Perception

							           Sensory Adaptation
• Our diminishing sensitivity to an
  unchanged stimulus
• Do you feel your underwear all
  day?
• Do you feel your shoes all day?
                 Perception




   The process of organizing and interpreting
information, enabling us to recognize meaningful
              objects and events.

  We see not how the world is but how it is useful to us
Top-Down Processing
          • We identify something
            b/c our brain tells us what
            the object is (prior
            knowledge)
          • We perceive by filling the
            gaps in what we sense.
          • I _ant ch_co_ate ic_
            cr_am.
          • Based on our experiences
            and schemas.
          • If you see many old men in
            glasses, you are more apt
            to process a picture of an
            old man (even when you
            may be in error).
• Also called feature
  analysis                     Bottom-Up
• We use the features on       Processing
  the object itself to build
  a perception
• No prior knowledge
• Takes longer than top-
  down but is more
  accurate
                                  Click to see an example
                                  of bottom –up
                                  processing.
    Cocktail-party phenomenon
• The cocktail party effect
  describes the ability to
  focus one's listening
  attention on a single talker
  among a mixture of
  conversations and
  background noises, ignoring
  other conversations
• Form of selective attention
              Selective Attention
• The focusing of conscious
  awareness on a particular
  stimuli
• You didn’t notice consciously
  feel your shirt until you read
  this 
• Inattentional Blindness: failing
  to see visible objects when our
  attention is directed elsewhere
• Change Blindness: failing to       Click on the mouse to
  notice changes in the              see an example of
                                     change blindness.
  environment
                  Thresholds
• Absolute Threshold: the minimum amount of
  stimulation needed to detect a light, sound,
  pressure, taste, odor… 50% of the time
  – Psychophysics: the study of relationships between
    physical characteristics of stimuli (like intensity)
    and our psychological experience of them (look
    for absolute thresholds)
  – Ex: mtn on dark night, see light miles away
  – Ex: vision & hearing tests
  – Ex: mosquito ring tones
  – Ex: shopkeeper
          Signal Detection Theory
• Theory that predicts when we detect
  weak signals amid background
  stimulation
   – Says absolute thresholds are not
     really absolute
• So many factors affect what we can
  sense
   – time of day? did you eat
     breakfast? do they exercise? Did
     you get enough sleep? …
• 4 possibilities:
   – Hit-signal present & sensed
   – Miss-signal present but not
     sensed
   – False Alarm-signal not present but
     sensed
   – Correct Rejection-signal absent &
     not sensed
        (Just Noticeable Difference)
           Difference Threshold
•   The smallest amount of change
    needed to detect in a stimulus
    before we detect a change
•   Why would you need this?
      • Ex: hearing your friend’s
         voice over other voices in
         the hallway
      • Ex: My mom’s whistle
      • Ex: Musician detecting
         differences when tuning
         an instrument
                 Weber’s Law
• The greater the magnitude
  of the stimulus, the larger
  the differences must be to
  be noticed
  • Ex: if you are listening to the
    tv at volume 40, the JND
    occurs when you decrease the
    volume by 4
  • If you are listening to tv
    volume at 20, the JND occurs
    when you decrease the
    volume by 2
Perceptual Ideas
Figure Ground Relationship

           • We organize what we
             see into objects (the
             figures) that stand out
             from their
             surroundings (the
             background)
           • We always organize
             stimulus into a figure
             seen against the
             ground
Gestalt Psychology
• Gestalt psychologists focused on how
  we GROUP objects together
• We innately look at things in groups
  or as a WHOLE, not as isolated
  elements (we want to see the forest,
  not the trees)
• Proximity (group objects that are
  close together as being part of same
  group- 3 sets of 2 lines, not 6)
• Similarity (objects similar in
  appearance are perceived as being
  part of same group- vertical columns
  of similar shapes not horizontal of
  different)
• Continuity (objects that form a
  continuous form are perceived as
  same group- 1 wavy, 1 straight line)
• Connectedness (b/c they are uniform
  & linked we think of the 2 dots and
  line as one unit)
• Closure (like top-down processing…we
  fill gaps in if we can recognize it)   CLOSURE
Depth Cues
    • Depth Perception: allows us to
      judge distance
       – Our retinas pick up 2D but we
          see 3D
    • Eleanor Gibson and her Visual
      Cliff Experiment.
    • If you are old enough to crawl,
      you are old enough to see depth
      perception.
    • We see depth by using two cues
      that researchers have put in two
      categories:
       – Monocular Cues
       – Binocular Cues
Binocular Cues
       • We need both of our
         eyes to use these cues.
       • Retinal Disparity: as an
         object comes closer to
         us, the differences in
         images between our
         eyes becomes greater
       • Convergence (as an
         object comes closer our
         eyes have to come
         together to keep
         focused on the object)
    Monocular Cues
• You really only need
  one eye to use these
  (used in art classes to
  show depth).
• Linear Perspective:
  parallel lines appear to
  converge w/ distance
• Interposition: if one
  object partially block
  our view of another we
  think it’s closer
• Relative Height: we perceive
  objects higher in our field of
  vision as farther away
• Relative Size: the smaller
  the object the farther away
  we think it is
• Light and Shadow: given 2
  identical objects the
  dimmer one seems farther
  away
Constancy
     • Objects change in
       our eyes constantly
       as we or they
       move….but we are
       able to maintain
       content perception
     • Shape Constancy
     • Size Constancy
     • Brightness
       Constancy
            Perceived Motion
• Stroboscopic effect
  (flip book effect,
  cartoons)
• Phi phenomenon:
  movement illusion when
  2 or more adjacent
  lights are blink on and
  off in quick succession
• Autokinetic Effect (if
  people stare at a white
  spotlight in a dark
  room, it appears to
  move)
    Perceptual Constancy
•   Size Constancy
•   Lightness Constancy
•   Color Constancy
•   You saw all of these
    in the “Brain
    Games” video
                Perceptual Set
• What do these letters spell? FOLK
• How about these? CROAK
• And these? SOAK
• What do we call the white of an egg?
   – NO!!! IT’S AN EGG WHITE!!!
• Perceptual Set: a mental predisposition to perceive
  one thing and not another