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Announcement

Announcement. MIDTERM When: 2/23 8-10 PM Where: 128 Dennison. Last Lecture. What/Where pathways in humans Attribute specific deficits Neuroimaging evidence. This Lecture. Examining the what pathway The Visual Agnosias Neurocognitive architecture of visual recognition.

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Announcement

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  1. Announcement MIDTERM When: 2/23 8-10 PM Where: 128 Dennison

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

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

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

  5. 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.

  6. Apperceptive Agnosia Impaired Copy Impaired Matching

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

  8. Associative Agnosics can copy...

  9. More examples of spared copying...

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

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

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

  13. GOOD CONTINUATION CLOSURE GESTALT GROUPING PRINCIPLES SIMILARITY PROXIMITY

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

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

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

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

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

  19. … Summary continued • Associative agnosia - a "later" deficit of perception & association. • 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? • Material-specificity of visual agnosias suggests specialized visual processors.

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

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

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

  23. Semantic knowledge Mapping to Structural description Mapping to Structural description Figure/ground Feature integration grouping Shape coding image Figure/ground Feature integration grouping Semantic knowledge OBJECTS FACES

  24. Semantic knowledge Mapping to Structural description Mapping to Structural description Figure/ground Feature integration grouping Shape coding image Figure/ground Feature integration grouping Semantic knowledge OBJECTS ...LETTERS... FACES

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

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

  27. Farah theory: Two specialized (lateralized?) processors I. PART DECOMPOSITION: • used heavily for word identification but also objects • LH dominant II. WHOLISTIC PROCESSING: • for complex objects without part decomposition--> faces • RH dominant • Object recognition relies on both • to varying degrees--> • one may compensate for the other.

  28. Part Decomposition Holistic processing Evidence for two processors • Object agnosia co-occurs with pure alexia. • Object agnosia co-occurs with prosopagnosia • Rarely, if ever, do pure alexia and prosopagnosia occur without object agnosia. Words

  29. h Mapping to Structural description Mapping to Structural description Shape coding image Part Decomposition M e g A K Semantic knowledge Figure/ground Feature integration grouping Figure/ground Feature integration grouping Semantic knowledge holistic processor

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