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
Visual Field Defects have localizing significance
Blumenfeld, 2002
Separate “Channels” for Motion, Form and Color
Blumenfeld, 2002
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”
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
Spiridon, Fischl, & Kanwisher, Hum Brain Mapping, 2006
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
Associative Agnosia
• inability to recognize or
name objects
• subject cannot copy
unrecognized objects
• strong evidence for
sensory-perceptual
disturbance
• 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
V-AP
A-AP
Frontal
AS
Temporal
Occipital
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
Anatomy of Visual-Verbal Disconnection
Language
Area
(naming)
L Occipital Lobe
Corpus
Callosum
R Occipital Lobe
Cognitive Models of Object
Recognition
• Provide “box-models” of stages of
information processing
• Proposed stages derived from cognitive
performance data in normals and brainimpaired 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.
proximity
similarity
good continuation
closure
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
Face-Name Learning
vs.
Demi Moore
Winona Ryder
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
2500
2000
Fam-Rel
Fam-Neu
Fam-Un
Unfam
1500
1000
500
0
Face
Name
Overall
P.H.