Agnosias & Semantic Deficits
Raffaella Ida Rumiati
Cognitive Neuroscience Sector
SISSA
Trieste, Italy
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
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
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
COPYING LINE DRAWINGS
The patient could copy the items he could not recognize
(Rubens & Benson 1971)
Lissauer‟s Model
• 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
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
Lissauer
• Apperceptive
Warrington & co.
• Pseudoagnosia: sensory
discrimination, shape
detection and discrimination
• Apperceptive: figure-ground,
incomplete drawings,
perceptual categorization
• Associative
• Associative
WARRINGTON & COLLEAGUES
Pseudoagnosia: Shape discrimination
Efron test
Pseudoagnosia: Shape detection
Apperceptive Agnosia
Figure-Ground
Ghent overlapping figure test
Apperceptive Agnosia
Incomplete drawings
Gollin‟s test
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
Lissauer
Warrington & Co.
• Pseudoagnosia
• Apperceptive
• Apperceptive:
figure-ground,
completion,
perceptual
categorization
• Associative
• Associative
Humphreys & Co.
• Appreceptive:
• Integrative
agnosia:
– inability to group and
integrate parts of an
object into a
coherent whole
• SDS
• Semantic
System
Humphreys & Co.
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
DIFFERENT TYPES OF ASSOCIATIVE A.
•
•
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
How to assess the SDS
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
Testing the Semantic System
–
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
Picture-to-Picture Matching
Pyramid & Palm Tree Test
Word-to-Word Matching
Pyramid & Palm Tree Test
pine tree
life preserver
pyramid
tulip
palm tree
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?
Barbarotto et al. 1996
SDS & Semantic System
•
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
ASSOCIATIVE A. & SEMANTIC SYSTEM
• 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.)
MULTIPLE SEMANTIC SYSTEM
• 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
Damage to the Verbal Semantic System
TOB
identification task
Living things
Inanimate things
Pictures
% correct
94
98
Words
% correct
33
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.
McCarthy & Warrington 1988
Damage to the Visual Semantic System
PHD
identification task
animals
foods
Pictures
% correct
33
100
Words
% correct
77
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.
in McCarthy & Warrington 1994
VISUAL ASSOCIATIVE A. & MULTIPLE
SEMANTIC SYSTEM
• 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
INPUT
hammer
Associative
Agnosia
OUTPUT
V
I
S
U
A
L
X
V
E
R
B
A
L
/ hammer /
ORGANISATION OF SEMANTIC
KNOWLEDGE (ALLPORT, 1985)
AMODAL SEMANTIC SYSTEM
•
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)
VISUAL ASSOCIATIVE A.
&
AMODAL SEMANTIC SYSTEM
•
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).
INPUT
Presemantic
Deficit
Structural
Description System
X
SEMANTIC
visual/tactile/auditory
Associativa
Agnosia
(access deficit)
SYSTEM
visual/tactile/auditory
OUTPUT
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
W
area
LH
RH
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
INPUT
Optic Aphasia
OUTPUT
hammer
V
I
S
U
A
L
X
V
E
R
B
A
L
/hammer/
VISUAL AGNOSIA & OPTIC APHASIA
– 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 linedrawings), as visual agnosics are
– They do not have difficulties in coping with everyday
life as agnosic patients have
ETIOLOGY AND BRAIN CORRELATES OF
VISUAL AGNOSIAS
• 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
• 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)
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)
Living vs Non Living Categories
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
SOME THEORETICAL ACCOUNTS
The Sensory/Functional Theory
Warrington & Shallice (1984)
• There are two semantic subsystems, one for
concepts about living exemplars, the other for nonliving 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
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‟
Acquired disorders of category-specifc
deficits
• 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
Objects, Faces, Words
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
Farah was wrong
• 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
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
EARLY VISUAL PROCESSING
object

early visual processing

image viewer-dependent

image object-centered
(episodic structural description)

structural description system

semantic knowledge

output phonological lexicon
Benton Test
FROM VIEWER-DEPENDENT TO OBJECTCENTERED REPRESENTATION
object

early visual processing

image viewer-dependent

image object-centered
(episodic structural description)

structural description system

semantic knowledge

output phonological lexicon
Matching unusual views
STORED STRUCTURAL DESCRIPTION
object

early visual processing

image viewer-dependent

image object-centered
(episodic structural description)

structural description system

semantic knowledge

output phonological lexicon
Object Decision
SEMANTIC SYSTEM
object
• On visual presentation

early visual processing

image viewer-dependent

image object-centered
(episodic structural description)

structural description system

semantic system

output phonological lexicon
–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.).