Chapter 7 - Visual Attention

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Chapter 7 - Visual Attention

• Cognitive overview of the problem of attention

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What is Attention?

• Everybody knows what attention is. It is
  taking possession by the mind, in clear and vivid
  form, of one out of what seem several
  simultaneously possible objects or trains of
  thought. Focalization, concentration of
  consciousness are of its essence. It implies
  withdrawal from some things in order to deal
  effectively with others , and is a condition
  which has a real opposite in the confused, dazed
  scatterbrain state
• William James (1890)

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What is Attention?

• Taking possession of the mind
• Controlling the focus of attention
  intentionality Please pay attention
• one out of what seem several simultaneously
  possible objects
• Our apparent inability to attend to multiple
  things at once
• It implies withdrawal from some things in order
  to deal effectively with others
• Attending has a cost
• Attending is a limited capacity process
• has a real opposite in the confused, dazed
  scatterbrain state
• Attending is the glue that keeps perception
  together

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Attention Selecting some stimuli over others for
further processing

• Why select? Why not process all visual input?
• Limited processing capacity
• Limited processing capacity of what?
• Response systems Two hands, one mouth, etc.
• Input One pair of foveas
• Use of distributed representations When more
  than one pattern is activated simultaneously,
  interference or cross-talk may occur.

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Coping with the problem of interference and cross
talk

• Reducing the degree of distributedness at higher
  levels of visual representation
• Evidence of sparse population codes (e.g., IT
  face representations)
• Binding attributes via synchronized oscillations
• Selective Attention Focusing processing on a
  selected portion of the scene
• Reduces information overload

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Selective Attention

• Selective attention Limits the processing to
  one portion of the scene at a time.
• Stimulus selection could be based on
• location in a (retinotopic map)
• object representation

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Spatial-based Selection

• Posners Spatial Cuing Procedure.
• - See fixation cross
• - Brightness change
• - Respond to target onset
• Fastest response to a target that occurs on the
  cued side (valid) and slowest when target occurs
  on the non-cued side (invalid).

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Object-based Selection

• Task
• Told what dimension(s) to report
• Fixation point
• See target (79 ms)
• Pattern mask
• Report
• Target Two overlapping objects, each with 2
  dimensions
• Box Height Gap
• Line Texture Orientation
• Equally accurate reporting one or two dimensions
  from the same object
• More accurate reporting two dimensions from the
  same object than one dimension from each of two
  objects. (Vecera Farah, 1994, E1 86 gt 80)

After Duncan (1980)
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Visual Attention The Glue that Binds

• We normally experience our complex environments
  as a coherent world of integrated objects.
• Remember Sensory information (i.e., shape,
  color, motion) arrives in parallel and is
  processed by different pathways in brain.
• To create useful mental representations of
  objects, we collect their features, bind them
  into the correct temporal and spatial bundles,
  and interpret these bundles to specify their real
  world origins.
• This process depends upon focused attention.
• If focused attention fails, binding may fail and
  we perceive illusory conjunctions (i.e., upon
  seeing two cars (red Focus and black Echo, may
  falsely report a red Echo).

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Feature Integration Theory Treisman (1998)
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Limited Visual Input

• Although we seem to have a detailed, highly
  veridical and continuous mental representation of
  visual world about us, visual input is limited.
• Visual acuity is good only for foveal focus.
• Eyes movement from one fixation point to another
  while viewing a scene.
• Saccades 3-5 saccades/sec, 40 50 msec each.
• Fixations 300 msec, during which we pick up
  visual information.

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Eye Movements Saccades and Fixations
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Change Blindness

• Failure to detect supraliminal changes in a
  visual scene. (i.e., editing discontinuities in
  movies).
• Flicker technique In your demonstration,
  changes involved color, size, location,
  presence/absence of objects in scene.
• Winter 2006 data (Psych 3450)
• Accuracy Latency
• Central Interest 96 5.5 sec
• Marginal Interest 84 13.5 sec

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Two Empirical Issues to be Addressed from the
Neuroscience Perspective

• How does attention affect visual information
  processing at different stages?
• What neural systems control the allocation of
  attention?