raffaella ida rumiati - sissa - international school for advanced
TRANSCRIPT
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Agnosias & Semantic Deficits
Raffaella Ida Rumiati
Cognitive Neuroscience Sector
SISSA
Trieste, Italy
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INTRODUCTION
• The study of several neuropsychological disorders such as agnosia, optic aphasia, semantic dementia, and category selective deficits has provided us with a valuable insight as to the cerebral organization of meaning
• Moreover, disorders of object perception have offered cues as to the human visual recognition abilities
• In this lecture, I am going to review a number of studies that have challenged our contemporary view on these issues
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AGNOSIA
• This is a reduced ability to identify stimuli presented in a given sensory modality as a consequence of brain damage
• Depending on which modality is affected, we talk about visual, auditory or tactile agnosia
VISUAL AGNOSIA • This is the most studied type: easier to detect
• Stimuli misrecognized visually, can be recognized:
– through tactile manipulation
– from verbal description
– based on its characteristic sound or noise
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Il caso di Heinrich Lissauer (1890) • He described the case of an 80-year-old patient, GL, who had
been blown against a wooden fence by a storm, knocking his head
• After this accident, he could still see but he could not identify common objects visually presented
• GL had almost normal visual acuity for his age, and he could draw accurate copies of seen objects he could not recognize
• His knowledge of objects was preserved: he would refer to them appropriately in conversation, recognize them when he could touch them or listen to their characteristic sound
• Thus GL suffered from visual associative agnosia
• The post-mortem analysis revealed a lesion in the left temporo-occipital junction
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The patient could copy the items he could not recognize
(Rubens & Benson 1971)
COPYING LINE DRAWINGS
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• He proposed a model of visual recognition that distinguishes two levels:
– apperceptive: that accomplishes early perceptual
processing of the stimuli
– associative: that provides a meaning to the percept by
linking it to previous experience
• Depending on which of the two levels is impaired as a result of brain damage, we will observe apperceptive or associative agnosia respectively
Lissauer‟s Model
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After Lissauer
• Some skeptics (Bay 1952; Bender & Feldman 1972; Farah 1990) have argued that:
– visual agnosia does not exist
– so-called agnosic patients have either an elementary sensory deficit or an intellectual decline
• The original dichotomy proposed by Lissauer was maintained but each level has been further fractionated
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Lissauer
• Apperceptive
• Associative
Warrington & co.
• Pseudoagnosia: sensory discrimination, shape detection and discrimination
• Apperceptive: figure-ground, incomplete drawings, perceptual categorization
• Associative
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WARRINGTON & COLLEAGUES
Pseudoagnosia: Shape discrimination
Efron test
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Pseudoagnosia: Shape detection
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Apperceptive Agnosia
Figure-Ground
Ghent overlapping figure test
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Apperceptive Agnosia
Incomplete drawings
Gollin‟s test
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Perceptual
Categorization:
– Patients with RBD
(parietal lesions)
• spared shape
recognition
• impaired identification
and matching of objects
depicted in unusual
views
• deficit particularly
severe when main axis
is shortened or a critical
feature is occluded.
Matching unusual views
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Lissauer
• Apperceptive
• Associative
Humphreys & Co.
• Appreceptive:
• Integrative agnosia:
– inability to group and integrate parts of an object into a
coherent whole
• SDS
• Semantic
System
Warrington & Co.
• Pseudoagnosia
• Apperceptive: figure-ground, completion, perceptual categorization
• Associative
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Integrative Agnosia
– Deficit in integrating single features of a stimulus in a coherent fashion
– Failure to extract a figure from the background
– Accurate copy of drawings and objects
– Good identification of elementary shapes
– Good semantic memory (e.g. drawing from memory)
HJA, Humphreys & Riddoch, 1987
HG, Grailet et al., 1990
Humphreys & Co.
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• THE STRUCTURAL DESCRIPTION SYSTEM
– contains representations which define geometrical
and volumetric properties of objects
– is for objects what the input phonological lexicon is
for words
• THE SEMANTIC SYSTEM
– stores functional knowledge about objects,
associations between them, the context in which
they can be found as well as the encyclopedic
knowledge about them
DIFFERENT TYPES OF ASSOCIATIVE A.
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Object decision (chimeras)
• In analogy with the lexical decision task that assesses the integrity of the phonological input lexicon, the object decision task assesses the integrity of the SDS:
– patients are asked to decide whether a given stimulus exists in their repertoire of visual descriptions.
Head Test
• Matching a given “body” of an animal or object to the correct “head” is also supposed to tap the SDS
Other Tests
• Drawing an object from memory, describing its shape, or evoking its perceptual features may not detect the SDS but it could reflect a possible imagery deficit
How to assess the SDS
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– Naming from different modalities (semantic errors)
– Sorting items into categories (living vs non living)
– Semantic matching tasks
• Which 2 items are used together (hammer & nail)
• Which 2 items are found in the same context (P & P)
• Which 2 items share the same function (radio & CD player)
– Questions concerning visual perceptual and functional
associative knowledge (Barbarotto et al. 1996; Silveri &
Gainotti 1988)
– Pantomiming the use of objects
*All these tests can also be administered using verbal stimuli
Testing the Semantic System
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Picture-to-Picture Matching
Pyramid & Palm Tree Test
Word-to-Word Matching
Pyramid & Palm Tree Test
pine tree life preserver
tulip palm tree
pyramid
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Barbarotto et al. 1996
Questionnaire
HAMMER 1. supraordinate info: is it an object, a vegetable or an
animal?
2. category info: is it a tool, a musical instrument or a gem?
3. subordinate perceptual info: is it made of glass, of metal or of cement?
4. subordinate structural info: is it smaller than a screw? (yes/no)
5. functional info: is it used for cutting, screwing or sticking nails?
6. the protypical user of the object: is it used by the painter, the carpenter, the glazer?
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• Based on double dissociations, it has been proposed that stored knowledge is organized in two separate subsystems:
1. Patients with a damaged SDS but spared semantic system proper
2. Patients who performed normally on the object decision task but pathologically on tasks tapping semantic knowledge
Pattern 1: Sartori & Job 1988; Caramazza & Shelton 1998 (for animals only)
Pattern 2: Riddoch & Humphreys 1987; Stewart Parkin & Hunkin 1992; Sheridan & Humphreys 1993; Hillis & Caramazza 1995; Humphreys & Riddoch 1999; Fery & Morais 2003
SDS & Semantic System
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• Agnosic deficits have been explained
in different ways, depending on which
model of semantic organization was
adopted
• Two main views:
• Multiple-semantic systems
• Amodal semantic system (also called Organized-Unitary-Content hypothesis,
OUCH by Caramazza et al.)
ASSOCIATIVE A. & SEMANTIC SYSTEM
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• This view holds that the conceptual knowledge is organized in modality specific systems (e.g. verbal, visual):
– different modalities will be tapped by different stimuli (e.g. words, pictures)
• Evidence for separate systems comes from patients who showed a selective deficit in either processing words or processing pictures
Shallice1988; McCarthy & Warrington 1994
MULTIPLE SEMANTIC SYSTEM
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McCarthy & Warrington 1988
Damage to the Verbal Semantic System
TOB Pictures Words
identification task % correct % correct
Living things 94 33
Inanimate things 98 89
• TOB suffered from a progressive disorder of semantic memory
that affected his ability to comprehend spoken names of
animals (except for superordinate category: “it‟s an animal”)
but spared his knowledge of named objects.
• He was able to give good definitional and associative
information about visually presented stimuli, irrespective of
their semantic category.
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in McCarthy & Warrington 1994
Damage to the Visual Semantic System
PHD Pictures Words
identification task % correct % correct
animals 33 77
foods 100 96
• PHD sustained a severe closed head injury, leaving him with a
disproportionate impairment in recognizing visually presented
animals and in matching animal identity (2 different pictures of
caws) relative to objects.
• PHD was normal on the object decision task, and better when
instead of pictures he was asked to define spoken words.
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• Associative visual agnosia can be interpreted in terms of a damage of the visual semantic system
• This framework does not clearly account for a difference between the SDS and semantic system
Shallice,1988; McCarthy & Warrington 1994
VISUAL ASSOCIATIVE A. & MULTIPLE
SEMANTIC SYSTEM
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INPUT
Associative
Agnosia
OUTPUT
V
I
S
U
A
L
V
E
R
B
A
L
hammer
/ hammer /
X
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ORGANISATION OF SEMANTIC
KNOWLEDGE (ALLPORT, 1985)
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• There is only one abstract representation of a given concept
• One can access it from different modalities (visual, verbal, tactile etc.), after a pre-semantic processing (SDS)
• There are different modality-specific outputs
(Riddoch et al. 1988; Caramazza et al. 1990)
AMODAL SEMANTIC SYSTEM
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• Within this framework, visual associative
agnosia corresponds to a deficit in
accessing a unitary semantic system
from the visual modality only
• The SDS is held to be intact:
– i.e. normal performance on the Object
Decision and Head Test (e.g. patients JB).
VISUAL ASSOCIATIVE A.
&
AMODAL SEMANTIC SYSTEM
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Structural Description System
INPUT
SEMANTIC
SYSTEM
Presemantic
Deficit
Associativa Agnosia
(access deficit)
OUTPUT
visual/tactile/auditory
visual/tactile/auditory X
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OPTIC APHASIA (Freund 1889) • The patient showed a deficit in confrontation naming of objects •
• In contrast, he could name them when they were presented in other modalities (tactile, on definition, characteristic sound) and he seemed to have preserved semantic knowledge about objects
• Lesion → Left Occipital + Splenium of Corpus Callosum
• Anatomical explanation → the visual processing is carried out in the spared RH which is disconnected from speech areas in the LH
LH RH
W
area
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VISUAL VS VERBAL SEMANTICS
Lhermitte & Beauvois 1973; Beauvois 1982
• The functional breakdown in OA patients is between the visual semantic system and the verbal semantic system:
• visual semantic system is intact as demonstrated by the preserved ability to perform semantic associative matching tasks and to pantomime the use of objects (i.e. no apraxia)
• verbal semantic system is also intact since naming from other modalities is normal
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INPUT
Optic Aphasia
OUTPUT
V
I
S
U
A
L
V
E
R
B
A
L
hammer
/hammer/
X
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– Differently from associative agnosics, OA patients perform normally on tasks tapping visual semantic knowledge (matching, categorization)
– AO patients can recognize the objects as suggested by their spared ability to show how they would use them
– They are not sensitive to the quality of the stimulus (i.e. real objects are better recognized than line-drawings), as visual agnosics are
– They do not have difficulties in coping with everyday life as agnosic patients have
VISUAL AGNOSIA & OPTIC APHASIA
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• APPERCEPTIVE A.
• Stroke of the posterior cerebral artery affecting visual associative areas bilaterally (sparing the primary visual area, BA 17)
• Tumor lesions of the occipital cortex
• Traumatic focal lesions of the occipital cortex
• Post-anoxic syndromes
- carbon monoxide intoxication
- hart attack
• Degenerative pathologies
- AD and focal, slowly progressive dementias
ETIOLOGY AND BRAIN CORRELATES OF
VISUAL AGNOSIAS
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• INTEGRATIVE A.
• Stroke of the posterior cerebral artery affecting the temporo-occipital cortex bilaterally (including lingual & fusiform gyri)
• PERCEPTUAL CATEGORIZATION
• Stroke of the middle artery involving the parietal cortex in the right hemisphere
• ASSOCIATIVE A.
• Stroke of the left posterior cerebral artery that supplies the occipito-temporal cortex
• Bilateral stroke of the medial occipito-temporal cortex (unusual)
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CATEGORY-SPECIFIC DEFICITS
• After brain damage, the ability to identify exemplars that belong to living categories (fruits, vegetables, animals etc.) or to non-living categories (tools, vehicles, clothes etc.) can result selectively affected
First observations:
• Nielsen (1937)
• Mc Crae & Trolle (1956)
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Warrington & Shallice (1984)
• Described 2 patients with a selective identification deficit as affecting animals, foods and plants, but still able to recognize inanimate objects
• Many other cases followed: e.g.Sartori & Job 1988, Silveri & Gainotti 1988, Farah et al. 1989
• The opposite dissociation, i.e. a selective identification deficit of inanimate objects and spared recognition of biological exemplars has been observed too, but less frequently
• e.g. Hillis & Caramazza 1991; Sacchett & Humphreys 1992; Warrington & McCarthy 1994
Living vs Non Living Categories
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The Sensory/Functional Theory Warrington & Shallice (1984)
• There are two semantic subsystems, one for concepts about living exemplars, the other for non-living ones:
– the former deals with sensory features, the other with functional features
• Living things are better characterized by sensory features and manmade objects are better characterized by their functions and their manner of usage
• Damage to the sensory subsystem leads to a deficit in identifying LT, whereas a damage to the functional subsystem leads to a deficit in identifying NLT
SOME THEORETICAL ACCOUNTS
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THE DOMAIN-SPECIFIC HYPOTHESIS
Caramazza & coll.
• The evolutionary pressures have resulted in specialized (and functionally dissociable) neural circuits dedicated to processing, perceptually and conceptually, different categories of objects
• This applies only to those categories for which rapid and efficient identification could have had survival and reproductive advantages
• Plausible candidate categories are „animals‟, „fruit/vegetables‟, „conspecifics‟, and possibly „tools‟
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• Herpes Simplex Virus Encephalitis
– affects the medial temporal cortex unilateral
left or bilaterally (hippocampus included)
– often associated with category specific
deficits for LT
• Semantic dementia
• Alzheimer‟s disease
Acquired disorders of category-specifc
deficits
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Farah (1990)
• In an historical review of the literature, she noted that researchers reported: – Pure deficits in face recognition (prosopagnosia) and in
visual word recognition (alexia)
– No pure agnosia (for objects)
– No alexia and prosopagnosia
• She then proposed a two process-account of vision.
• There are two processing operations that take place in parallel: – coding undifferentiated global forms
– processing of parts-based representations
Objects, Faces, Words
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• She predicted that patients with pure Object
Agnosia or with Prosopagnosia and Alexia but
without Agnosia could not exist
alexia agnosia prosopagnosia
Pure agnosia
• Rumiati et al 1994; Humphreys & Rumiati 1998
Prosopagnosia and Alexia without Agnosia
• Buxbaum et al 1996; De Renzi & Di Pellegrino 1998
Farah was wrong
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BATTERIES FOR ASSESSING VISUAL
OBJECT AND SPACE PERCEPTION
BORB (Riddoch & Humphreys, 1993)
Birmingham Object Recognition Battery
VOSP (Warrington & James, 1991)
Visual Object and Space Perception Battery
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EARLY VISUAL PROCESSING
Benton Test object
early visual processing
image viewer-dependent
image object-centered
(episodic structural description)
structural description system
semantic knowledge
output phonological lexicon
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FROM VIEWER-DEPENDENT TO OBJECT-
CENTERED REPRESENTATION
Matching unusual views
object
early visual processing
image viewer-dependent
image object-centered
(episodic structural description)
structural description system
semantic knowledge
output phonological lexicon
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STORED STRUCTURAL DESCRIPTION Object Decision
object
early visual processing
image viewer-dependent
image object-centered
(episodic structural description)
structural description system
semantic knowledge
output phonological lexicon
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SEMANTIC SYSTEM
• On visual presentation
–Confrontation naming (semantic errors)
–Pantomiming the use of objects
–Sorting items into categories
–Semantic matching tasks • Which 2 items are used together
• Which 2 items are found together
• Which 2 items are associated sem.
–Questions concerning different aspects of semantic knowledge (Capitani, Laiacona etc.).
object
early visual processing
image viewer-dependent
image object-centered
(episodic structural description)
structural description system
semantic system
output phonological lexicon