Announcements http://www.umich.edu/~psycours/345/

Announcements http://www.umich.edu/~psycours/345/

Study Guide available on web by 8 PM Study Guide available on web by 8 PM tonighttonight

Quiz next week for first hour of class.Quiz next week for first hour of class. Multiple choice, fills in, identificationsMultiple choice, fills in, identifications Bring pencils for scantrons Bring pencils for scantrons

Last LectureLast Lecture

Projections maps and Projections maps and the homuculithe homuculi

Organization of the Organization of the Visual SystemVisual System

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This LectureThis Lecture

Organization of the Organization of the Visual System Visual System continuedcontinued

BlindsightBlindsight what it is; how it ‘s what it is; how it ‘s

studied; what it tells us studied; what it tells us about human visual about human visual information processing.information processing.

What/Where pathwaysWhat/Where pathways Their discovery, their Their discovery, their

neural origins, their neural origins, their manifestations in humansmanifestations in humans

Sensitive areas are “magnified”Sensitive areas are “magnified”

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Field of View

Cortical Map of Visual Field

Receptive Field:

the region of the sensory surface that makes a cell fire.

Cortical Magnification• Each neuron in area 17 has a retinal receptive field• More neurons have foveal receptive fields

Pathway from Eye to BrainPathway from Eye to Brain

Geniculo-Striate pathwayGeniculo-Striate pathway Optic nerve carries Optic nerve carries

signals from retina.signals from retina. Decussation at optic Decussation at optic

chiasm (optic tract)chiasm (optic tract) Synapse at LGN of Synapse at LGN of

thalamusthalamus Optic radiations to Optic radiations to

occipital lobe occipital lobe AREA 17; Striate CortexAREA 17; Striate Cortex

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The connectionsThe connections

Left EyeLeft Eye Nasal hemiretina- LVF- Nasal hemiretina- LVF-

projects to right projects to right hemispherehemisphere

Temporal hemiretina- RVF- Temporal hemiretina- RVF- projects to left hemisphereprojects to left hemisphere

To cross at optic chiasm

uncrossed uncrossed

Right EyeRight Eye Nasal hemiretina- RVF- Nasal hemiretina- RVF-

projects to left hemisphereprojects to left hemisphere Temporal hemiretina- LVF- Temporal hemiretina- LVF-

projects to right projects to right hemispherehemisphere

nasal

LVF input to RH

RVF input to LH

Vision requires cortex… or does it?Vision requires cortex… or does it?

Reports of residual vision in animals with striate Reports of residual vision in animals with striate

lesionslesions:: Recovery after experimental field defectsRecovery after experimental field defects

spared light/dark discriminationspared light/dark discrimination spared localization abilitiesspared localization abilities

Implication: Other structures (tectum) can Implication: Other structures (tectum) can compensate for striate function.compensate for striate function.

LGN StriateextraStriate

LORE of neurology until the early 70's...

Re-Evaluate vision in human scotomas:

Poppel, Held & Frost (1973)Poppel, Held & Frost (1973).. Residual Residual visual function after brain wounds visual function after brain wounds involving the central visual pathways in involving the central visual pathways in man. man. NatureNature..

Task:Task: light flashed in scotoma light flashed in scotoma Patient looks at (saccades) to flash Patient looks at (saccades) to flash

locationlocation NOTE: Patient protests: “How NOTE: Patient protests: “How

can I look at something I can't can I look at something I can't

see?" see?" Experimenter: Experimenter: GUESS!GUESS!

ResultsResults:: Saccadic endpoint related to target Saccadic endpoint related to target

locationlocation Text notes case D.B. (Weiskrantz)Text notes case D.B. (Weiskrantz)

0

10

20

30

40

5 10 20 30

Saccade loc

TARGET LOC.

Why Does Blind Sight Occur?Why Does Blind Sight Occur?Why Does Blind Sight Occur?Why Does Blind Sight Occur?

One theory (non-striate hypothesis):One theory (non-striate hypothesis): Due to non geniculo-striate pathwaysDue to non geniculo-striate pathways

Retinotectal pathway --> direct route for saccadic eye Retinotectal pathway --> direct route for saccadic eye movement control.movement control.

Tecto-pulvinar-extrastriate --> indirect route for manual Tecto-pulvinar-extrastriate --> indirect route for manual and guessing responses.and guessing responses.

LGN StriateextraStriate

S.C.tectopulvinar pathway

PulvinarRetinotectalpathway

Alternative to Nonstriate Hypothesis: Cortical (Striate) IslandsAlternative to Nonstriate Hypothesis: Cortical (Striate) Islands

Fendrich, et al. (1992).Fendrich, et al. (1992). detailed perimetry, detailed perimetry,

retinal stabilizationretinal stabilization revealed islands of revealed islands of

vision in scotomavision in scotoma Implications:Implications:

Spared tissue in Area Spared tissue in Area 17 can explain residual 17 can explain residual vision.vision.

Colliculus may not Colliculus may not mediate all blindsightmediate all blindsight

WHY is consciousness lacking?WHY is consciousness lacking?

Two possibilitiesTwo possibilities Non striate theory: primitive SC Non striate theory: primitive SC

circuitry SC is inadequate for circuitry SC is inadequate for "awareness"."awareness". Cortex necessary for awarenessCortex necessary for awareness

Both theories:Both theories: The weak visual signal The weak visual signal is below threshold for consciousness.is below threshold for consciousness. non-striate theory- SC only gets non-striate theory- SC only gets

weak retinal input.weak retinal input. Cortical Islands- tissue fragments Cortical Islands- tissue fragments

are insufficient for consciousness--are insufficient for consciousness--NOTE: cortex does not equal NOTE: cortex does not equal consciousness.consciousness.

Lessons from BlindsightLessons from Blindsight

Implicit vs Explicit (conscious) Knowledge.Implicit vs Explicit (conscious) Knowledge. Parallel operationsParallel operations Yield products (representations) for different Yield products (representations) for different

behaviorsbehaviors

Human residual visual is “nonfunctional” Human residual visual is “nonfunctional” compared to animals.compared to animals. humans "residual" capacities seen only with humans "residual" capacities seen only with

experimental methods.experimental methods. nonhuman species may depend more on tectumnonhuman species may depend more on tectum Encephalization of visual (WHAT & WHERE) Encephalization of visual (WHAT & WHERE)

function in primates and humans.function in primates and humans.

Announcements http://www.umich.edu/~psycours/345/

Announcements http://www.umich.edu/~psycours/345/

Study Guide available on web by 8 PM Study Guide available on web by 8 PM tonighttonight

Quiz next week for first hour of class.Quiz next week for first hour of class. Multiple choice, fills in, identificationsMultiple choice, fills in, identifications Bring pencils for scantrons Bring pencils for scantrons

The What and Where PathwaysThe What and Where Pathways

The Ungerleider & Mishkin (1982) ExperimentThe Ungerleider & Mishkin (1982) ExperimentThe Ungerleider & Mishkin (1982) ExperimentThe Ungerleider & Mishkin (1982) Experiment

Task 1: Task 1:

Object discriminationObject discrimination study an object study an object select the familiar object* select the familiar object*

(reward) (reward)

parietal lesions parietal lesions impair LANDMARK TASKimpair LANDMARK TASK

temporal lesions temporal lesions impair OBJECT TASKimpair OBJECT TASK

Task 2:Task 2:

Landmark discriminationLandmark discrimination• select foodwell closest to select foodwell closest to the TOWERthe TOWER

Conclusion: Conclusion:

VENTRAL stream processes identity informationVENTRAL stream processes identity information DORSAL stream processes spatial informationDORSAL stream processes spatial information

Logical basis for this inference:Logical basis for this inference:

1) Focal parietal lesion --> selective deficit, 1) Focal parietal lesion --> selective deficit, dissociation: “where” impaired, “what” intactdissociation: “where” impaired, “what” intact

2) Focal temporal lesion --> selective deficit, 2) Focal temporal lesion --> selective deficit, dissociation: “what” impaired, “where” intactdissociation: “what” impaired, “where” intact

DOUBLE DISSOCIATIONDOUBLE DISSOCIATION

Inadequacy of a single dissociationInadequacy of a single dissociation

Consider the following hypothetical Consider the following hypothetical outcome:outcome:

Parietal & Temporal lesions impair the Parietal & Temporal lesions impair the landmark task, but neither impaired landmark task, but neither impaired the object taskthe object task

What does this result mean?What does this result mean? A) both brain areas contribute to A) both brain areas contribute to

spatial processing?spatial processing? B) the tasks differ in difficulty?B) the tasks differ in difficulty?

Double Dissociation: Double Dissociation:

Experimental Experimental strategy strategy 2 brain areas (X,Y) 2 brain areas (X,Y) 2 different tests 2 different tests

(T1,T2). (T1,T2).

ResultResult Lesion of X Lesion of X

impairs T1 not T2impairs T1 not T2 Lesion of Y Lesion of Y

impairs T2 not T1impairs T2 not T1

Locus X Locus Y

11

22

DOUBLE DISSOCIATION

PE

RC

EN

T C

OR

RE

CT TASK

BRAIN REGION

Double Dissociation Logic AppliedDouble Dissociation Logic Applied

Locus X Locus Y

11

22

DOUBLE DISSOCIATION

PE

RC

EN

T C

OR

RE

CT TASK

What/Where DISSOCIATION

Temporal Parietal

ObjectObject

SpatialSpatial

PE

RC

EN

T C

OR

RE

CT

TASK

Why do these separate pathways exist?

Different functions:Different functions: NEED special purpose machinery.NEED special purpose machinery. have different computational have different computational

demands.demands. require different types of information.require different types of information.

How does the input to these How does the input to these pathways differ?pathways differ?RETURN to the Retina:RETURN to the Retina:

1. 1. photoreceptors (rods and cones) photoreceptors (rods and cones) perform transductionperform transduction

2. Signals sent to RETINAL GANGLION 2. Signals sent to RETINAL GANGLION CELLS (RG).CELLS (RG).

3. Convergence: many photoreceptors 3. Convergence: many photoreceptors

--> one RG cell--> one RG cell

M and P Retinal Ganglion Cells

RG Cells are not just light detectors.RG Cells are not just light detectors. Cells classified by what "turns them on"Cells classified by what "turns them on" receptive field properties of cellsreceptive field properties of cells

M cellsM cells

a) project to a) project to Magnocellular Magnocellular layers of LGNlayers of LGN

b) dominant in DORSAL/WHERE streamb) dominant in DORSAL/WHERE stream

c) also go to SCc) also go to SC

d) fast conducting, colorblind, low acuityd) fast conducting, colorblind, low acuity P cellsP cells

a) project to a) project to ParvocellularParvocellular layers of LGN layers of LGN

b) dominant in VENTRAL/WHAT streamb) dominant in VENTRAL/WHAT stream

c) slow, color selective, high acuityc) slow, color selective, high acuity

M cells --> Magnocellular pathwayM cells --> Magnocellular pathway P cells --> Parvocellular pathwayP cells --> Parvocellular pathway Their output remains segregated in V1 & beyondTheir output remains segregated in V1 & beyond

Cytochrome oxidase stain reveals subregions in V1

A Schematic of What vs. Where A Schematic of What vs. Where

What vs. Where in HumansWhat vs. Where in Humans

Focal lesions produce selective color or Focal lesions produce selective color or motion blindness.motion blindness. cortical color blindness (achromatopsia)cortical color blindness (achromatopsia) motion blindness (akinetopsia)motion blindness (akinetopsia)

Positron Emission Tomography (PET) studies in Positron Emission Tomography (PET) studies in Humans reveal:Humans reveal: Motion Area distinct from color areaMotion Area distinct from color area (e.g. Zeki and colleagues, 1990.)(e.g. Zeki and colleagues, 1990.)

Artwork pre and post achromatopsiaArtwork pre and post achromatopsia

AchromatopsiaAchromatopsia

Inability to perceive color-- color knowledge Inability to perceive color-- color knowledge and color naming can be intact.and color naming can be intact.

acquiredacquired after cortical brain damage after cortical brain damage distinct from congenital color blindness distinct from congenital color blindness

(photoreceptor abnormality)(photoreceptor abnormality) Subjective reports...Subjective reports... Lesion locus: bilateral occipito-temporal Lesion locus: bilateral occipito-temporal

lesions associated w/upper visual field lesions associated w/upper visual field deficits.deficits.

AkinetopsiaAkinetopsia

Acquired inability to motionAcquired inability to motion Subjective reports...Subjective reports... Lesion locus: bilateral occipito-parietal Lesion locus: bilateral occipito-parietal

involving area MT/V5.involving area MT/V5.

PET Activation Study LogicPET Activation Study Logic

• Perceptual/cognitive Perceptual/cognitive activity mediated by activity mediated by localized neural localized neural activity.activity.

• Blood flow changes Blood flow changes accompany regional accompany regional changes in neural changes in neural activity. activity.

• Blood flow changes Blood flow changes measured by measured by monitoring monitoring distribution of distribution of radioactive tracer.radioactive tracer.

Regions active in response to COLOR

Regions active in response to MOTION