Strokes Evidence

The 2 Hemispheres of the Brain • right

• left

• emotional • holistic • intuitive

• logical • calculating • linguistic

• right

• left

– optimistic – unemotional – un-noticing of serious injury and disability

– pessimistic – overly emotional – overly noticing of even nonserious problems

• anosognosia

Really, really, really oversimplified…… oversimplified…….. Not complete garbage…… garbage……..

Lateralized Brain Functions Lateralized = one hemisphere “controls” controls” task processing • language - left (Broca and Wernicke’s) – left-handers - sometime right - language

Localized versus Lateralized Localized = contiguous portion of the brain controls task • amnesia - selective memory loss – patient GR who forgets identity for years – recovers it on operating table (Schacter)

• aperceptive agnosia • faces - right hemisphere • visual motor tasks - right

– good vision, no ability to recognize shapes, forms

• associative agnosia – good vision, good shape, object recognition problems – Man who mistook his wife for a hat (Sacks) • recognition of a glove

• dyscalculia – cannot do simple caluculations – left angular gyrus (Ramachandran)

• prosopagnosia - selective memory loss – cannot recognize faces

• Capgras Syndrome • aphasia – Broca’s - cannot speak (tan) - left frontal – Wermicke’s aphasia - can’t undertand - left temporal

• alexia

– think someone you love has been replaced by an imposter – no other signs of dementia

Let’ Let’s be critical ….are these disorders evidence for localization?

– cannot read

• agraphia – cannot write

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A few ways to move information across • cerebral hemispheres - corpus callosum • vision - optic chiasm

Cortex - Corpus Collosum • bridge of 80 million fibers • split brain patients

• audition - a subcortical mess! • sensory motor - spinal cord • emotion - anterior commissure

Vision - Optic Chiasm • right hemifield- left hemisphere • left hemifield - right hemisphere

Sensory Motor Audition Subcortical Mess! pain, temperature

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Emotion - Anterior Commissure • primates - some vision also touch, vibration

Physiological Difference • Right

• Left

– more white matter

– more gray matter

– – – –

– – – –

mylinated axons... more holistic axons longer…. talk more broadly...

Split Brain Patient

cell bodies more local axons shorter less extensive connectivity

What the experiments can tell us

• • • • •

corpus collosum severed severe epilepsy….tumors generally normal…. but under the right circumstances clever experiments….

Question 1 Visual, Verbal, and Tactile Coordination

• How the hemispheres communicate visual, verbal, and tactile information • How they communicate emotion

• Roger Sperry (Nobel Prize) • M. Gazzaniga

• split brain patients • How they coordinate motor activity • How they exist somewhat independently...

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Part 2 Part 1 - cup flashed to left hemisphere (via right visual field) - experimenter - “what did you see?” see?” - patient - “a cup” cup”

NORMAL - visual signal passed through optic chiasm to left hemisphere - patient responds “cup” cup”

Part 3

- spoon flashed to right hemisphere (via the left visual field) - experimenter - “what did you see?” see?” - patient - “nothing” nothing” - visual signal passed through optic chiasm to right hemisphere - left hemisphere… hemisphere….has no knowledge of the visual signal - patient responds “nothing” nothing” - did the patient “see” see” the spoon? - yes… yes…..

Question 2 - Emotion Processing

- spoon flashed to right hemisphere (again) - experimenter - “what did you see?” see?” - patient - “nothing” nothing” - put patient’ patient’s left hand in the bag… bag…. - Experimenter - “Find the object you saw” saw” - Patient - pulls a spoon out of a bag with a bunch of objects

• M. Gazzaniga & LeDoux (78)

• split brain patient • special patient who could read a bit from both hemispheres (PS)

REASON - picture of the spoon is in the right hemiphere - left side of the body is controlled by the sensory-motor cortex (parietal) in the right hemisphere!

Part 1

Part 2

- patient saw emotionally charged words - words presented to the left hemisphere

- patient saw emotionally charged words - words presented to the right hemisphere

Devil

Devil

- Experimenter - “Was the word good or bad?” bad?” - Patient - “bad” bad”

- Experimenter - “Was the word good or bad?” bad?” - Patient - “bad” bad”

Experimenter - “What was the word?” word?” - Patient - “devil” devil”

- Experimenter - “What was the word?” word?” - Patient - “what word?” word?”

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Question 2 - Emotion processing

Conclusion

• M. Gazzaniga & LeDoux (78) Emotional stimuli “make it across” across” even without the corpus collosum

• split brain patient

How?

Anterior Commissure? Commissure?

- patient saw emotionally upsetting vignettes to the right hemisphere… hemisphere…... - patient - developed a fear of Gazzaniga - no ability to explain why!

-episodic experience giving rise to emotion -inaccessible by language

Question 3 Systematic Coordination of Motor Activity • Alien hand phenomenon – Kurt Goldstein (1930’s) - well-known neurologist – – – –

case study- middle aged woman normal except….. would try to strangle herself with her left hand right hand would act to fight off the left hand

-emotion itself -accessible to language

• explanation – autopsy revealed a corpus callosum lesion – motor coordination of the left side of the body (i.e., left hand) – right hemisphere (more emotional) • latent suicide tendencies instruct the left hand – left hemisphere - unaware of right’s “intentions” • fights off the attack

Implication about will and self????

Are there two of us????

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Question 4 Independent Existence

Case 2 - dressing example… example…. - right brain more expressive than left - left brain more conservative

• case of young man • asked what he would like to do with his life • left hemisphere responds differently than right – architect – race car driver…...

Abilities/Interpretation

Left-hemisphere interpreter • Gazzaniga & LeDoux

• the left-hemisphere interpreter • picture matching task • the right-hemisphere statistician

– – – –

a picture to left hemisphere - chicken a picture to right hemisphere - snow storm match board available to both responses made with hands

Results • left hand matches right hemisphere picture – shovel for snow storm

• right hand matches left hemisphere picture – chicken foot for chicken

• subject asked… – why did your left hand pick the shovel?

• left hemisphere makes up an answer!

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Right-hemisphere statistician • • • • • • • •

Wolford study light 80% on right light 20% on left we distribute responses to match probabilities 68% correct Rats “maximize” and push right 100% 80% correct right hemisphere - uses rat, statistician strategy

Things the mind/brain does… • Getting information about the outside world to the inside and into a form in which it can be used….

What is perception? • definition - process by which physical energy from the environment impinging on the senses is converted into electrochemical energy by the senses and processed by the brain for the purpose of effective and adaptive interaction with the world

A complete understanding….. • • • • •

neuroanatomy neurophysiology psychology computational problem philosophy

Neurophysiology

Neuroanatomy • • • •

“hardware” or “wetware” - neural substrate kinds of cells connectivity between cells wiring of the relevant brain areas

• receptive fields of cells in relevant brain regions • questions – – – –

organization of processing parallel versus serial processes hierarchical special purpose

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Computational Problem

Psychology • What can we perceive?

• What is the problem?

• What do we do well?

• What is the information available to solve the problem?

• What do we do badly? • What do we do with perception…tasks we solve?

• How can the information be quantified and used to solve the problem? • Can this give insight into biological and/ or psychological solutions to the problem?

Vision

Steps of Perceptions • light Sense

Energy

Organ

Transduction Brain

Vision

Light

Eyes

Rods/cones

Occipital

Audition

Sound pressure

Ears

Hair cells

Temporal

Touch

Mechanical /temperature

Body

Lots

Parietal

Gustation Chemical

Tongue Taste buds

Parietal

Olfaction Chemical

Nose

Olfactory bulb, etc.

Hair cells

• emitted versus reflected light

– dimensions • intensity - photons per unit area per unit time • wavelength composition – color, hue – spectra

• saturation - percentage of white light

• emitted versus reflected light illuminant

sensor reflector

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The pattern of light on the retinae is:

complex function of: illuminant reflectance properties of the object viewer position

Philosophy • Marr (1982) Vision – What is the purpose of vision? – create a 3D map of the world in the brain

Vision is the solution - what is the problem?

• Gibson (1966) – vision is for action – navigation, manipulation, exploration

What is the purpose of the eye?

Gregory (1997).

• to get a good image….

Eye and Brain.

• What is a good image?

Tradeoff between

– focus - resolution – contrast - light level, not too much, not too little – light sensitivity - detection

resolution - focus light level - detection

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Gregory (1997). Eye and Brain.

The right balance depends on the environmental constraints and tasks of the creature … What about us? Gregory (1997). Eye and Brain.

The eye is like a camera, but... • It moves ……not randomly….

Gregory (1997).

Gregory (1997).

Eye and Brain.

Eye and Brain.

Kinds of eye movements

The eye is like a camera, but...

• vergence – convergence, divergence • saccades – ballistic movements, scan, reading

• there are two of them • binocluar vision • stereopsis

• pursuit, tracking • optokinetic nystagmus • jitter

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Parts of the eye in functional terms

Parts of the eye in functional terms Focus - refraction of light -17 mm focal length

Light level

cornea -shape - 42 diopters

Pupil - quantity of light - emotional

lens - changeable shape - fine tuning - accomodation - 15-20 diopters

Pigment epithelium - absorbs excess tapetum - scatters excess

Landmarks on the Retinae • optic disc – optic nerve exits the retina – blind spot - demo

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• fovea – point of highest acuity

Receptor • rods • “black and white” • high light sensitivity – too sensitive to light to operate during daylight

• absorption spectrum – peak 500 nanometers – green

• cones • color vision – 3 kinds • L wavelength R, 550 • M wavelength G, 535 • S wavelength B, 419

• low light sensitivity – daylight – not useful at night

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2 Visual systems • scotopic - rod vision • photopic - cone vision • mesopic - rod/cone vision

rods and cones horizontal cells bipolar cells amacrine cells ganglion cells optic nerve axons of ganglion cells

Circularly Symmetric Receptive Fields

Receptive fields as convolution operators • Simple picture

-

+

-+-

-

-

On-center off-surround

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+ -- -

+

+

+

Off-center on-surround

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Simple Edge detector • Simple picture as 2D array of pixels

1 -1

• Convolution operator -> edge detector

Pixel = 20

Pixel = 100

100 100 20 20 1

Simple Edge detector

Result

1 -1

• Convolution operator -> edge detector- “mask”

-1

1 -1

• Convolution operator -> edge detector- “mask”

100 100 20 20 20*1 + 100*(-1) = -80

1 -1

Pixel 1 = 100*1 + 100*(-1) = 0

Pixel 2 = 100*1 + 20*(-1) = 80

Pixel 3 = 20*1 + 20*(-1) = 0

100

w1x1 w2x2

W1=1

Swixi

All receptive fields work this way! 0

100

• Only the complexity and dimensionality of the operators will change

w1x1 w2x2

Pixel 2 = 100*1 + 20*(-1) = 80

Pixel 3 = 20*1 + 20*(-1) = 0

W2=-1 axon

Pixel 1 = 100*1 + 100*(-1) = 0

Swixi

axon

80

20 w1x1 20

w2x2

Swixi

axon

0

13

+

-

-

-

1 -1

1 -1

1 0 0 -1

14

0 1 -1 0

+ -

+

+ -

-

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