INTRODUCTION TO PSYCHOLOGY

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INTRODUCTION TO PSYCHOLOGY

• Chapter 5
• Perception

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At the end of this Chapter you should be able to

• Understand what Distance Perception is
• Understand what Motion Perception is
• Understand what Form Perception is
• Learn about Attention
• Learn about Visual Illusions

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Visual Perception

• The retinal image is only two-dimensional height
  and width...
• From the two-dimensional images that fall on our
  retinas we somehow are able to see
  three-dimensional objects.
• Seeing objects in three dimensions, or depth
  perception, allows us to estimate distances
  between those objects and us.

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Visual Perception

• Psychologists are particularly interested in the
  cues which enable people to perceive depth and
  distance. These cues may be monocular, effective
  when using one eye as well as two, or binocular,
  requiring the usage of both eyes.

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Depth Distance Perception

• Depth Perception Ability to see
  three-dimensional space and to accurately judge
  distances
• Depth Cues Features that supply information
  about distance and space.

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Depth Distance Cues

• Binocular cues
• We compare the retinal image in one eye to the
  retinal image in the other they differ each
  eye is a slightly different distance from an
  object in the world
• Monocular cues
• Interposition
• Linear perspective
• Texture Gradients

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Binocular disparity
The disparity between the views serves as a
powerful cue for depth
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Monocular Cues Interposition
Interposition When one object partly blocks your
view of another, you perceive the partially
blocked object as farther away
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Monocular Cues Interposition
Interposition The fact that mailbox blocks the
view is a powerful cue that the mailbox must be
closer to the observer than the sport car is
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Monocular Cues Interposition
Madonna of the Magnificat by Sandro Botticelli.
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Monocular Cues Linear Perspective
Linear Perspective Parallel lines that are known
to be the same distance apart appear to grow
closer together, or converge, as they recede into
the distance
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Monocular Cues Linear Perspective
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Monocular Cues Texture Gradient
Texture Gradients The texture of objects tend to
become smoother as the object gets farther away,
suggesting that more detailed textured objects
are closer. 
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Monocular Cues Relative Size
Relative size Larger objects are perceived as
being closer to the viewer, and smaller objects
as being farther away
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Monocular Cues Relative Size
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Monocular Cues Light and Shadow
Monocular cues to Depth light and shadow (A)
Eight circular objects. To most viewers, the one
in the middle looks concave, indented, whereas
other seven look as if they are bulging out. (B)
The same figure rotated 180 degrees. Now, the
middle object looks convex, while others seem
concave. The reason is the location of the
shadow. If the shadow is at the bottom, the
object looks convex, if the shadow is at the top,
the the object looks concave.
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Monocular Cues Light and Shadow
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Monocular Cues Motion Parallax

• When you ride in a moving vehicle and look at the
  side window, the objects you see appear outside
  move in opposite direction
• Objects seem to be moving in different speeds-the
  ones that are closer to you seem to move faster,
  whereas objects far behind seem to move slower

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Monocular Cues Motion Parallax
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Perceptual Constancy

• The tendency to perceive objects as maintaining
  stable properties (e.g., size, shape, brightness,
  and color) despite differences in distance,
  viewing angle, and lighting

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Size Constancy
Size constancy refers to our ability to see
objects as maintaining the same size even when
our distance from them makes things appear larger
or smaller. 
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Shape constancy   
Shape Constancy Perceiving objects as having a
stable or unchanging shape regardless of changes
in the retinal image resulting from differences
in viewing angle
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VIDEO of Julian Beever, an English artist, who
paints sidewalks in an amazing 3-D way....
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Motion Perception

• Perception of an event -motion- rather than an
  object
• Motion tells us what the object is doing.
• Apparent movement
• Eye movement

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Apparent motion

• When intervals between images occur at correct
  timing (not too far apart in time) we perceive
  motion
• This principle used to create motion from stills

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Apparent motion

• In movies, when still pictures are put together,
  it produces the sensation of movement for the
  viewer (audience). Even though there is no ACTUAL
  movement.
• We do not only detect motion but we also
  interpret it.

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Apparent Movement
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Apparent motion

• Motion

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Form Perception

• We can find differences among features
  effortlessly
• Finding a circle in a field of squares is easy
  regardless of how many squares there are
• We need more than features or a simple checklist
  to be able to recognize objects

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What about the variability in objects that we see?

• The same animal but the features look different.
  So how can we classify all of them as a giraffe?

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What about the variability in objects that we see?

• We recognize giraffes as being giraffes whether
  we see them from the side, or the front, or close
  up, or from far away.
• Do we actually pay attention to every detail
  (feature)?
• We only interpret crucial information. We dont
  have time in the real-world to pay attention to
  every little detail. Otherwise we cannot survive!

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Form Perception

• Detecting object features (parts)
• The importance of organization
• Perceptual parsing
• Separating the figure from the ground

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Organizations role in perception

• Features some we ignore, some we attend to
• How do we decide whether to ignore or attend?
• We interpret some features as being part of the
  object, other features as irrelevant
• How do we group together features that belong
  with each other?

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A hidden figure
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Missing features
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Gestalt Psychology

• The German word "Gestalt" roughly means to
  "whole" or "form"
• The whole is greater than the sum of its
  parts. 
• In order to interpret what we receive through our
  senses, we attempt to organize this information
  into certain groups. 
• Sense of shape derived from the whole, not the
  sum of its parts

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Gestalt principles organization

• Perceptual parsing
• Segregating the scene into its constituent
  objects
• The first step to organizing
• Gestalt principles of organization
• Issues of figure/ground
• Similarity
• Proximity
• Good continuation
• subjective contours

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Perseptual Parsing
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Grouping by similarity
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Grouping by proximity
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Good Continuation
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Subjective contours
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Gestalt psychology

• Important Is the object figure or ground?
• Our interpretation of figure / ground will
  influence how we perceive an object

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Reversible figure-ground pattern
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The classical approach to perception

• Emphasis on the active, constructive role of the
  perceiver, who routinely
• Resolves ambiguous figures
• Determines identity of objects based on
  contextual clues and previous knowledge
• Determines identity of objects based on
  contextual clues

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Ambiguous Necker Cube
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Contextual clues (and previous knowledge)
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Illusions How could we make such mistakes?

• Cues sometimes cause an over-estimate or
  under-estimate
• Slight over/under interpretations can cause us to
  misinterpret the information we receive
• Usually
• perceptions are accurate
• are based on relevant experience
• reflect the world we live in

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The Ponzo Illusion
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Brightness Illusion
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Perceptual selection Attention

• What starts the synchrony? One possible
  mechanisms ATTENTION
• Selective control of orientation
• Selective looking
• Difficult when target represents multiple, rather
  than a single, feature

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VIDEO on Attention 1(when you do not expect to
see any changes)VIDEO on Attention 2 (when you
expect to see changes)
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Other modalities

• Hearing much in common with vision
• Sounds must be parsed what goes with what?
• Contexts must be noted Kiss this guy versus
  Kiss the sky have identical sounds involved,
  but different contexts
• Attention crucial determinant of what is heard
• Other modalities less rich for human beings than
  are vision and hearing

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Some final thoughts Seeing, knowing, and the
perceivers active role

• Perception is not knowledge
• Knowledge and perception are mutually influenced,
  but are not the same thing the perceiver and
  the knower are distinct in many instances

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In this experiment, subjects were asked to keep
the track of the ball players in white shirts.
Intent on their task, the subjects were not
paying any attention to the black shirted
players, even though they are looking directly at
them. AND THEY ALSO FAILED TO SEE .....
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VIDEO about the blind Turkish artist Esref Armagan
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Web Links for Optical Illusions

• Mueller-Lyer Illusion
• Brightness Illusion
• Checker-Shadow Illusion

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Attention Demos

• The Stroop Effect

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As fast as you can, read the names of the colors
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As fast as you can, (dont read the word) but
read the name of the color of the word.
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As fast as you can, (dont read the word) but
read the name of the color of the word.
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As fast as you can, (dont read the word) but
read the name of the color of the word.