Announcement MIDTERM When: 2/ PM Where: 182 Dennison

Last Lecture Examining the what pathway The Visual Agnosias The Visual Agnosias Neurocognitive architecture of visual recognition Neurocognitive architecture of visual recognition

This Lecture Two-processor model of visual recognition Two-processor model of visual recognition What vs. How What vs. How The Where Pathway The Where Pathway Balint’s syndrome Balint’s syndrome Unilateral Neglect Unilateral Neglect

Farah theory: Two specialized (lateralized?) processors I. PART DECOMPOSITION: used heavily for word identification but also objects used heavily for word identification but also objects LH dominant LH dominant II. WHOLISTIC PROCESSING: Used for complex objects without part decomposition--> faces Used for complex objects without part decomposition--> faces RH dominant RH 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 processors Object agnosia co-occurs with pure alexia. Object agnosia co-occurs with pure alexia. Object agnosia co-occurs with prosopagnosia Object agnosia co-occurs with prosopagnosia Rarely, if ever, does object agnosia occur without either pure alexia or prosopagnosia. Rarely, if ever, does object agnosia occur without either pure alexia or prosopagnosia. Wholistic processing Part Decomposition

Case D.F. (Milner & Goodale, 1995) Classic Apperceptive Agnosic Classic Apperceptive Agnosic Severly impaired FORM perception Severly impaired FORM perception Damage to V2, V3, V4-- Ventral Stream Damage to V2, V3, V4-- Ventral Stream Intact abilities should reflect operation of dorsal stream Intact abilities should reflect operation of dorsal stream

Dissociating What from How Orientation reports: IMPAIRED Orientation reports: IMPAIRED verbal verbal matching matching Posting behavior SPARED Posting behavior SPARED Implication: Orientation & shape representations available for guiding action D.F. Control Perceptual matching Visuomotor posting

Damaging the Where Pathway... Balint's Syndrome (1909) A disorder of space exploration and space cognition... A cluster co-occuring visuomotor & visuospatial disturbances A cluster co-occuring visuomotor & visuospatial disturbances Results from Bilateral Posterior Parietal damage Results from Bilateral Posterior Parietal damage

A note about Syndromes Collection of deficits or symptoms that co- occur Are all symptoms due to one underlying impairment? (common mechanism?) Are all symptoms due to one underlying impairment? (common mechanism?)OR Do they co-occur because underlying mechanisms are located in adjacent brain structures? (co-localization?) Do they co-occur because underlying mechanisms are located in adjacent brain structures? (co-localization?) If latter, then dissociations should eventually be found.

Normal scanpaths Gaze apraxic scanpaths

Back and forth between two points Outlining the Perimeter of a rectangle

Elements of Balint's gaze apraxia: inability to move the eyes voluntarily to points in the visual field. gaze apraxia: inability to move the eyes voluntarily to points in the visual field. spontaneous, reflexive movements spared spontaneous, reflexive movements spared optic ataxia (disorder of reaching): impairment in visually guided movements of the limbs. optic ataxia (disorder of reaching): impairment in visually guided movements of the limbs. some improvement with eyes closed. some improvement with eyes closed.

Normal Optic Ataxia Optic Ataxia Posting performance Balint’s

Elements of Balint's gaze apraxia: inability to move the eyes voluntarily to points in the visual field. gaze apraxia: inability to move the eyes voluntarily to points in the visual field. spontaneous, reflexive movements spared spontaneous, reflexive movements spared optic ataxia (disorder of reaching): impairment in visually guided movements of the limbs. optic ataxia (disorder of reaching): impairment in visually guided movements of the limbs. some improvement with eyes closed. some improvement with eyes closed. spatial disorientation: inability to appreciate the "spatial properties" of objects. spatial disorientation: inability to appreciate the "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 center Divide the circle in two

Draw the outline of a face Draw the facial features

Elements of Balint's gaze apraxia: inability to move the eyes voluntarily to points in the visual field. gaze apraxia: inability to move the eyes voluntarily to points in the visual field. spontaneous, reflexive movements spared spontaneous, reflexive movements spared optic ataxia (disorder of reaching): impairment in visually guided movements of the limbs. optic ataxia (disorder of reaching): impairment in visually guided movements of the limbs. some improvement with eyes closed. some improvement with eyes closed. spatial disorientation: inability to appreciate the "spatial properties" of objects. spatial disorientation: inability to appreciate the "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. simultanagnosia: the inability to see more than one object at a time. simultanagnosia: the inability to see more than one object at a time.

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

The drawing of a circle in between two already drawn

Lesion site in Balint’s

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

Covert Attention as a Spotlight Attention selects information. Attention selects information. Fate of unattended input? Fate of unattended input?

Filter theory of Attention

Locus of selection?

Brain Regions Activated During Attention Shifting

What is wrong with this patient? Symptoms observed: left hemiparetic arm left hemiparetic arm anosagnosia- unawareness / denial of illness. anosagnosia- unawareness / denial of illness. rightward gaze deviation rightward gaze deviation no obvious hemianopia no obvious hemianopia Visual extinction to double simultaneous stimulation Visual extinction to double simultaneous stimulation Tactile extinction to DSS Tactile extinction to DSS Constructional apraxia: deficit in constructional and drawing tasks Constructional apraxia: deficit in constructional and drawing tasks apraxia: disorder of skilled movement apraxia: disorder of skilled movement allesthesia: (gross) mislocalization of stimulation allesthesia: (gross) mislocalization of stimulation

Unilateral (LEFT) neglect: A deficit in perceiving & responding to stimulation on the side opposite to the damaged hemisphere. A deficit in perceiving & responding to stimulation on the side opposite to the damaged hemisphere. Typical lesion site: unilateral parietal-occipital junction (Brodmann's area 7, 40) Typical lesion site: unilateral parietal-occipital junction (Brodmann's area 7, 40)

Examples of Neglect Performance