Download - Exam in 12 days
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Exam in 12 days
• in class
• assortment of question types including written answers
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Read this article!
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How does the visual system represent visual information?
• Brainstorm this: what are the different ways the visual system might encode a feature?
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How does the visual system represent visual information?
• Brainstorm this: what are the different ways the visual system might encode a feature?
– “labeled lines” • many different subnetworks of neurons - activity in a network
indicates presence/nature of a feature
– spike timing• absolute rate or # of spikes per second might indicate
presence/nature of a feature• “multiplexed”
– Hybrid of these two
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Visual Pathways
• Themes to notice:
– Contralateral nature of visual system
– Information is organized:• According to spatial location• According to features and kinds of information
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Visual Pathways
• Image is focused on the retina
• Fovea is the centre of visual field– highest acuity
• Peripheral retina receives periphery of visual field– lower acuity– sensitive under low light
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Visual Pathways
• Retina has distinct layers
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Visual Pathways
• Retina has distinct layers
• Photoreceptors– Rods and cones respond to
different wavelengths
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Visual Pathways
• Retina has distinct layers
• Amacrine and bipolar cells perform “early” processing
– converging / diverging input from receptors
– lateral inhibition leads to centre/surround receptive fields - first step in shaping “tuning properties” of higher-level neurons
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Visual Pathways
• Retina has distinct layers
– signals converge onto ganglion cells which send action potentials to the Lateral Geniculate Nucleus (LGN)
– two kinds of ganglion cells: Magnocellular and Parvocellular
• visual information is already being shunted through functionally distinct pathways as it is sent by ganglion cells
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Visual Pathways
• visual hemifields project contralaterally– exception: bilateral
representation of fovea!• Optic nerve splits at optic
chiasm
• about 90 % of fibers project to cortex via LGN
• about 10 % project through supperior colliculus and pulvinar– but that’s still a lot of fibers!
Note: this will be important when we talk about visuospatial attention
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Visual Pathways
• Lateral Geniculate Nucleus maintains segregation:
– of M and P cells– of left and right eyes
P cells project to layers 3 - 6
M cells project to layers 1 and 2