CORTICAL MECHANISMS
OF VISION
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Outline
1. The Parallel, Functionally Segregated
Hierarchical Model of Perception
2. Cortical Mechanisms of Vision
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a. Scotomas and Blindsight
b. Completion
c. Secondary Visual Cortex and Association Cortex
d. Visual Agnosia
The Current Parallel, Functionally Segregated
Hierarchical Model of SensorySystem Organization
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Parallel: sensory systems are organized so that information
flows between different structures simultaneously along multiple
pathways
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Functionally Segregated: There are divisions of labor at the
different hierarchical levels
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Explicit –– a sensory system for consciously seeing things
Implicit –– a sensory system that helps us interact with objects in
space.
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.
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Primary
Secondary
Association
Vertemnus (1591) by
Guiseppe Arcimboldo
The Vegetable Gardener
(1590)
Neural Correlates?
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There is evidence that selective attention occurs by strengthening the
neural responses to attended-to aspects and by weakening the
response to others.
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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
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Does this face belong to the same person?
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face recognition activates the ventral visual pathway – is this face the same
person you saw before?
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fMRI
When attending to location - dorsal stream is activated.
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Is this face in the same position as the last face you saw?
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face position activates the dorsal visual pathway – is this face in the same
location as the face you saw before?
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fMRI
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Primates
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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
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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