Ethical Issues in Psychological Research

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					Perception
z We have previously examined the sensory processes
  by which stimuli are encoded.
z Now we will examine the ultimate purpose of sensory
  information
z PERCEPTION - the conscious representation of the
  external environment.
z Perception involves the selection, organization, and
  interpretation of sensory information.
z Perception quickly became one of psychology’s
  primary concerns as early researchers attempted to
  explain illusions.
Fact or Falsehood

z Understanding illusions provides important
  clues to the ordinary mechanisms of
  perception.
z Infants just learning to crawl do not perceive
  depth.
z Persons who have sight in only one eye are
  totally unable to gauge distances.
z The moon appears larger at the horizon than
  in the sky because distance cues make it
  appear closer.
Fact or Falsehood

z A person who is born blind but gains sight as
  an adult cannot recognize common shapes
  and forms.
z If required to look through a pair of glasses
  that turns the world upside down, we soon
  adapt and coordinate our movements without
  difficulty.
z If people are told that an infant is “David,”
  they are likely to see “him” as bigger and
  stronger than if the same infant is called
  “Diana.”
Fact or Falsehood

z Psychics have frequently been successful in
  helping the police solve crimes.
z Laboratory evidence clearly indicates that
  some people do have ESP.
Selective Attention

z Selective attention means that at any
  moment we focus our awareness on only a
  limited aspect of all that we experience.
z Until reading this sentence, you have been
  unaware that your shoes are pressing against
  your feet or that your nose is in your line of
  vision. Now, suddenly, your attentional
  spotlight shifts. Your feet feel encased, your
  nose stubbornly intrudes on the page before
  you.
Selective Attention

z The cocktail party effect is our ability to
  attend selectively to only one voice among
  many.
z Change blindness experiment. Page 233 in
  book
Perceptual Illusions

z Illusions mislead us by playing on the ways
  we typically organize and interpret our
  sensations.
z Understanding illusions provides valuable
  clues to the ordinary mechanisms of
  perception.
Perceptual Illusions

z Is AB or BC   z See pages 234
  longer?         and 235 in your
                  book for several
                  examples of
                  perceptual
                  illusions.
Perceptual Organization
z Some of the best examples that
  perception involves organization of
  sensory input was provided by the
  Gestalt Psychologists.
z Gestalt psychologists hypothesized
  that “the whole is greater than the
  sum of the parts.”
z They were interested in showing the
  global nature of our perceptions
Perceptual Organization

z Our yen for assembling visual features into
  complete forms involves bottom-up
  processing, starting with entry-level sensory
  analysis, as well as top-down processing that
  uses our experiences and expectations to
  interpret those sensations.
z Sensation and perception blend into one
  continuous process, progressing upward from
  specialized detector cells and downward
  from our assumptions.
Figure and Ground
z Gestalt
  Psychologists also
  thought that an
  important part of our
  perception was the
  organization of a
  scene in to its:
z Figure - the object of
  interest
z Ground - the
  background
Figure and Ground
Gestalt Grouping
Principles
z Gestalt theorists argued that our perceptual
  systems automatically organized sensory
  input based on certain rules.
  y Proximity: we group nearby figures together
  y Similarity: we group figures that are similar to each
    other together.
  y Closure: we fill in gaps to create a complete, whole
    object
  y Good Continuation: we organize stimuli into smooth,
    continuous patterns
  y Connectedness: When they are uniform and linked,
    we perceive spots, lines, or areas as a single unit.
Organizing Stimuli
Depth Perception

z One of our more important perceptual
  abilities involves seeing in three-
  dimensions
z Depth perception is difficult because
  we only have access to two-
  dimensional images
z How do we see a 3-D world using only
  the 2-D retinal images?
Depth Perception Cues

z Cue - stimulus characteristics
  that influence our perceptions
z We are able to see in 3-D
  because the visual system can
  utilize depth cues that appear
  in the retinal images.
Types of Depth Cues

z Depth cues are usually divided into
  categories, we will consider two types
  of depth cues:
z Monocular - depth cues that appear in
  the image in either the left or right eye
z Binocular - depth cues that involve
  comparing the left and right eye
  images
Binocular Cues

z Convergence
  y When you look at a distant object, the lines
    of vision from your eyes are parallel.
    However, when you look at something 50
    feet or less in distance, your eyes must
    converge (turn in) to focus the object.
z Retinal Disparity
  y A difference in the images that reach the
    right and left eyes. RD is based on the fact
    that the eyes are about 2.5 inches apart.
    Because of this, each eye receives a
    slightly different view of the world.
Binocular Depth Cues

z Monocular depth cues allow us to see in
  3-D with the view of only one eye, but
  our best depth perception occurs if we
  look through both eyes.
z This is because our right and left eyes
  see a slightly different view of the world.
z This difference between the image in the
  two eyes is know as Retinal Disparity.
Autostereogram

z Another way to create the illusion of
  depth through binocular stereopsis is
  with an Autostereogram.
z An autostereogram is formed by
  superimposing two repeating patterns
z The two patterns are slightly offset,
  and when viewed properly, this offset
  is seen as a binocular disparity.
Autostereogram
Monocular Depth Cues

  z   Relative Size
  z   Interposition
  z   Relative Clarity
  z   Texture gradient
  z   Relative Height
  z   Relative Motion
  z   Linear Perspective
  z   Light and Shadow
  z   Position relative to Horizon
Relative Size
Interposition
Relative Clarity
Texture Gradient
Relative Height
Relative Height
Linear Perspective
Ponzo Illusion
 z Converging lines indicate that top line is
   farther away than bottom line
Light and Shadow
Motion Perception

z Your brain computes motion based partly on
  its assumption that shrinking objects are
  retreating (not getting smaller) and enlarging
  objects are approaching.
z Large objects, such as a train, appear to
  move more slowly than smaller objects, such
  as a car moving at the same speed.
Motion Perception

z Marquees and holiday lights sometimes
  create another illusion of movement using
  the phi phenomenon.
z When two adjacent stationary lights blink on
  and off in quick succession, we perceive a
  single light moving back and forth between
  them.
Ames Room
z The Ames room is designed so that the
  monocular depth cues give the illusion that the
  two people are equally far away
Other Size-Distance
Illusions
z In each of these
  examples, the
  top and bottom
  lines are actually
  the same length.     (a) Müller-Lyer illusion
z In each case the
  top line looks
  longer.
z Why?

                         (b) Ponzo illusion
Muller-Lyer Illusion

z Perceptual psychologists
  have hypothesized that
  the top horizontal line
  looks longer because it
  also looks farther away.
z Specifically, the inward
  pointing arrows signify
  that the horizontal line is
  closest to you, and the
  outward pointing arrows
  signify the opposite case.
Perceptual Constancy

z When viewing conditions change, the retinal
  image changes even if the objects being
  viewed remain constant.
z Example: as a person walks away from you
  their retinal image decreases in size.
z important function of the perceptual system
  is to represent constancy in our environment
  even when the retinal image varies.
Size Constancy

z Cylinders at
  positions A and B
  are the same size
  even though their
  image sizes differ              Point B
z The depth cues such
  as linear
  perspective and
  texture help the
  visual system judge
  the size accurately   Point A
Shape Constancy

z It is hard to tell if the
  figure on the upper
  right is a trapezoid or
  a square slanted
  backward.

z If we add texture, the
  texture gradient helps
  us see that it is
  actually a square.
Lightness Constancy

z We perceive an object as having a constant
  lightness even while its illumination varies.
z Perceived lightness depends on relative
  luminance – the amount of light an object
  reflects relative to its surroundings.
Perceptual Interpretation

z Sensory Deprivation and Restored Vision
   y In both humans and animals, a period of
     sensory restriction does no permanent
     harm if it occurs later in life.

z Perceptual Adaptation
   y Humans adapt to a distorted environment
     rather quickly.
Perceptual Set

z Our experiences, assumptions, and
  expectations may give us a perceptual set, or
  mental predisposition, that greatly influences
  what we perceive.
   y Isn’t it weird when you see your teacher at
     the grocery store?
z Schemas determine our perceptual set.
   y Children’s drawings reflect their schemas
     of reality, as well as their abilities to
     represent what they see.
Claims of ESP
z Telepathy, or mind-to-mind communication—
  one person sending thoughts to another or
  perceiving another’s thoughts.
z Clairvoyance, or perceiving remote events,
  such as sensing that a friend’s house is on
  fire.
z Precognition, or perceiving future events,
  such as a political leader’s death or a
  sporting event’s outcome.
z Psychokinesis, or “mind over matter,” such
  as levitating a table or influencing the roll of
  a die.

				
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