Agnosia and Perceptual Disturbances March 17, 2008

1. Agnosia and Perceptual Disturbances March 17, 2008

2. Key Concepts • Visual system is modular, organized by subdomain • Patterns of impairment reveal organization • Agnosia results from modality-specific knowledge access defects • Understanding underlying cognitive substrate aids identification and evaluation • No real data on rehabilitation

3. Clinical Scenario • Patient presents with visual complaints • may complain that the visual world is subjectively different or that objects/faces “all look the same” • typically will have some visual field defect (though this is not required) • Patient is unable to name, demonstrate the use of, or otherwise recognize the nature of objects (may be general, specific, or hyperspecific) • Patient is not demented nor does the patient have extensive language disturbance

4. Visual Field Defects have localizing significance Blumenfeld, 2002

6. Separate “Channels” for Motion, Form and Color Blumenfeld, 2002

8. Multiple Visual Areas in the Monkey

9. Object vs. Spatial Vision General principle: inferior lesionsproduceperceptual impairments;superior lesionsproduce syndromesdominated byspatial impairment

10. V4 (color) FFA (face)

11. Two Models: -domain-specificity/neural substrate (modules) -process-specificity

12. Neural Substrate Example: the “Fusiform Face Area”

13. Multiple modules? -Occipital Face Area (OFA) -Fusiform Face Area (FFA) -Parahippocampal Place Area (PPA) -Extrastriate Body Area (EBA) -MT (biological movement) Spiridon, Fischl, & Kanwisher, Hum Brain Mapping, 2006

14. Processing within modules is not completely domain specific Spiridon, Fischl, & Kanwisher, Hum Brain Mapping, 2006

15. Agnosia • Failure to recognize previously familiar stimuli • Modality-specific • Not due to dementia, aphasia, or unfamiliarity with stimulus • May (or may not) be limited to particular classes of stimuli

16. Agnosia Examples • Prosopagnosia (impairment in recognizing familiar faces) • Auditory Sound Agnosia (impairment in recognizing sounds of common objects) • Phonagnosia (impairment in recognizing familiar people by their voices) • Tactile agnosia (impairment in recognizing what’s placed in the hand)

17. Apperceptive Agnosia inability to recognize or name objects subject cannot copy unrecognized objects strong evidence for sensory-perceptual disturbance Associative Agnosia inability to recognize or name objects subject can generally copy unrecognized objects sensory-perceptual disturbance cannot explain recognition defect Classes of Agnosia(Lissauer’s stage model, 1880’s)

18. Apperceptive Agnosia (Benson & Greenberg, 1969)

19. Associative Agnosia (Farah, Hammond, Levine, et al., 1988)

20. Anatomy implied in Stage Model V-AP A-AP Occipital Frontal AS Temporal

21. Other Ways of Classifying Agnosia • Stage/level (apperceptive, associative) • Function (shape/form, integrative) • Modality (visual, auditory, tactile) • Domain (objects, faces, colors, sounds) • Category (living things, moving things)

22. To “Recognize” Something, you have to…. • Detect it • Perceive it in an organized way • Discriminate it from other like objects • Related it to something you’ve perceived before • Understand it as familiar or unfamiliar • Unlock information about its meaning • Access the name or verbal referent

23. Explanations of Agnosia • Failure of perception to contact language (visual-verbal disconnection) • Failure of perception to contact memory • Impairment/degradation of a stored representation of an object in memory • Sensory-perceptual impairment

24. Anatomy of Visual-Verbal Disconnection Corpus Callosum Language Area (naming) R Occipital Lobe L Occipital Lobe

25. Cognitive Models of Object Recognition • Provide “box-models” of stages of information processing • Proposed stages derived from cognitive performance data in normals and brain-impaired patients • Help to decompose complex abilities into their constituent components

27. Steps in Assessment of Agnosia • Determine whether, in fact, the deficit is “agnosic” • Test for “boundary” conditions (aphasia, amnesia, dementia; modality specificity) • Qualify the nature of the deficit • Determine conditions under which recognition succeeds and fails • Determine the functional locus of the deficit • In perception, familiarity detection, semantic/memory access, etc.

29. proximity similarity good continuation closure

31. Defects in the “Initial Representation” • Visual Form Agnosia: failure in the appreciation of form or shape • Simultaneous Agnosia: inability to appreciate meaning of more than one stimulus • Dorsal: bilateral occipitoparietal disease • Ventral: left occipitoparietal junction

32. Apperceptive Agnosia (Benson & Greenberg, 1969)

37. Minimal Feature Match Foreshortened Match

38. Associative Agnosia (Farah, Hammond, Levine, et al., 1988)

40. BORB Object Decision Task

41. Face-Name Learning vs. Demi Moore Winona Ryder

43. BORB Association Match

44. Clinical Features of Prosopagnosia • Inability to identify previously familiar people by facial features alone • Intact ability to identify people using nonfacial features (voice) • May extend to nonfacial stimuli • May co-exist with object agnosia • May take apperceptive and associative forms

45. Frequent Co-existing Signs • Object agnosia • Visual recent memory loss, and other signs of visual-limbic disconnection • Superior visual field defects • Altitudinal hemianopia • Superior quadrantanopia • Achromatopsia • Topographical agnosia

46. Lesion Profile in Prosopagnosia • Bilateral occipitotemporal • Extent of damage determines presence of apperceptive defect • Unilateral (right) occipitotemporal • Examples from recent cases

49. Prosopagnosics can: Discriminate age Discriminate gender Recognize emotions Recognize faces as such Match faces Show ‘indirect’ knowledge about faces Prosopagnosics can’t: Identify individuals Describe the owner of the face (semantics) Feel familiarity when viewing faces (Variable) identify individuals in other categories Spared and Impaired Abilities in Prosopagnosia