Visual Processing in the Brain and Damage to the

Visual Brain

Developed by the SKI-HI Institute

Utah State University Spring 2011

For use in VIISATraining

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The Visual Brain

• The brain devotes more territory to vision than all other senses combined (40%)

• There are 32 distinct areas in each hemisphere of the brain involved in visual processing.

Information Leaving the Retina

• Retina: changes light energy to neural signals and performs computations on those signals, processing

• Axons leaving the eye are heterogeneous, carrying different types of information:

spatial and depth

motion

color

lines and form• Some go to subcortical areas of the

brain, leaving the main optic path before the LGN

• Most continue to the LGN and on to the Visual Cortex 3

Key Subcortical Functions: SCN

• Controls sleep-wake cycle

• Production and release

of some hormones

• Changing time zones,

neurons in SCN need

time to retrain to new

light-dark cycle

• Implications for sleep problems in children who are blind

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The Accessory Optic System (AOS)

• 3 separate nuclei in the brainstem

• Project to the cerebellum and spinal cord

• Play critical role along with vestibular and proprioceptive systems in:

-visual stabilization

-postural control

-regulating locomotion

and heading 5

Other Pathway Destinations• Superior Colliculus:

Initiation and control of orienting movements of eyes, head and body to things in the peripheral fields and fixation on them

• Some control pupil size

• Some in brainstem to control eye muscles

• Some in spinal column to control muscles in neck, trunk and limbs

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• Improved head and trunk control also often leads to

improved visual functioning

Lateral Geniculate Nucleus and V1

• Projects to the cerebral cortex

• Almost all the fibers terminate in the primary visual cortex or V1 area

• All subcortical areas not only receive information from the eye but also the V1 area

• They are also connected with each other as well as hearing and touch

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Frontal Lobe

Parietal Lobe

Dorsal Stream

Ventral Stream

Temporal Lobe

Dr. Lea HyvarinenHelsinki, Finland, 2004

Ventral and Dorsal Streams

Visual Cortex

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Why do we need these two visual systems?

Visual Perception• Helps us make sense out of the outside world• Allows us to create representations of it that can be filed

away for future reference

Guiding Action• Requires accurate information about actual size, location

and motion• Has to be coded in the absolute metrics of the real world• Has to available in real time

Ventral StreamWhat?

Recognition of . . .

facial expressions

colors & shapes

faces

letters and words

animals

objects

Recognition of landmarks for stored routes so we can remember how to get home from work.

yellowyellow

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Studying Brain Injury in the Old and the Young

• We are learning a lot about how the visual brain works from adults who have suffered brain injuries from strokes, trauma, oxygen deprivation, etc.

• They are able to talk about what and how they see in a way that young children with brain injury can’t.

• Brain injury to young children may affect the visual brain in similar ways.

• But in the very young child, brain plasticity may help the visual brain rewire to some degree around the lesions.

• Depending on where, when or how much damage occurred, visual functioning may vary.

• This is an exciting, emerging field of study.

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Dee• Case discussed in “Sight Unseen” by

Goodale and Milner

• Suffered carbon monoxide poisoning

• A few days after the injury, she could walk, talk, hear, but not see.

• Over time, regained conscious sight, but sight without form. She could not see edges or outlines of objects

• Objects had to have a distinctive color, smell or texture for her to recognize them.

• When she touched the object, she could then recognize it.

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Dee’s Dorsal Stream Functioning

• She could reach out and grasp a pencil accurately and use it.

• She could use her hands well for many daily tasks.

• She could get around her environment well.

• She could hike over difficult terrain

Vision for perception was profoundly

affected and vision for action

unscathed.lh3.ggpht.com

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Dee’s Ventral Stream Function(15 years later)

• Could not recognize short printed words on a page• Could not recognize faces or drawings and photos of

every day objects• Trouble separating object from background: knife and fork

next to each other were too similar and looked like a blob• Difficulty naming geometric shapes, even when on

contrasting background; but when felt, she could name them

• Could not copy simple pictures, but could draw from memory

• Damage to her ventral stream had a profound impact on her visual functioning

Damage Can Be Specific to a Function

For example:

Can not recognize a familiar face. . . but can see it, reach for it, and

touch the face

Can match faces. . . but not be able to name who they are

Acuity can even be normal

Dr. Lea Hyvärinen,Helsinki, Finland, 2004

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Facial Recognition

Ways children compensate for loss of face recognition:

May recognize people by their voice.

May always ask who they are.

If have problems with auditory recognition, may use other cues instead, for example:

color of shoes smell.Let the child use whatever compensatory technique

works for them.

Sometimes, may need to teach slower child how to compensate.

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Getting Lost in His Neighborhood

• Little boy would get lost in his own neighborhood

• Could not find best friend’s house even after repeated walks to it

• Was not able to recognize, use, remember landmarks to help him find his way to and from

• A ventral stream function• He had good acuity• Looking at alternative supports such

as written directions for him to follow to get to places

www.pbase.com

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Dorsal StreamWhere?

eye-hand, eye-foot coordination motion perception

orientation in space

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Problems with Motion Perception

• Rare and called akinetopsia• See stationary objects quite well• When object moves relatively quickly, they lose it

Woman who:• Difficulty pouring coffee into cup because she could not

see liquid rising• Saw movement as a series of snapshots• Daily scenes looked like jerky, strobe-like movements

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Problems with Motion Perception

traffic

Uncomfortable around . . .

fast moving small animals playgrounds

PEPI, The Dalmatian in Motion by Lea-Test Ltd. Copyright 2001 30

Perception of Objects in Space

get lost easily

If damaged, these children may . . .

have difficulty with accurate reach

have difficulty with eye-hand/ eye-foot coordination (stepping on/off curbs, across sidewalk cracks, or changes in floor surfaces)

difficulty in crowded situations

Dr. Lea Hyvärinen,Helsinki, Finland, 2004 31

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Multiple Visual Tasks

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Infants/Toddlers: One Thing at a Time

• Visually being aware of multiple things takes time to develop and mature

• Infants and toddlers focus on one thing at a time, and

may ignore the rest of the world• For some children, this skills may be delayed, so they

may trip over, bump into things, fall off a curb when

focused on something they see at a distance, ignoring

the obstacles along the way• In the absence of an ocular disorder or CVI, this

corrected itself over time, and the children were able to

handle multiple pieces of information.

Visual array may need to be simplified

Damage to the Parietal Lobe

Child may need to use a cane

Child may need to move closer to block out background in order to simplify the visual array and focus on the single most important item

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Visual array may need to be simplified

Damage to the Parietal Lobe

Child may need to use a cane

Child may need to move closer to block out background in order to simplify the visual array and focus on the single most important item

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Difficulty Scanning and Reading

Difficulty followingmovements

Difficulty scanningthe environment

A lot of print on the page cannotbe seen at once

Moving head and eyes accurately to read is hard

Present smallnumbers of wordsat same time,enlarged, showthem sequentially

How are you?

H o w a r e y o u ?

H O W

A R E

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Specific Problems

Lesions to parietal lobe can result

From brain bleeds, strokes, etc.

Specific visual problems:• Loss of ability to direct the arm

toward a visual target that they can look at

• Reach to a target, but cannot direct gaze to it

• Can see and reach to a target but not adjust grasp to it

images.teamsugar.com

Frontal Lobe

Parietal Lobe

Role of Other Lobes in Vision

• Frontal lobe executes command functions to visually attend to objects and to turn eyes and head in anticipation

• Parietal lobe works closely with frontal lobe and motor cortex to do this

• Damage to frontal lobe can make it hard for child to decide what is most important to focus on; everything catches their attention

• Simply and structure the environment

Motor Area

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Dr. Lea Hyvärinen,Helsinki, Finland, 2004

Reticular Activating System

Reticular activating system

Arousal and

Wakeful-ness

OT with SItraining canprovide ideas for ways toalert:MovementMassageMusicJoint com-pression

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Organizing the Child for Using Vision

Reduce amount of incoming stimuli for child who is easily overwhelmed.

Help organize the visual system with massage, joint compressions, gentle movement, soothing sounds.

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Ways Visual Information is Handled in the Brain

• The reflexive or primitive visual system

• The higher visual system --Where --What

•Both of these high level visual systems can be damagedto varying degrees with a wide array of affects seen.

• Each child shows a unique combination of features

• When primary visual cortex and processing centers are damaged, vision problems occur (CVI) 43

Damage to the Brain and

Vision Impairment

• Focal damage to the visual brain leads to specific visual difficulties

• Diffuse damage affects all aspects of brain function, including visual processing

• Simple problems affecting visual acuity, field and contrast are easy to identify

• Abnormal development of or injury to the optic radiations, visual cortex and visual processing areas (ventral/dorsal streams) result in vision problems

• The role of perceptual and cognitive visual dysfunction in many other disabilities such as intellectual, autism, cerebral palsy, may not be recognized or understood.

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Acquired Neurological Injury:Hypoxic-Ischemic

• Brain needs glucose and oxygen.• When deprived of one of these, potential

for long term brain dysfunction exists. • Asphyxia is lack of oxygen. Too little

oxygen (hypoxia) disrupts regulation of

blood supply to the brain, creating too

little blood flow (ischemia). • Severity and duration of episode

determines extent of damage• Organ damage, CP, seizures, hearing loss, CVI• When causes irritation to brain-encephalopathy• Numerous causes (e.g., PP, twin-to-twin, maternal diabetes or infection)• Can occur in utero, during birth, after birth; mostly in preterm newborns

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Periventricular Leucomalacia

• Most common neurological lesion in the preterm infant (24-34 weeks)

• White matter damage in the watershed zones of the immature brain

• Due to hypoxic-ischemic event-brief or profound impairment of blood flow to the area so no oxygen; preterm or perinatal-different

effects• Affects superior part of optic radiations

(result is lower field loss); subcortical

white matter that serves vision and association

areas (processing); oculomotor nerve damage• Wide range of visual and cognitive functioning• Field losses, visual/spatial problems, crowding

interpreting complex visual patterns.

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Focal Brain Lesions• Includes such things as: arterial or venous stroke, intracranial

hemorrhage, focal tumor• Nature and range of visual impairment depends on the location and

extent of the lesions• At first, visual attending is poor, but usually acuity ends up OK, but

there is field loss• Unilateral lesion behind optic chiasm may lead to homonymous

field defect• Acuity is impaired when lesion is extensive or bilateral• Eyes move to target in blind hemifield, overshoot, then correct with

microsaccades• Need to learn to scan• Central loss due to stroke, turn eyes away from field loss• Severe stroke can also lead to CP, seizures, delays

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Intraventricular Hemorrhage (IVH)• Low birthweight premature babies may suffer brain

bleeds in and around the ventricles• Germinal matrix is just outside the ventricles;

incubator for brain cell production• In preterm, this area abundant in fragile blood

vessels• Events causing too little or too much blood flow to

area can lead to a bleed• Bleeds graded from I to IV (worst)• Optic radiations pass by and around the lateral

ventricles• These bleeds can damage the optic radiations,

resulting in vision loss• Severity of vision loss depends on the extent of the

bleed, treatment, other medical issues, etc.• Grade III-IV bleeds can lead to CVI,

CP, hydrocephalus, delays

Lateral Ventricle

Lateral Ventricle(other views)

OpticRadiations

Grade III Bleedin the LateralVentricles

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Traumatic Brain Injury

© VictorPowell.com

• Shaken baby or accidents• Lead to: hemorrhaging, diffuse damage to axons,

increased pressure in brain then hypoxic-ischemic events

• Damage can be focal, multifocal or diffuse• The brain injury can result in CVI• At first, visual recovery may be rapid, but not

complete• Optic nerve atrophy seen later, poor visual

prognosis

Infections•Occur before or after birth•TORCH infections passed from mother to fetus (CMV, Herpes, rubella, toxo)•Result can be CP, seizures, CVI•Some ocular conditions such as cataracts can occur with these•CMV and meningitis can lead to vision and hearing loss•Vision loss can be CVI, optic nerve atrophy or nystagmus

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Other•Neonatal Hypoglycemia

-if not treated, brain injury can

occur; results in poor cognition,

motor problems, epilepsy

•High Bilirubin

-Chronically high; leads to hearing

loss, abnormal swallow and

speech, visual gaze problems

•Metabolic Disorders

-mitochondrial, lysosomal and peri-

oxisomal

-CVI in context of neurlogical

deterioration along with many

other problems

Brain Malformations

• Alterations in normal progression of brain development has neurological consequences

• Include things like:

-Spina Bifida, Dandy Walker Syndrome

-microcephaly, lissencephaly,

schissencephaly, hydrocephalus

-agenesis of corpus calosum• Result from chromosomal disorder,

infections, or idiopathic• Mild to severe developmental outcome• Present early with poor visual attention• May also see optic nerve anomalies,

CVI, nystagmus, seizures

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Lissencephaly

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Hydrocephalus• Increased fluid in the ventricles or water

spaces of the brain

• Put pressure on optic nerve fibers; vision

transient or episodic due to vascular

dysfunction or hypertension in brain

• Prolonged high pressure causes

permanent damage

• Putting in shunt to drain fluid soon enough can minimize the damage

• Decreased visual functioning can be a

sign of shunt failure

• Acuity problems, strabismus, field loss, visual

perceptual problems

Optic nerve head in backof the eye of 2 year old

child with hydrocephaluswww.nature.com/

Child with Shuntwww.mps1disease.com

Chromosomal Disorders

•Trisomy 13 and 18•Common eye problems:

-microphthalmia

-coloboma

-abnormal optic nerve and eye

structures

-CVI

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Epilepsy

•Uncontrolled seizures, lead

to poor acuity and attention•Exclude diagnosis of infantile

spasms with infants who have

unexplained vision loss