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When: 2/23 8-10 PMWhen: 2/23 8-10 PM

Where: 182 Where: 182 DennisonDennison

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Examining the Examining the what pathwaywhat pathway

The Visual AgnosiasThe Visual Agnosias Neurocognitive Neurocognitive

architecture of visual architecture of visual recognitionrecognition

This LectureThis LectureThis LectureThis Lecture

Two-processor model of visual recognition Two-processor model of visual recognition What vs. What vs. HowHow The Where PathwayThe Where Pathway

Balint’s syndromeBalint’s syndrome Unilateral NeglectUnilateral Neglect

Farah theory: Two specialized (lateralized?) processors

I. PART DECOMPOSITION:I. PART DECOMPOSITION: used heavily for word identification but also objectsused heavily for word identification but also objects LH dominantLH dominant

II. WHOLISTIC PROCESSING:II. WHOLISTIC PROCESSING: Used for complex objects without part Used for complex objects without part

decomposition--> facesdecomposition--> faces RH dominantRH dominant

Object recognition relies on both Object recognition relies on both to varying degrees--> to varying degrees--> one may compensate for the other.one may compensate for the other.

Evidence for two processorsEvidence for two processors

Object agnosia co-occurs with pure alexia.Object agnosia co-occurs with pure alexia. Object agnosia co-occurs with prosopagnosiaObject agnosia co-occurs with prosopagnosia Rarely, if ever, does object agnosia occur Rarely, if ever, does object agnosia occur

without either pure alexia or prosopagnosia.without either pure alexia or prosopagnosia.

Wholistic processing

Part Decomposition

Case D.F. Case D.F. (Milner & Goodale, 1995)(Milner & Goodale, 1995)

Classic Apperceptive Classic Apperceptive AgnosicAgnosic

Severly impaired FORM Severly impaired FORM perceptionperception

Damage to V2, V3, V4-- Damage to V2, V3, V4-- Ventral StreamVentral Stream

Intact abilities should Intact abilities should reflect operation of dorsal reflect operation of dorsal streamstream

Dissociating Dissociating WhatWhat

from from HowHow

Orientation reports: Orientation reports: IMPAIREDIMPAIRED verbalverbal matchingmatching

Posting behavior Posting behavior SPAREDSPARED

Implication:Implication: Orientation & Orientation & shape representations shape representations available for guiding available for guiding actionaction

D.F. Control

Perceptualmatching

Visuomotorposting

Damaging the Damaging the WhereWhere Pathway...Pathway...

Balint's SyndromeBalint's Syndrome (1909) A disorder of space (1909) A disorder of space exploration and space cognition...exploration and space cognition...

A cluster co-occuring visuomotor & A cluster co-occuring visuomotor & visuospatial disturbancesvisuospatial disturbances

Results from Bilateral Posterior Parietal Results from Bilateral Posterior Parietal damagedamage

A note about A note about SyndromesSyndromes

Collection of deficits or symptoms that co-Collection of deficits or symptoms that co-occur occur Are all symptoms due to Are all symptoms due to oneone underlying underlying

impairment? (common mechanism?)impairment? (common mechanism?)

OROR Do they co-occur because underlying Do they co-occur because underlying

mechanisms are located in adjacent brain mechanisms are located in adjacent brain structures? (co-localization?)structures? (co-localization?)

If latter, then dissociations should eventually If latter, then dissociations should eventually be found.be found.

Normal scanpaths

Gaze apraxic scanpaths

Back and forth between two points

Outlining the Perimeter of a rectangle

Elements of Balint'sElements of Balint's

gaze apraxia:gaze apraxia: inability to move the eyes voluntarily inability to move the eyes voluntarily to points in the visual field.to points in the visual field. spontaneous, reflexive movements sparedspontaneous, reflexive movements spared

optic ataxiaoptic ataxia (disorder of reaching): impairment in (disorder of reaching): impairment in visually guided movements of the limbs.visually guided movements of the limbs. some improvement with eyes closed.some improvement with eyes closed.

Normal Optic Ataxia Optic Ataxia

Posting performance Balint’sPosting performance Balint’s

Elements of Balint'sElements of Balint's

gaze apraxia:gaze apraxia: inability to move the eyes voluntarily inability to move the eyes voluntarily to points in the visual field.to points in the visual field. spontaneous, reflexive movements sparedspontaneous, reflexive movements spared

optic ataxiaoptic ataxia (disorder of reaching): impairment in (disorder of reaching): impairment in visually guided movements of the limbs.visually guided movements of the limbs. some improvement with eyes closed.some improvement with eyes closed.

spatial disorientation:spatial disorientation: inability to appreciate the inability to appreciate the "spatial properties" of objects."spatial properties" of objects.

distance and size estimates impaired.distance and size estimates impaired. impaired whole body movement in space.impaired whole body movement in space.

Place a point in the centerPlace a point in the center

Divide the circle in twoDivide the circle in two

Draw the outline of a faceDraw the outline of a face

Draw the facial featuresDraw the facial features

Elements of Balint'sElements of Balint's

gaze apraxia:gaze apraxia: inability to move the eyes voluntarily to inability to move the eyes voluntarily to points in the visual field.points in the visual field. spontaneous, reflexive movements sparedspontaneous, reflexive movements spared

optic ataxiaoptic ataxia (disorder of reaching): impairment in visually (disorder of reaching): impairment in visually guided movements of the limbs.guided movements of the limbs. some improvement with eyes closed.some improvement with eyes closed.

spatial disorientation: inability to appreciate the "spatial spatial disorientation: inability to appreciate the "spatial properties" of objects.properties" of objects.

distance and size estimates impaired.distance and size estimates impaired. impaired whole body movement in space.impaired whole body movement in space.

simultanagnosia:simultanagnosia: the inability to see more than one object the inability to see more than one object at a time.at a time.

““It is difficult: I don’t see at the same time bothIt is difficult: I don’t see at the same time both--- the pencil and the circle. The hand does not --- the pencil and the circle. The hand does not movewhen I want it to move.” movewhen I want it to move.” (from Luria et al., 1954)(from Luria et al., 1954)

Drawing a circleDrawing a circle

Tracing a circleTracing a circle

The drawing of a circle in between two already drawnThe drawing of a circle in between two already drawn

Lesion site in Balint’s

Implications Implications

Parietal lobes are important forParietal lobes are important for representations that guide spatial behaviorsrepresentations that guide spatial behaviors the the howhow and where pathway and where pathway allocating attention (shifting overtly and covertly)allocating attention (shifting overtly and covertly)

Covert Attention as a SpotlightCovert Attention as a Spotlight

Attention selects Attention selects information.information.

Fate of unattended Fate of unattended input?input?

Filter theory of AttentionFilter theory of Attention

Locus of selection?Locus of selection?

Brain Regions Activated During Attention ShiftingBrain Regions Activated During Attention Shifting

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What is wrong with this patient?What is wrong with this patient?

Symptoms observed:Symptoms observed: left hemiparetic armleft hemiparetic arm anosagnosia- unawareness / denial of illness.anosagnosia- unawareness / denial of illness. rightward gaze deviationrightward gaze deviation no obvious hemianopiano obvious hemianopia Visual extinction to double simultaneous stimulationVisual extinction to double simultaneous stimulation Tactile extinction to DSSTactile extinction to DSS Constructional apraxia: deficit in constructional and Constructional apraxia: deficit in constructional and

drawing tasksdrawing tasks apraxia: disorder of skilled movementapraxia: disorder of skilled movement

allesthesia: (gross) mislocalization of stimulationallesthesia: (gross) mislocalization of stimulation

Unilateral (LEFT) neglect: Unilateral (LEFT) neglect:

A deficit in perceiving & responding to A deficit in perceiving & responding to stimulation on the side opposite to the stimulation on the side opposite to the damaged hemisphere.damaged hemisphere.

Typical lesion site: unilateral parietal-occipital Typical lesion site: unilateral parietal-occipital junction (Brodmann's area 7, 40)junction (Brodmann's area 7, 40) QuickTime™ and a

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Examples of Neglect PerformanceExamples of Neglect Performance