Download 02 The Visual System

The Visual System
Psychology 355
Introduction
I.
Neurons in the visual system
A.
Neural processing resulting in perception
II. Parallel pathway serving conscious visual
perception originate in the retina
A.
Progress to lateral geniculate nucleus, primary
visual cortex & higher order visual areas in
temporal and parietal lobes
III. Neuronal receptive fields
A.
Sensitive to different facets of the visual input
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The Retinofugal Projection
The Optic Nerve,
Optic Chiasm,
Optic Tract
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The Retinofugal Projection
The Optic Nerve,
Optic Chiasm,
Optic Tract,
LGN,
Optic Radiations
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The Retinofugal Projection
I.
Right and Left Visual Hemifields
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The Retinofugal Projection
Targets of the Optic Tract
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The Retinofugal Projection
Targets of the Optic Tract
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The Retinofugal Projection
Targets of the Optic Tract
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The Retinofugal Projection
I.
Nonthalamic Targets of the Optic Tract:
A.
Hypothalamus: Biological rhythms,
including sleep and wakefulness
B.
Pretectum: Size of the pupil; certain
types of eye movement
C.
Superior colliculus: Orients the eyes in
response to new stimuli
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The Lateral Geniculate Nucleus (LGN)
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The Lateral Geniculate Nucleus (LGN)
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The Lateral Geniculate Nucleus (LGN)
I.
The Segregation of Input by Eye
and by Ganglion Cell Type
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The Lateral Geniculate Nucleus (LGN)
I.
Receptive Fields
A.
Receptive fields of LGN neurons: Identical
to the ganglion cells that feed them
A.
Magnocellular LGN neurons: Large,
monocular receptive fields with transient
response
A.
Parvocellular LGN cells: Small,monocular
receptive fields with sustained response
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The Lateral Geniculate Nucleus (LGN)
I.
Nonretinal Inputs to the LGN
A.
Retinal ganglion cells axons: Not the main
source of synaptic input to the LGN
B.
Primary visual cortex: 80% of the synaptic
inputs
C.
Neurons in the brain stem: Modulatory
influence on neuronal activity
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Anatomy of the Striate Cortex
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Anatomy of the Striate Cortex
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Anatomy of the Striate Cortex
I.
Retinotopy
A.
Map of the visual field onto a target structure (retina,
LGN, superior colliculus, striate cortex) overrepresentation of central visual field
B.
Discrete point of light: Activates many cells in the target
structure
C.
Perception: Based on the brain’s interpretation of
distributed patterns of activity
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Anatomy of the Striate Cortex
I.
Retinotopy
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Anatomy of the Striate Cortex
I.
Lamination of the Striate
Cortex
A.
Layers I - VI
B.
Spiny stellate cells:
Spine-covered dendrites;
layer IVC
C.
Pyramidal cells: Spines;
thick apical dendrite;
layers III, IV, V, VI
A.
Inhibitory neurons: Lack
spines; All cortical layers;
Forms local connections
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Anatomy of the Striate Cortex
Inputs to the Striate Cortex
A.
Magnocellular LGN neurons: Project to layer
IVC
B.
Parvocellular LGN neurons: Project to layer
IVC
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Anatomy of the Striate Cortex
I.
Ocular Dominance Columns
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Anatomy of the Striate Cortex
I.
Inputs to the Striate Cortex
A.
Layer IVC innervates superficial layers
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Anatomy of the Striate Cortex
I.
Outputs of the Striate
Cortex:
A.
Layers II, III, and IVB:
Projects to other cortical
areas
B.
Layer V: Projects to the
superior colliculus and
pons
C.
Layer VI: Projects back to
the LGN
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Anatomy of the Striate Cortex
I.
Cytochrome Oxidase Blobs
A.
Cytochrome oxidase is a
mitochondrial enzyme used
for cell metabolism
B.
Blobs: Cytochrome oxidase
staining in cross sections of
the striate cortex
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Physiology of the Striate Cortex
I.
Receptive Fields
A.
Layer IVC: Monocular; center-surround
B.
Layer IVC: Insensitive to the wavelength
C.
Layer IVC: Center-surround color opponency
II. Binocularity
A.
All layers superficial to IVC: First binocular
receptive fields in the visual pathway
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Physiology of the Striate Cortex
Receptive Field
Simple Cells
Orientation
Selectivity
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Physiology of the Striate Cortex
Receptive Field
Simple Cells
Orientation Selectivity
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Physiology of the Striate Cortex
Receptive Field
Simple Cells
Orientation Selectivity
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Physiology of the Striate Cortex
I.
Receptive Fields
A.
Simple cells: Binocular; Orientationselective; Elongated on-off region with
antagonistic flanks responds to optimally
oriented bar of light
B.
Possibly composed of three LGN cell
axons with center-surround receptive
fields
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Physiology of the Striate Cortex
Receptive Fields
Complex Cells
Direction Selectivity
Neuron fires action potentials in
response to moving bar of
light
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Physiology of the Striate Cortex
Receptive Fields
Complex Cells
Direction
Selectivity
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Physiology of the Striate Cortex
I.
Receptive Fields
A.
Complex cells: Binocular; Orientationselective; ON and OFF responses to the
bar of light but unlike simple cells, no
distinct on-off regions
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Physiology of the Striate Cortex
I.
Receptive Fields
A. Blob Receptive Fields
1. Blob cells: Wavelengthsensitive; Monocular; No
orientation; direction
selectivity
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Physiology of the Striate Cortex
Parallel Pathways:
Magnocellular
Parvocellular
Koniocellular
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Physiology of the Striate Cortex
Cortical Module
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Striate Cortex: Summary
Type
Pyramidal
Pyramidal
Spiney
Spiney
Pyramidal
Pyramidal
Layer
I
II
III
}
IVA
IVB
IVCα
IVCβ
V
VI
Input
Koniocellular,
IVCα, IVCβ
Orientation (simple) V2, V3, V4,
Color (blobs)
Binocular (III)
IVCα
Magnocellular
Parvocellular
Motion (complex)
V2, V5(MT)
IVB, II, III
II, III
Colliculus
LGN
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Beyond Striate Cortex
I.
Dorsal stream
A.
Analysis of
visual motion
and the visual
control of
action
II. Ventral stream
A.
Perception of
the visual
world and the
recognition of
objects
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Beyond Striate Cortex
I.
The Dorsal Stream (V1, V2, V3, MT, MST, Other
dorsal areas)
A.
Area MT (temporal lobe)
1.
Most cells: Direction-selective; Respond
more to the motion of objects than their
shape
B.
Beyond area MT - Three roles of cells in area
MST (parietal lobe)
i.
Navigation
ii.
Directing eye movements
iii. Motion perception
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Beyond Striate Cortex
I.
The Ventral Stream (V1, V2, V3, V4, IT, Other
ventral areas)
A.
Area V4
1.
Achromatopsia: Clinical syndrome in
humans-caused by damage to area V4;
Partial or complete loss of color vision
B.
Area IT
1.
Major output of V4
2.
Receptive fields respond to a wide variety of
colors and abstract shapes
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From Single Neurons to Perception
I.
Visual perception
A.
Identifying & assigning meaning to
objects
II. Hierarchy of complex receptive fields
A.
Retinal ganglion cells: Center-surround
structure, Sensitive to contrast, and
wavelength of light
B.
Striate cortex: Orientation selectivity,
direction selectivity, and binocularity
C.
Extrastriate cortical areas: Selective
responsive to complex shapes; e.g.,
Faces
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From Single Neurons to Perception
I.
From Photoreceptors to Grandmother Cells
A.
Grandmother cells: Face-selective neurons in
area IT?
B.
Probably not: Perception is not based on the
activity of individual, higher order cells
II. Parallel Processing and Perception
A.
Groups of cortical areas contribute to the
perception of color,motion, and identifying
object meaning
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Concluding Remarks
I.
Vision
A.
Perception combines individually identified
properties of visual objects
B.
Achieved by simultaneous, parallel processing
of several visual pathways
II. Parallel processing
A.
Like the sound produced by an orchestra of
visual areas rather than the end product of an
assembly line
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End of Presentation
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