Attention: Summary

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Attention Summary

• Attention chooses which incoming info to process
  further.
• Filter Models
• How when does information get filtered?
• Capacity Models
• Why is attention limited?
• What do the limits tell us about the process?
• Attention is limiting and functional.

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Object Recognition
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Object Recognition Outline

• The Phenomenon Problem of Perception
• Approaches to Object Recognition
• Gestalt Principles
• Constructivist Approaches
• Top-down Influences

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The Phenomenon of Perception

• Visual image on retina consists of a
  2-dimensional pattern of light intensity
  differences.
• Yet we perceive a world of whole, stable
  3-dimensional objects.

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The Phenomenon, Contd

• Light reflected from objects in the world

3-D representation of objects in the world
2-D array of light on retina
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The Problem of Perception

• Input underdetermines the true state of the
  world.
• Need to go beyond the information given to
  interpret input.

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Gestalt Psychology

• Founded c. 1911
• Concerned with explaining Perceptual Organization
• The grouping of parts into larger units.
• The whole is different from the sum of its
  parts!
• Proposed rules about how we organize parts into
  wholes.

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Gestalt Laws of Perception

• Pragnanz (Good Figure)
• A stimulus pattern is perceived so that the
  resulting structure is as simple as possible
• Good Continuation
• Lines follow the smoothest path.
• Similarity
• Like things appear to be grouped together

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Figure Ground Segregation
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Figure-Ground Segregation

• Figure is more thinglike and memorable
• Figure is in front
• Ground is uniform
• Ground extends behind figure
• Figure analysis - seeing fine details
• Ground analysis - seeing large areas
• Predictions? Weisstein Wong (1986)
• Line orientations Figure-ground Perception

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Problems with Gestalt Principles

• Principles dont always hold.
• Offers mainly descriptions and after-the-fact
  explanations.

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Constructivist Approaches

• Emphasize how perceptions are build up out of
  primitives.
• Bottom-up
• Perception occurs in Stages
• 1. Primitives are registered
• 2. Primitives are combined into objects
• What are the primitives?

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Treismans Feature Integration Theory

• Primitives curvature, tilt, color, line ends,
  movement, closed areas
• Primitives are independent.
• Object Recognition involves
• Recognition of primitives.
• Integration of primitives into percept.

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F
C
Z
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Recognition by Components Theory

• Geons 3D primitives
• We recognize an object by perceiving its geons.

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Geons
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Top-Down Influences Assumptions

• Perceptual system makes assumptions about the
  world that go beyond the information given in the
  stimulus array.

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Top-Down Influences Context

• Context in which an object occurs influences our
  ability to identify it.
• Word Superiority Effect
• Identifying Object in Scene
• Constancy

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Word Superiority Effect

• Letters are more easily recognized in a word than
  alone or in a random string of letters.

T
COAT
T?
ACOT
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Identifying Objects in Scenes
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Identifying Objects in Scenes
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Size Constancy
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Summary

• Bottom-up processes are important in object
  recognition.
• Data underdetermine the world.
• Top-down assumptions are necessary to complete
  the picture.