Agnosia and Perceptual Disturbances March 17, 2008

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

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

Blumenfeld, 2002 Visual Field Defects have localizing significance

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

Multiple Visual Areas in the Monkey

Object vs. Spatial Vision General principle: inferior lesions produce perceptual impairments; superior lesions produce syndromes dominated by spatial impairment

V4 (color) FFA (face)

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

Neural Substrate Example: the “Fusiform Face Area”

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

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

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)

Classes of Agnosia (Lissauer’s stage model, 1880’s) 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

Apperceptive Agnosia (Benson & Greenberg, 1969)

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

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

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)

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

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

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

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

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.

proximitysimilarity good continuationclosure

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

Apperceptive Agnosia (Benson & Greenberg, 1969)

Minimal Feature Match Foreshortened Match

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

BORB Object Decision Task

Demi MooreWinona Ryder vs. Face-Name Learning

BORB Association Match

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

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

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

Spared and Impaired Abilities in Prosopagnosia 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

Bill Clinton Vladimir Putin Daniel Day-Lewis DeHaan, Bauer, & Greve, 1992

Meryl Streep

Vladimir Putin

John Edwards

Sebastian Weisdorf

Richard Nixon

John F. Kennedy

Cross-Domain Semantic Priming