Form Perception

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PSY 3520 Sensation and Perception
Form Perception
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Form Perception Lecture Outline

• Perceptual Organization
• A. The Beginnings of Gestalt Psychology
• B. The Law of Pragnanz
• 1. Form Perception
• 2. Laws of Organization
• C. Problems with the Gestalt Approach
• Modern Extensions of Gestalt Psychology
• A. What stimulus properties are responsible for
  grouping?
• B. How does grouping affect our ability to
  extract information from a display?
• C. How are figure and ground analyzed by the
  visual system?
• Perceptual Processing
• Triesman Feature Integration Theory
• A. Preattentive Stage
• B. Focused Attention Stage

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I. Form Perception

• _____ is an inherent property of all objects
• The perception of objects is easy for humans,
  whereas it is very difficult to design computers
  to perceive objects
• Examples of tasks that are easy for humans yet
  difficult for computers
• 1.
• 2.
• 3.

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We see two, 3-dimensional forms
Humans are able to take a 2-dimensional scene
from the retina and translate the image into a
correct perception of the scene. The visual form
is usually considered to be a composite of more
elementary features. The _______ Psychologists
were interested in perceptual organization how
these elementary features were grouped into
larger units.
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The Beginnings of Gestalt Psychology

• Gestalt Psychology was founded in 1912 by Max
  Wertheimer
• 1910 he discovered ___________ (the
  __________________)
• Movement is perceived between 2 stationary
  stimuli
• Concluded __________________________________
• ___________________________________

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The Beginnings of Gestalt Psychology

• The Gestalt Psychologists rejected the idea that
  perceptions are constructed from sensations
• They believed the stimulus must be considered as
  a whole

The contours of the cube are not physically
present they are caused by the rest of the
configuration.
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The Beginnings of Gestalt Psychology

• Wolfgang Köhler and Kurt Koffka were also
  involved in the beginnings of Gestalt Psychology
• The Gestalt Psychologists suggested that there
  were laws of organization
• They wanted to determine the rules that describe
  what your perception will be given certain
  stimulus conditions

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Laws of Organization

• The laws of organization are a series of rules
  that describe what your perception will be given
  certain stimulus conditions
• Law 1 Law of Pragnanz (German means good
  figure)
• The Law of Pragnanz is the central law of Gestalt
  Psychology
• Law of Prgnanz is also called the law of good
  figure and the law of simplicity

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__________________
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_____________________
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______________________
Connected points, either straight or curved are
seen as belonging together Lines are seen in a
way that they follow the smoothest path
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________________________

• Kaswan (1957) memory and continuity

Conclusion Better recall for pairs with good
continuity.
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_______________________
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____________________
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_______________________

• Things that are moving in the same direction
  appear to be grouped together

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______________ ______________________

• Objects form groups if the groups appear familiar
  of meaningful

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Figure-Ground Segregation

• Another issue the Gestalt Psychologists were
  interested in was our perception of figure-ground
  stimuli
• More specifically, they were interested in
  figure-ground segregation - how we perceive
  objects when they form figures against backgrounds

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Figure-Ground Segregation
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Figure-Ground Segregation
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Figure-Ground Segregation
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Properties of Figure-Ground Segregation

• 1.
• 2.
• 3.
• 4.

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Properties of the Stimuli seen as the Figure

• Symmetry
• Convexity
• Convexity usually overpowers symmetry
• Orientation
• Meaning

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What Gestalt Psychology Tells us

• Gestalt Psychology tells us that we have a number
  of laws of organization that help govern the way
  we group parts of a stimulus together and also
  the way we separate figure from ground.

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Problems with the Gestalt Approach

• The application of the law of simplicity how
  can you tell what is the simpler perception?
  There is no way to measure simplicity.
• How applicable are the Gestalt laws to real life?
  What happens when we move from the 2-dimensional
  pictures to the 3-dimensional world?

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Problems with the Gestalt Approach

• What happens when two Gestalt laws conflict with
  one another?

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• We actually do see two asymmetrical patterns, but
  the resulting pattern should be as simple as
  possible.
• What other Gestalt law takes over?

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Problems with the Gestalt Approach

• 1
• 2
• 3
• 4

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II. Modern Extensions of Gestalt Psychology

• Modern researchers have gone beyond the
  descriptive level used by the Gestalt
  psychologists
• Three questions we will try to answer using the
  more quantitative approaches used by modern
  researchers

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• What stimulus properties are responsible for
  grouping?
• Olson Attneave (1970) found orientation to be
  an important property for grouping.
• How does grouping affect our ability to extract
  information from a display?
• Prinzmetal Banks (1976 1977)
• How are figure and ground analyzed by the visual
  system?
• Julesz (1978) and Weisstein Wong (1986)

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III. Perceptual Processing

• The observer carries out mental operations on the
  stimulus to arrive at a perception of the
  stimulus.
• Perception involves an active observer.
• Information processing and perception the whole
  is constructed from information taken from its
  smaller parts.

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_______________________

• The focus now becomes what are the basic units
  of analysis used by the visual system?
• Anne Triesman approached this by proposing that
  perception takes place in two or more stages.

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________________________

• Two stages of processing
• 1.
• 2.

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Preattentive Stage

• Processing is _______________
• No conscious attention is required because
  processing occurs automatically

Triesman suggests that primitives are extracted
at the preattentive stage. Primitive basic
property of a stimulus Triesman suggests that
primitives have pop-out boundaries
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• Triesman investigated primitives using visual
  search tasks
• Visual Search Task identify a target stimulus
  in a field of distractors.

The O pops out because of its curvature
property.
This task takes longer because the target shares
properties with distractors.
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• Triesman identified the following as primitives

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Focused Attention Phase

• The primitives that are extracted in the
  preattentive stage are combined in the focused
  attention stage.
• This stage is NOT automatic conscious attention
  is required.

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Because primitive features are shared, conscious
attention is required.
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