Download Primary Visual Pathway

• Lab write up due this Friday
• Proposal due Monday March 6
Late reports, one mark out of 20 for each
day late.
Ch. 11
• Vision - central processes
• Ultimately visual perception
– Also:
• Adjust size of the pupil
• Direct eyes to the targets of interes
• Regulate homeostatic behaviors to L/D cycle
Primary Visual Pathway
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Primary Visual Cortex
• AKA
– Striate cortex
– Brodmann’s area 17 or VI
Optic Disc
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Blind Spot:
Test your blind spot.
Optic disc is located on the nasal side of the
retina.
With both eyes open, information about the
corresponding region of visual space comes
from the temporal side of the contralateral
retina.
Blind Spot
• With one eye, blind spot is undetected.
• Why?
– Visual cortex receptive fields fill in with
cortical mechanisms that integrate
information from the visual field
(somehow).
Optic Disc
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Optic Chiasm
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•x
Optic Tract
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Decussation
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Ganglion cell axons to lateral geniculate nucleus
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Another target of ganglion cells:
Pretectum co-ordinates pupillary light reflex
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Another target of ganglion cells:
suprachiasmatic nucleus
(Retino-hypothalamic pathway)
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Suprachiasmatic nucleus
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Another target for ganglion cells:
superior colliculus
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Another target for ganglion cells:
superior colliculus
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RETINOTOPIC REPRESENTATION OF
THE VISUAL FIELD
• Each eye sees a part of the visual
space that defines its visual field
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Visual Field
• Receive info from both fields
• Nasal, temporal, superior and inferior
divisions.
• Binocular vision
• Binocular hemifield
VISUAL FIELD
• Temporal visual fields are more
extensive than the nasal visual fields
• Vision in the peripheral field is monoocular
• Most of the rest of the visual field is
seen by both eyes.
• Map is maintained in the LGN
– Maintained by the visual cortex
– Fovea is in the back of the visual cortex
– Peripheral is progressively more anterior
– Sensory surface reflects density of
receptors
Upper visual field
• Calcarine
sulcus
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Hubel and Weisel
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Hubel and Weisel
• Visual cortex responses using microelectrodes
– Respond ot light/dark bars or edges
– Only if in a particular orientation
– Peak frequency depends on angle,
preferred orientation
– All edges representations were equally
represented
– Orientation selective neurons
Visual Cortex
• Simple cells - Spatially distinct on and off
zones
• Complex cells - receptive field has a mixture
of on and off zones
• Length cells - respond to length of a bar that
was moved across a receptive field
• Direction cells - respond to direction of a bar
moving across the receptive field.
• Still do not understand the mechanisms
responsible for generating these
selective responses.
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Complex cell
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Complex
Cell
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Binocular vision
• Individual LGN neurons are mono-ocular
driven.
• How are neurons with different receptive
fields arranged within the striate cortex?
• A column of cells has similar response
properties
• Adjacent columns have similar response
properties.
Visual Cortex
• Composed of repeating units that
contain all the neuronal machinery
necessary to analyze a small region of
visual space for a variety of different
stimulus attributes.