Lect2 Vision 1

8/12/2019 Lect2 Vision 1

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The Visual Pathway


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2

Pathway extends from the

front to the back of thebrain.

Precise retinotopic

organization

Deficits due to lesions of

the pathway give valuable

localizing information.

The Visual PathwayPg. 2

OT

ONOC

VISUALCORTEX

RETINA

VISUAL

FIELD

LGN

OPTIC

RADIATIONS

ON = Optic Nerve

OC = Optic Chiasm

OT = Optic Tract

LGN = Lateral Geniculate Nucleus of Thalamus


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3

Beginning of the PathwayPg. 2


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4

Cells

of theRetina

Pg. 2

Rods and Cones(Receptors)

Ganglion cells axons form the optic nerve

Bipolar cells


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Retinal Quadrants

nose

UTQ UTQ

LTQ LTQLNQLNQ

UNQ UNQ

Right retina Left retina

Papilla (optic

nerve head)

Macula with

fovea centralis

Retina as you would see it through the

ophthalmoscope & the patients pupil

Temporal Hemiretina

UTQ = upper temporal quadrant

LTQ = lower temporal quadrant

Nasal Hemiretina

UNQ = upper nasal quadrant

LNQ = lower nasal quadrant

Horizontal Meridian

Vertical Meridian

Pg. 2

The blind spotin the Visual Field corresponds to the location ofthe optic nerve head on the NASAL side of the retina.


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Visual Fields & the Visual PathwayPg. 2

OT

ONOC

VISUALCORTEX

RETINA

VISUAL

FIELD

LGN

OPTIC

RADIATIONS

ON = Optic Nerve

OC = Optic Chiasm

OT = Optic Tract

LGN = Lateral Geniculate Nucleus of Thalamus

The following slidesbegin with the

visual fields and

then follow the

pathway from theretina to the visual

cortex.


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Blind Spot

15to the temporal side

of the visual field of eacheye

On the horizontalmeridian

Corresponds to the

location of the opticnerve head 15to thenasal side of the retina ofeach eye.

Visual Fields

Demonstration of the Blind Spot:

Draw the star and box on a piece of paper. Close your left eye; Look at the starwith your right eye; Move paper back and forth

until thegreen boxdisappears.

Open your left eye and the box can be seen because even though it was falling on the

blind spot of the right eye, it is not falling on the blind spot of your left eye.

With both eyes open & binocular vision intact, you dont realize that there is a blind

spot since the corresponding spot on the contralateral retina will see the object.

Pg. 3

Temporal Field of

Left EyeNasal Field of

Left Eye

Normal MonocularVisual

Field of Left Eye

F F


Field of Right Eye

UpperFieldof

LeftEye

Lower

Fieldof

LeftEye


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10

Visual Fields:

Binocular

Pg. 3

Normal BinocularVisual Field

F

Right Visual FieldLeft Visual Field

Upper Fields

Lower Fields

Temporal Field of


Left Eye


Field of Left Eye

F F


Field of Right Eye

Understand the difference between the monocular visual field of the left eye vs.the binocular left visual field and vice versa for the right counterparts.

Binocular fieldcombines the two monocular

visual fields with the foveas (F) aligned with

one another. (i.e. the pink area in the imageto the right)

Left Visual Field seen by both the left & right

eyes.

Right Visual Field seen by both the left &

right eyes.

Monocular crescentfor each eye (blue for

left eye & green for right eye) is only seen by

the nasal retina of the same eye.

MonocularCrescent ofRight Eye

MonocularCrescent ofLeft Eye


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Visual Fields:

Binocular

Binocular vision is dependent upon the

extraocular muscles aligning the eyes so

that an image falls on correspondingpoints on the retina of each eye. This is

essential for the brain to perceive a single

image. Diplopia occurs when the images

are not aligned to fall on corresponding

points of each retina.

Pg. 3

Normal BinocularVisual Field

F

Right Visual FieldLeft Visual Field

Upper Fields

Lower Fields

Temporal Field of


Left Eye


Field of Left Eye

F F


Field of Right Eye

Demonstration of the Binocular

Visual Field & Monocular Crescent:

Look straight ahead

Close your right eye

Move your finger to the right

until it disappears

Open right eye to see the pencil-- in the right temporal

monocular crescent of your

visual field.


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Visual Fields Pg. 4

The image of an object in the visual fieldis invertedand reversed right to lefton the retina.

Temporal field of left eye (red & purple) is seen by the nasal retina of the left eye

Nasal field of the left eye (green & yellow) is seen by the temporal retina of the left eye.

Superior field of the left eye (red & green) is seen by the inferior retina of the left eye.

Inferior field of the left eye (purple & yellow) is seen by the superior retina of the left eye.

Similarly, the image is inverted & reversed for the right eye.

Retina ofLeft Eye

Retina ofRight Eye

NOTE:

DOTTED OUTLINE = MONOCULAR

FIELD OF LEFT EYE

SOLID OUTLINE = MONOCULAR FIELD

OF RIGHT EYE

Binocular

Visual Field

MonocularCrescent ofRight Eye

MonocularCrescent ofLeft Eye

Note: To avoid confusion and abide by convention, central representation, visual

deficits, etc. will be described in terms of visual fields and not retinal quadrants.


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VisualPathway Optic Nerve (ON)

= Axons of ganglion cells in the retina

of the corresponding eye

Outgrowth of diencephalon, so is a

CNS tract & not a true cranial nerve.

Myelinated by oligodendrocytes.

Optic Chiasm (OC)

Located just anterior to pituitary Partial crossing of optic nerve axons

in the OC is essential to binocular

vision

Axons from temporal fields cross

Axons from nasal fields do not

cross Wilbrands knee may be artifact

Note: Reference point = Visual Fields

Pgs. 4 - 5

Retinotopic representation

Central (macular) vision

Peripheral vision

Left visual field Right visual field

Right retinaLeft retina

Left LGN

Tempora

l

Nasal Tempora

l

Nasal

lateral lateralmedial medial

LVFLVF UVFUVF

E.W.

Right visual

cortex

midbrain

Right LGN

Left visual cortex

Left

temporal

retina

Right

temporal

retina

Nasal

retina

Ciliary

ganglion

pretectal

nuclei

cuneus

lingualgyrus

Calcarin

e sulcus

III

III

Upper field

Lower field

VISUAL FIELDS:

Hatched = binocular

Stippled = monocular

Central area = macula

ON

OC

OT


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Optic Tract (OT)

Optic nerve fibers from the optic chiasmcontinue as the optic tract & terminate inthe lateral geniculate nucleus of thalamus.

Each tract contains axons that carry inputfrom the contralateral visual field.

Left OT receives from R. visual field

Right OT receives from the L. visualfield

Pgs. 4 - 5




Peripheral vision



Left LGN

Tempora

l

Nasal Tempora

l

Nasal


LVFLVF UVFUVF

E.W.

Right visual

cortex

midbrain

Right LGN

Left visual cortex

Left

temporal

retina

Right

temporal

retina

Nasal

retina

Ciliary

ganglion

pretectal

nuclei

cuneus

lingualgyrus

III

III

VisualPathwayPost-Chiasmatic portion of the pathway:

From optic tract to visual cortex, each side of the brain

deals with the contralateral visual field.

Upper field

Lower field

VISUAL FIELDS:

Hatched = binocular



ON

OC

OT Lateral Geniculate Nucleus (LGN)

Primary termination of OT fibers

Each LGN receives input from thecontralateral visual field.

OT Projections to pretectum for reflexes


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Peripheral vision

Geniculocalcarine Tract (= optic

radiations)

Axons of LGN neurons travel to primary

visual cortex (Area 17) via the

geniculocalcarine tract located in the

retrolenticular and sublenticular portions

of the internal capsule. Axons from upper visual fields take a

looping course into the temporal lobe on

the way to visual cortex. (=Meyers loop)

Axons from lower visual fields take a

more direct route to visual cortex.

Macular fibers are in an intermediatelocation in the optic radiation.

Pgs. 4 - 5




Left LGN

Tempora

l

Nasal Tempora

l

Nasal


LVFLVF UVFUVF

E.W.

Right visual

cortex

midbrain

Right LGN

Left visual cortex

Left

temporal

retina

Right

temporal

retina

Nasal

retina

Ciliary

ganglion

pretectal

nuclei

cuneus

lingualgyrus

Calcarin

e sulcus

III

III

Meyers

loop

Optic radiation or

geniculocalcarine

tract

VisualPathwayPost-Chiasmatic portion of the pathway:

From optic tract to visual cortex, each side of the brain

deals with the contralateral visual field.

Upper field

Lower field

VISUAL FIELDS:

Hatched = binocular



ON

OC

OT


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VisualPathwayPgs. 4 - 5




Peripheral vision



Left LGN

Tempora

l

Nasal Tempora

l

Nasal


LVFLVF UVFUVF

E.W.

Right visual

cortex

midbrain

Right LGN

Left visual cortex

Left

temporal

retina

Right

temporal

retina

Nasal

retina

Ciliary

ganglion

pretectal

nuclei

cuneus

lingualgyrus

Calcarin

e sulcus

III

III

Meyers

loop

Optic radiation or

geniculocalcarine

tract

Upper field

Lower field

VISUAL FIELDS:

Hatched = binocular



ON

OC

OT

Primary Visual Cortex (Area 17)

Located on either side of & within the

calcarine fissure.

Upper fields project to the lingual gyrus.

Lower fields project to the cuneus.

Macular representation is most caudal in Area

17.

Peripheral field representation is in the rostral

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rds

of Area 17. Lesions of Area 17 result in blindness in the

contralateral visual field.

Association Visual Cortex (Areas 18& 19)

Input from Area 17 & elsewhere

Deals with complex aspects of vision

Lesions of result in visual agnosia.


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Lesions of the Visual Pathway1. Normal visual fields

2. Blindness of the right eye

3. Blindness of right eye + contralateral left upper

quadrantanopia

4. Bitemporal heteronymous hemianopsia

5. Left homonymous hemianopsia

6. Left upper homonymous quadrantanopsia

7. Left homonymous hemianopsia with macular

sparing

RightLeft

Definitions

Strabismus

Diplopia

Amblyopia

Scotoma

Quadrantanopsia - # 3, 6

Hemianopsia - # 4, 5, 7

Heteronymous Defects - # 3, 4

Homonymous Defects - # 5, 6, 7

Congruous Defects - # 5, 6, 7

Incongruous Defects - # 3

Altitudinal Defects - # 6

Masked area = area

of visual loss

Pg. 6

Aka

field

cuts

Fields, not

retinal

quadrants


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Lesions of the Visual Pathway1. Normal visual fields

2. Blindness of the right eye

3. Blindness of right eye + contralateral left upper

quadrantanopia

4. Bitemporal heteronymous hemianopsia

5. Left homonymous hemianopsia

6. Left upper homonymous quadrantanopsia

7. Left homonymous hemianopsia with macular

sparing

RightLeft

Pg. 6


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Right Left

Pupillary Constriction(Miosis)

Nolte 17-38

Afferent limb =

Optic Nerve (SSA)

Efferent limb = Oculomotor Nerve (GVE)

Postganglionic

Preganglionic

Direct

Reflex

Consensual

Reflex

Pg. 7

AKA Pupillary Light Reflex

R fl b li h d if ff t ff t i d d


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Right Left

B

C

Right Left

Right Left

Nolte 17-38

Reflex abolished if afferent or efferent is damaged.Pg. 7

Afferent

defect

Efferentdefect


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Pupillary Dilation(Mydriasis)

Decreased light to pupil

Severe pain

Strong emotional stimulus

ReticularFormation

Reticulospinal

fibers

PreganglionicSympathetic Neurons

in Thoracic Cord (T1-

T2)

(pre-ganglionic

sympathetic)

Dilationof pupil

SuperiorCervical

Ganglion(post-ganglionic

sympathetic)

Cortex,

Thalamus &Hippocampus?

Hypothalamus

(CNS control centerfor AN S)?

Horners Syndrome Pupillary Constriction

Ptosis

Flushed & Dry Skin

Loss of Sympathetics

Lesion can be in CNSor PNS

Deficits ipsilateral to lesion

Pg. 7-8

P 8


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Accommodation (or Near) Reflex

1. Initiated by shift in gaze from far to near.

3. Efferent limb: GSE & GVE of Oculomotor

Optic nerveOptic tractLateral Geniculate NucleusOptic Radiation

Primary Visual CortexAssociation Visual CortexOptic Radiation

Br. of Superior Colliculus

Superior Colliculus

Oculomotor Nuclei

Oculomotor Nerve

Argyll Robertson pupil: Pupillary constriction occurs as part of the

accommodation reflex, but not in response to light.

2. Three components:Ocular convergencePupillary constriction

Lens thickening

4. Afferent limb & Central Connections:

Pg. 8


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The Visual Cortex and Beyond


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Overview of Questions

How can brain damage affect a personsperception?

Are there separate brain areas that determine

our perception of different qualities?


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Figure 4.1 (a) Side view of the visual system, showing the three majorsites: the eye, the lateral geniculate nucleus, and the visual cortex.(b) Visual system showing how some of the nerve fibers from the

retina cross over to the opposite side of the brain at the optic chiasm.


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Pathway from Retina to Cortex

Signals from the retina travel through theoptic nerve to the

Lateral geniculate nucleus (LGN)

Primary visual receiving area in theoccipital lobe (the striate cortex)

And then through two pathways to the

temporal lobe and the parietal lobe


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Visual Areas


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Areas V1 V5

KW 8-17


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Visual

Cortex


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Neurons in Striate CortexEdge detector

End-stopped cells

Respond to:

Moving lines of specific length

Moving corners or angles No response to:

Stimuli that are too long


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Feature Detectors

Neurons that fire to specific features of astimulus

Pathway away from retina shows neurons

that fire to more complex stimuli Cells that are feature detectors:

Simple cortical cell

Complex cortical cell

End-stopped cortical cell


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Table 4.1 Properties of cortical neurons


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Figure 4.17 (a) Red and blue areas show the extent of stimuli that were presented while a person was in anfMRI scanner. (b) Red and blue indicates areas of the brain activated by the stimulation in (a). (From

Dougherty et al., 2003.)

Fovea

Periphery

VisionVisualized

With

FMRI


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Brain Imaging Techniques - fMRI

Functional magnetic resonance imaging (fMRI)

Hemoglobin carries oxygen and contains a ferrous

molecule that is magnetic

Brain activity takes up oxygen, which makes the

hemoglobin more magnetic

fMRI determines activity of areas of the brain by

detecting changes in magnetic response of

hemoglobin

Subtraction technique is used like in PET


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Figure 4.14 The magnification factor in the visual system: The small area of the fovea is represented by a

large area on the visual cortex.


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Maps and Columns in the Striate Cortex

Cortical magnification factor

Fovea has more cortical space than

expected

Fovea accounts for .01% of retina Signals from fovea account for 8% to

10% of the visual cortex

This provides extra processing for high-acuity tasks.


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Other Cortical Areas

Vision begins to processed by V1-V5

Then goes to other lobes of the brain for

further processing.

What we have seen. Object identification.

Where we have it. Locating object in world.


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Figure 4.27 The monkey cortex, showing the whatand the wherepathways. The wherepathway is also called the howpathway. (From

Mishkin, Ungerleider, & Macko, 1983.)


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What and Where (How) Pathways

Where pathway may actually be Howpathway

Dorsal stream shows function for bothlocation and for action.

Evidence from neuropsychology

Single dissociations: two functionsinvolve different mechanisms

Double dissociations: two functionsinvolve different mechanisms andoperate independently


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Table 4.2 A double dissociation


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What and How Pathways - Further Evidence

Rod and frame illusion Observers perform two tasks: matching

and grasping

Matching task involves ventral (what)pathway

Grasping task involves dorsal (how)pathway

Results show that the frame orientationaffects the matching task but not thegrasping task.


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Figure 4.30 (a) Rodand frame illusion.

Both small lines areoriented vertically.(b) Matching taskand results. (c)Grasping task andresults.


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Modularity: Structures for Faces, Places,

and Bodies

Module - a brain structure that processesinformation about specific stimuli

Inferotemporal (IT) cortex in monkeys

Responds best to faces with littleresponse to non-face stimuli

Temporal lobe damage in humans results

in prosopagnosia.


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Figure 4.32 (a) Monkey brain showing location of theinferotemporal (IT) cortex. (b) Human brain showinglocation of the fusiform face area (FFA), which is locatedunder the temporal lobe.


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Monkey

Face

Cells


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Evolution and Plasticity: Neural

Specialization

Evolution is partially responsible for shapingsensory responses:

Newborn monkeys respond to direction of

movement and depth of objects Babies prefer looking at pictures of

assembled parts of faces

Thus hardwiring of neurons plays a part

in sensory systems


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Margaret Thatcher Illusion


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Lect2 Vision 1