CORTICAL MECHANISMS OF VISION

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CORTICAL MECHANISMS OF VISION

• Outline
• 1. The Parallel, Functionally Segregated
  Hierarchical Model of Perception
• 2. Cortical Mechanisms of Vision
• a. Scotomas and Blindsight
• b. Completion
• c. Secondary Visual Cortex and Association Cortex
• d. Visual Agnosia

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The Current Parallel, Functionally Segregated
Hierarchical Model of Sensory-System Organization

• Parallel sensory systems are organized so that
  information flows between different structures
  simultaneously along multiple pathways
• Explicit a sensory system for consciously
  seeing things
• Implicit a sensory system that helps us
  interact with objects in space.
• Functionally Segregated There are divisions of
  labor at the different hierarchical levels
• Some neurons respond to motion, some to color,
  and so on.
• Hierarchical information flows through brain
  structures in order of their increasing
  neuroanatomical and functional complexity.
• Primary
• Secondary
• Association

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Vertemnus (1591) by Guiseppe Arcimboldo
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The Vegetable Gardener (1590)
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Neural Correlates?

• There is evidence that selective attention
  occurs by strengthening the neural responses to
  attended-to aspects and by weakening the response
  to others.
• Anticipation of a stimulus increases neural
  activity in the same circuits affected by the
  stimulus itself.
• When attempting to recognize faces - ventral
  stream is activated
• Does this face belong to the same person?
• face recognition activates the ventral visual
  pathway is this face the same person you saw
  before?
• fMRI
• When attending to location - dorsal stream is
  activated.
• Is this face in the same position as the last
  face you saw?
• face position activates the dorsal visual pathway
  is this face in the same location as the face
  you saw before?
• fMRI

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• Primates
• Recorded from neurons in the prestriate area that
  is part of the ventral stream that are particular
  responsive to color.
• Some cells responded to red some to green
• Monkeys were taught to perform a task that
  required attention to a red cue.
• The activity of red neurons was increased,
  whereas the activity of green neurons was reduced