Announcement MIDTERM When: 2/ PM Where: 128 Dennison

Last Lecture What/Where pathways in humans Attribute specific deficits Attribute specific deficits Neuroimaging evidence Neuroimaging evidence

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

The What Pathway: How object recognition breaks down THE VISUAL AGNOSIAS Deficits in object and form recognition: modality-specific deficit in recognition modality-specific deficit in recognition not due to naming impairment not due to naming impairment not due to memory impairment not due to memory impairment not due to deficits in elementary sensation not due to deficits in elementary sensation Classic Distinction: Apperceptive versus Associative Agnosia: affect different "stages" of visual processing Apperceptive versus Associative Agnosia: affect different "stages" of visual processing

Apperceptive Agnosia  impaired shape identification  impaired copying  impaired matching  difficulty judging orientation: (horizontal vs. vertical)  can trace an image / misled by stray lines  field defects sometimes  some cases "helped" by object motion  can reach for objects accurately; negotiate a path  Domain general: words, objects, faces are all affected.

Apperceptive Agnosia Impaired CopyImpaired Matching

Associative Agnosia Impaired recognition of complex forms and objects. Impaired recognition of complex forms and objects. In contrast to Apperceptives, early visual processing is much more INTACT. In contrast to Apperceptives, early visual processing is much more INTACT. Simple form recognition is intact Simple form recognition is intact Copying and Matching OK Copying and Matching OK Traditional View: Visual perception stripped of meaning Perception is intact Perception is intact impairment associating percept with stored knowledge impairment associating percept with stored knowledge

Associative Agnosics can copy...

More examples of spared copying...

Associative Agnosia Stored Knowledge is (largely) intact Stored Knowledge is (largely) intact Evidence: verbal descriptions and drawings from memory Evidence: verbal descriptions and drawings from memory Helped by context: better with real objects in scenes than isolated drawings. Helped by context: better with real objects in scenes than isolated drawings. Lesion Locus: typically bilateral ventral (occipital-temporal pathway). Lesion Locus: typically bilateral ventral (occipital-temporal pathway).

Integrative Visual Agnosia Can copy, but in a labored, fragmented manner. Can copy, but in a labored, fragmented manner. Has difficulty integrating parts into a whole. Has difficulty integrating parts into a whole. Deficit is intermediate (between apperceptive & associative). Deficit is intermediate (between apperceptive & associative).

Semanticknowledge image Shape coding Figure/ground Feature integration Grouping Mapping to Structural * description Stages of visual recognition Structural description: representations of shape that are composed of parts and the spatial relations among the parts.

CLOSURE SIMILARITY GOOD CONTINUATION PROXIMITY GESTALTGROUPINGPRINCIPLES

Semanticknowledge image Shape coding Figure/ground Feature integration Grouping Mapping to Structural * description Stages of visual recognition Structural description: representations of shape that are composed of parts and the spatial relations among the parts.

Semanticknowledge image Shape coding Figure/ground Feature integration grouping Mapping to Structural description APPERCEPTIVE AGNOSIA Locus of recognition deficit?

Semanticknowledge image Shape coding Figure/ground Feature integration grouping Mapping to Structural description INTEGRATIVE AGNOSIA Locus of recognition deficit?

Semanticknowledge image Shape coding Figure/ground Feature integration grouping Mapping to Structural description ASSOCIATIVE AGNOSIA Locus of recognition deficit?

Visual Agnosia Summary "Percepts" undergo many transformations so recognition deficits are variable. "Percepts" undergo many transformations so recognition deficits are variable. Apperceptive agnosia - early deficit, affecting all visual materials (objects, faces, words). Apperceptive agnosia - early deficit, affecting all visual materials (objects, faces, words). impaired copy and matching impaired copy and matching Deficit in shape coding stage Deficit in shape coding stage Integrative Agnosia Integrative Agnosia can be material-specific (word or face processing may be spared) can be material-specific (word or face processing may be spared) copying is slavish and labored copying is slavish and labored deficit in figure/ground segregation, grouping deficit in figure/ground segregation, grouping

… Summary continued Associative agnosia - a "later" deficit of perception & association. Associative agnosia - a "later" deficit of perception & association. can be material-specific (e.g., word or face processing may be spared) can be material-specific (e.g., word or face processing may be spared) Does this agnosia category really exist or are they all integrative agnosics? Does this agnosia category really exist or are they all integrative agnosics? Material-specificity of visual agnosias suggests specialized visual processors. Material-specificity of visual agnosias suggests specialized visual processors.

Prosopagnosia: Evidence for a special purpose face processor? Impairment in recognizing familiar faces Impairment in recognizing familiar faces Person recognition can occur non-visually Person recognition can occur non-visually Person memory is intact Person memory is intact Reading and object recognition may be "intact" Reading and object recognition may be "intact" Bilateral Ventral path lesions (or RH only?) Bilateral Ventral path lesions (or RH only?)

How selective is the impairment? Aspects of face processing may be spared Face matching Face matching Age and gender ID Age and gender ID Facial Emotion ID Facial Emotion ID Non-face stimuli may be affected Impaired within class animal recognition Impaired within class animal recognition former bird watcher: "all the birds look the same" former bird watcher: "all the birds look the same" farmer: unable to distinguish among his cows (zooagnosia???) farmer: unable to distinguish among his cows (zooagnosia???) Some pure cases exist: DeRenzi (1986) Some pure cases exist: DeRenzi (1986)

How do we process faces? Yin’s (1970) Inversion effect Face recognition suffers more from inversion than other objects. Face recognition suffers more from inversion than other objects. Specialized configurational processor Specialized configurational processor

Semanticknowledge image Shape coding Figure/ground Feature integration grouping Mapping to Structural description Figure/ground Feature integration grouping Mapping to Structural description Semanticknowledge

Semanticknowledge image Shape coding Figure/ground Feature integration grouping Mapping to Structural description Figure/ground Feature integration grouping Mapping to Structural description Semanticknowledge

Special purpose letter processor? (Pure) Alexia Pure Alexia : acquired reading impairment without other salient language deficits. Pure Alexia : acquired reading impairment without other salient language deficits. patients read letter-by-letter patients read letter-by-letter word knowledge is intact word knowledge is intact Can dissociate from other recognition problems Can dissociate from other recognition problems Co-occurs with achromatopsia Co-occurs with achromatopsia Upper RVF quadrantanopia Upper RVF quadrantanopia Unilateral LH lesion occipital-temporal region (area 19 / 37) Unilateral LH lesion occipital-temporal region (area 19 / 37)

Face recognition requires encoding of relations among parts (gestalt) without decomposing into parts. requires encoding of relations among parts (gestalt) without decomposing into parts. identification does not depend on any particular part (e.g. the nose) identification does not depend on any particular part (e.g. the nose) Not so for Words: Parts must be specified. Parts must be specified. Distinguishing WORD from WORK Distinguishing WORD from WORK Face and Word Deficits Doubly Dissociate

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: for complex objects without part decomposition--> faces 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, do pure alexia and prosopagnosia occur without object agnosia. Rarely, if ever, do pure alexia and prosopagnosia occur without object agnosia. Holistic processing Part Decomposition

Semanticknowledge image Shape coding Figure/ground Feature integration grouping Mapping to Structural description Figure/ground Feature integration grouping Mapping to Structural description Semanticknowledge A M g e h K