Sensations and Perceptions

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					Sensations and Perceptions
  Sensations and Perceptions
• Sensations can be defined as the passive
  process of bringing information from
  the outside world into the body and to
  the brain. The process is passive in the
  sense that we do not have to be
  consciously engaging in a "sensing"
Sensations and Perceptions
  Sensations and Perceptions
• Perception can be defined as the active
  process of selecting, organizing, and
  interpreting the information brought to
  the brain by the senses.
Sensations and Perceptions
• 1) Sensation occurs:
• a) Sensory organs absorb energy from a
  physical stimulus in the environment.
• b) Sensory receptors convert this energy
  into neural impulses and send them to the
    How They Work Together
• 2) Perception follows:
• a) The brain organizes the information and
  translates it into something meaningful.
How They Work Together
         Selective Attention
• 1) Selective Attention - process of
  discriminating between what is important &
  is irrelevant (Seems redundant: selective-
  attention?), and is influenced by
      Perceptual Expectancy
• 2) Perceptual Expectancy - how we
  perceive the world is a function of our past
  experiences, culture, and biological
Perceptual Expectancy
• Psychophysics can be defined as, the
  study of how physical stimuli are
  translated into psychological
• In order to measure these events,
  psychologists use.
• 1) Threshold - a dividing line between what has
  detectable energy and what does not.
• For example - many classrooms have automatic
  light sensors. When people have not been in a
  room for a while, the lights go out. However,
  once someone walks into the room, the lights go
  back on. For this to happen, the sensor has a
  threshold for motion that must be crossed before
  it turns the lights back on. So, dust floating in the
  room should not make the lights go on, but a
  person walking in should.
• 2) Difference Threshold - the minimum amount
  of stimulus intensity change needed to produce
  a noticeable change.
• The greater the intensity (ex., weight) of a
  stimulus, the greater the change needed to
  produce a noticeable change.
• For example, when you pick up a 5 lb weight,
  and then a 10 pound weight, you can feel a big
  difference between the two. However, when you
  pick up 100 lbs, and then 105 lbs, it is much
  more difficult to feel the difference.
      Signal-Detection Theory
• 3) Signal-Detection Theory - detection of a
  stimulus involves some decision making process
  as well as a sensory process. Additionally, both
  sensory and decision making processes are
  influenced by many more factors than just
• a) Noise - how much outside interference exists.
• b) Criterion - the level of assurance that you
  decide must be met before you take action.
  Involves higher mental processes. You set
  criterion based on expectations and
  consequences of inaccuracy.
      Signal-Detection Theory
• For example - at a party, you order a
  need to pay attention so that you will be able to
  detect the appropriate signal (doorbell),
  especially since there is a lot of noise at the
  party. But when you first order the pizza, you
  know it won't be there in 2 minutes, so you don't
  really pay attention for the doorbell. As the time
  for the pizza to arrive approaches, however,
  your criterion become more
  focused on the doorbell and less on extraneous
Signal-Detection Theory
• A) The visual system works on sensing and
  perceiving light waves. Light waves vary in their
  length and amplitude:
• a) Wave length (also referred to as frequency,
  since the longer a wave, the less often/quickly it
  occurs) - affects color perception (ex.,
  red=approx 700, yellow approx 600)
• b) Wave amplitude (this is the size/height of the
  wave) - affects brightness perception.
           Structure of the Eye
• 1) Cornea - the round, transparent area that allows light
  to pass into the eye.
• 2) Lens - the transparent structure that focuses light onto
  the retina.
• 3) Retina - inner membrane of the eye that receives
  information about light using rods and cones. The
  functioning of the retina is similar to the spinal cord -
  both act as a highway for information to travel on.
• 4) Pupil - opening at the center of the iris which controls
  the amount of light entering the eye. Dilates and
• 5) Rods & Cones - many more rods (approximately 120
  million) than cones (approx 6.4 million).
Structure of the Eye
            Rods and Cones
• a) Cones - visual receptor cells that are
  important in daylight vision and color vision.
• The cones work well in daylight, but not in dim
  lighting. This is why it is more difficult to see
  colors in low light.
• most are located in the center of the
  retina...called the FOVEA, which is a tiny spot in
  the center of the retina that contains ONLY
  cones...visual acuity is best here.
• SO...when you need to focus on something you
  attempt to bring the image into the fovea.
            Rods and Cones
• b) Rods - visual receptor cells that are important
  for night vision and peripheral vision.
• The rods are better for night vision because they
  are much more sensitive than cones.
• In addition, the rods are better for peripheral
  vision because there are many more on the
  periphery of the retina. The cones are mostly in
  and around the fovea but decrease as you go
• To see best at night, look just above or below
  the object...this keeps the image on the rods.
Rods and Cones
           Color and Vision
• C) Seeing In Color - we can see many
  colors, but only have 3 types of cones that
  receive information about color. We have
  cones that pick up light waves for red,
  green, and blue.
Color and Vision
        Color Vision Theories
• 1) Trichromatic Theory - this theory
  indicates that we can receive 3 types of
  colors (red, green, and blue) and that the
  cones vary the ratio of neural activity (Like
  a projection T.V.). The ratio of each color
  to the other then determines the exact
  color that we see.
Color Vision Theories
       Color Vision Theories
• 2) Opponent-Process Theory - color
  perception depends on the reception of
  pairs of antagonist colors. Each receptor
  can only work with one color at a time so
  the opponent color in the pair is blocked
  out. Pairs = red-green, blue-yellow, black-
  white (light-dark).
Color Vision Theories
• Much of our understanding of how and why we
  perceive things comes from Gestalt Psychology
• For example - one of the most well known
  Gestalt principles is the Phi Phenomenon, which
  is the illusion of movement from presenting
  stimuli in rapid succession. When you see a
  cartoon or running Christmas lights, you see
  movement (although none actually exists)
  because of this principle.
• A) Gestalt Principles of Perceptual Organization
• 1) figure-ground - this is the fundamental way
  we organize visual perceptions. When we look at
  an object, we see that object (figure) and the
  background (ground) on which it sits. For
  example, when I see a picture of a friend, I see
  my friends face (figure) and the beautiful Sears
  brand backdrop behind my friend (ground).
Figure Ground
• simplicity/pragnanz (good form) - we group
  elements that make a good form.
  However, the idea of "good form" is a little
  vague and subjective. Most psychologists
  think good form is what ever is easiest or
  most simple.
• 3) Proximity - nearness=belongingness.
  Objects that are close to each other in
  physical space are often perceived as
  belonging together.
• 4) Similarity—As you probably guessed,
  this one states that objects that are similar
  are perceived as going together. For
  example, if I ask you to group the following
  objects: (* * # * # # #) into groups, you
  would probably place the asterisks and the
  pound signs into distinct groups.
• Continuity - we follow whatever direction
  we are led. Dots in a smooth curve appear
  to go together more than jagged angles.
  This principle really gets at just how lazy
  humans are when it comes to perception.
• Closure - we tend to complete a form
  when it has gaps.
            Common Fate
• Common fate - elements that move
  together tend to be grouped together. For
  example, when you see geese flying south
  for the winter, they often appear to be in a
  "V" shape.
Common Fate
• Reversible Figures - ambiguous sensory
  information that creates more than 1 good
  form. For example, the picture of two faces
  looking toward each other that is also a
• Impossible Figures - objects that can be represented in
  2-dimensional pictures but can not exist in 3-dimensional
  space despite our perceptions. You know the artist,
  Escher who draws the pictures like...the hands drawing
  each other, the waterfall that goes down and stays level
  at the same time, etc...
• Pain is an unpleasant yet important function for
  survival: warning system (but not all pain is
  needed for survival).
• There are two different pathways to the brain on
  which pain can travel - information brought from
  free nerve endings in the skin to the brain via
  two different systems:
• 1) Fast pathways - registers localized pain
  (usually sharp pain) and sends the information
  to the cortex in a fraction of a second. EX. - cut
  your finger with a knife.
• Slow pathways - sends information
  through the limbic system which takes
  about 1-2 seconds longer than directly to
  the cortex (longer lasting, aching/burning).
Slow Pathways
    Factors in Pain Perception
• 1) Expectations - research shown that our
  expectations about how much something will
  hurt can effect our perception.
• Melzack - indicated that believing that something
  will be very painful helps us prepare for it.
• For example - child birth: Lamaze method falsely
  leads us to believe it won't be painful. Maybe if
  we know it will be bad we can adequately
  prepare to handle it.
Factors in Pain Perception
    Factors in Pain Perception
• Personality - people with negative types of
  personalities often have more pain. E
• For example - a very uptight person may
  experience muscle pains, back pains, etc.
Factors in Pain Perception
     Uptight Person
    Factors in Pain Perception
• Mood - bad moods, angry, unhappy, etc, can
  lead to the experience of increased pain.
• For example - study manipulated moods of
  subjects then asked them to complete
  questionnaires of pain perception. Those in
  negative mood group reported significantly more
  pain than other subjects.
• So, it seems that our brains can regulate,
  control, determine, and even produce pain.
Factors in Pain Perception
   Moods Affect Pain
• Gate Control Theory (Melzack & Walls, 1965) -
  incoming pain must pass through a "gate"
  located in the spinal cord which determines what
  information about pain will be sent to the brain.
  So, it can be opened to allow pain through or
  closed to prevent pain from being perceived.
• The Gate - actually a neural network controlled
  by the brain. Located in an area of the spinal
  cord called the Substansia Gelatinosa. There
  are two types of nerve fibers in this area:
• A) Large - sends fast signals and can prevent
  pain by closing the gate.
• b) Small - sends slower signals which open the
  gate. So - when pain occurs it is because the
  large fibers are off and the small are on, opening
  the gate.
• Since the gate is controlled by the brain, he
  factors discussed earlier (expectations, mood,
  personality) influence the functioning of the gate.
Gate Control Theory
• Contradiction to Gate Control Theory:
• 1) Endorphins - the body's own pain killers
  (morphine-like). May explain acupuncture,
  acupressure, and pain tolerance during
  last two weeks of pregnancy, etc.
            THEORIES OF PAIN
• ability to feel pain, pressure, temperature, and many
  other types of sensations including pain in a limb that
  does not exist (either amputated or born without).
• the feelings and the pain are sometimes so life-like that
  person attempts to pick things up with phantom hand,
  step with phantom foot or leg, etc. Often person feels
  phantom moving in perfect coordination with the rest of
  the body - some report a missing arm extending outward
  at a 90 degree angle so they turn sideways when going
  through a doorway.
• may occur right after amputation or not until years later.
PHANTOM LIMBS Explanations
• 1) The neuroma explanation - remaining nerves in the
  stump grow into nodules (neuromas) at the end of the
  stump continue to fire signals. Signals follow the same
  pathways the brain as when the appendage existed.
• 2) The spinal cord explanation - neurons in the spinal
  cord that are no longer receiving information from the
  lost appendage continue to send information to the brain.
• Problem - studies have shown that when areas in the
  spinal cord are severed often feelings still being
  perceived from areas that meet the spinal cord in lower
  areas (below separation in spinal cord).
PHANTOM LIMBS Explanations
• The brain explanation - signals in the somatosensory
  circuits of the brain change when the limb is lost which
  produce the phantom...the brain compensates for the
  loss or altered signals. This has been expanded - brain
  contains a network of fibers that not only respond to
  stimulation but continually generates a pattern of
  impulses that indicate that the body is intact and
  functioning. Thus, the brain creates the impression that
  the limb exists and is al right. This system may be
• 4) The hardwired explanation - we may have a biological
  makeup to be born with all of our appendages. So, when
  we are born w/o one or lose one, the nerves are still
  there and are still going to send the information.
Sensations and Perceptions

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