first
  try to determine how much of a stimulus is
  necessary for a person to sense it at all. This
  is called the threshold.
   – Absolute threshold: the weakest amount of a
     stimulus required to produce a sensation.
• In humans, the absolute threshold in the five
  senses are:
  – Vision: seeing a candle flame 30 miles away on a
    clear night
  – Hearing: hearing a watch ticking 20 feet away
  – Taste: tasting 1 teaspoon of sugar dissolved in 2
    gallons of water
  – Smell: smelling I drop of perfume in a 3 room
  – Touch: feeling a bee’s wing falling a distance of 1
    centimeter onto your cheek
  ** Humans sense a somewhat limited range of the physical phenomena in the everyday world.
• Weber’s Law: the larger or stronger a
  stimulus, the larger the change required for a
  person to notice that anything has happened.
  – Backpack example
• Senses are most responsive to increases and
  decreases, and to new events rather than to
  ongoing, unchanging stimulation.
  – Movie theater example
Section 2: The Senses

• Vision
  – Is the most studied of all the senses
  – Provides us with a great deal of information about
    our environment
  – It works by:
     • Light entering the eye through the pupil where it reaches
       the lens that focuses the light onto the retina
     • The photoreceptor cells (rods and cones) change the
       light energy into impulses that travel to the brain by way
       of the optic nerve
           – When a person’s cones do not work properly, he/she is
             said to be color-deficient (color blind)
– Binocular vision
   • Because we have two eyes, we see two images that
     combine to produce one complete image (binocular
   • Difference between the images is called retinal disparity
       – Essential for depth perception
           » The greater the difference, the closer the object
• Hearing
  – Depends on the vibrations of the air, called sound
    waves, which passes through various bones until
    they reach the inner ear where hair like cells
    change the sound vibrations into signals that
    travel to the brain through the auditory nerve
  – 2 Types of Deafness
     • Conduction – something hinders the motion through the
       outer or middle ear or when the bones become rigid and
       can not carry sounds – can be helped with hearing aids
     • Sensorineural – damage to the cochlea, hair cells, or the
       auditory neurons – can be helped with cochlear implants
• Smell and Taste
  – Known as chemical senses because they are
    sensitive to chemical molecules
  – Gaseous molecules travel up the nose to the
    receptors that send messages to the brain through
    the olfactory nerve
  – Liquid chemicals stimulate receptors in the taste
    buds, sending information to the brain
     • Four primary sensory experiences are sour, salty, sweet,
       and bitter
  – The combination of taste, smell, and tactile
    sensations is known as flavor
• Touch (skin senses)
  – Receptors in the skin provide the brain with at
    least four kinds of information about the
    environment : pressure, warmth, cold, and pain
  – Gate control theory of pain
     • We can lessen some pains by shifting our attention away
       from the pain impulses or by sending other signals to
       compete with the pain signals
Section 3: Perception

• Perception: brain receives information from
  the senses and organizes & interprets it into
  meaningful experiences
• The brain makes sense of the world by
  creating whole structures out of bits and
  pieces of information – each whole created
  by the brain is called a Gestalt.
– The principles that people use in organizing such
  patterns are:
   • Proximity – group together elements that are close
   • Continuity – see smooth, continuous contours
   • Similarity – group together elements that are similar in
   • Simplicity – perceive a pattern in the simplest form
   • Closure - group according to enclosed or completed
• Perceiving is something that people learn to
• Experiments show that active involvement in
  one’s environment is important for accurate
• Learning to perceive is influenced by our
  needs, beliefs, and expectations.
  – “When we want to see something, we are more
    likely to see it.”
     • Hungry people experiment
• Constancy
   – When we have learned to perceive certain objects
     in our environment, we tend to see them in the
     same way, regardless of changing conditions.
• Illusions
   – Incorrect perceptions created when perceptual
     cues are distorted so that our brains cannot
     correctly interpret space, size, and depth cues.
• Extrasensory perception (ESP)
   – Receiving information about the world through
     channels other than the normal senses
– Four types of ESP
   • 1) clairvoyance – perceiving objects or information
     without sensory input
   • 2) telepathy – reading someone else’s mind or
     transferring one’s thoughts
   • 3) psychokinesis – moving objects through purely mental
   • 4) precognition – ability to foretell events
– Scientists have been investigating ESP since the
– Most people claiming to have ESP have been
  proven to be frauds.

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