Category-Specific Deficits
and Implications for the
Structure of Conceptual
Knowledge
David Price
Basic Facts/Trends
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Distinguishing features of category-specific deficits:
Patients seemingly exhibit disproportionate and selective
impairment of knowledge of one category of objects v. other
categories
Most studies of instances of category-specific deficits involve
sparing or selective impairment of ‘living things’, ‘non-living
things’, ‘animals’, ‘fruits/vegetables’, and ‘artifacts’
Unclear as to whether instances of category-specific deficits are a
result of damage to a categorically-organized semantic system, or
damage to specific modality of knowledge (e.g. visual or
functional)
The Basic Motivation
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Scientific explanation of category-specific deficits center around the
basic question of Q1: How is conceptual knowledge
organized?
Cognitive Neuropsychology attempts to answer Q1 by examining
cases of individuals who seem disproportionately impaired at
naming, defining, and/or characterizing members of a given
category, and do not exhibit similar deficits in other categories. (e.g.
S can’t name any x’s that are animals, but can name all other x’s of
category <living things>)
If cognitive scientists can accurately predict the cause and nature of
cases of category-specific impairments, then a theoretical backdrop
for a cognitive theory of conceptual knowledge could emerge
Methodology of this presentation
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Give brief summary and history of categoryspecific deficits
Discuss two competing theories of categoryspecific deficits (Sensory/Functional Theory v.
Domain-Specific Theory)
Discuss these in terms of particular cases
which purported to support them
Discuss explanatory inconsistencies for both of
the theories, discuss soundness of their
respective presumptions
History of the Condition
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First clear example: Warrington & Shalice (1984) describe 4
patients recovering from herpes simplex encephalitis that appear
disproportionately impaired at both comprehension and naming of
living things v. nonliving things
W & S (1984) also observed case of brain-damaged individual
w/reverse dissociation (i.e. nonliving things were problematic, but
living things were not)
W & S inferred from these 5 instances that selective brain damage
could result in category-specific semantic deficits
Thus, a study of the nature of category-specific semantic deficits
would prove fruitful for the study of the structure of semantic
knowledge in normal subjects
History of the Condition (con’t)
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All 4 cases showed disproportionate difficulty for living vs. nonliving
things
J.B.R. reported as unable to recognize/name 2/48 living things
(animals or plants) but could describe/named 45/48 nonliving
things
S.B.Y. identified 0/48 living things but identified 36/48 nonliving
things
Subsequently, confirmation of dissociation b/w living v. nonliving
things obtained in many other studies of brain-damaged subjects
(variance in etiology; herpes simplex encephalitis, trauma, cerebrovascular accident, neurosurgery)
Reverse dissociation also confirmed: impaired performance nonliving
objects v. spared ability with living things
Basic Methodological Assumptions/Practices
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(a)
(b)
Picture-naming task necessarily involves activation of semantic
information about a particular object (usual method is to use
Snodgrass and Vanderwart picture set)
Comprehension tests: administered after picture-naming task,
these tests involve the individual’s ability to distinguish features of
objects; are meant to demonstrate either:
that the individual’s problem results from the inability to
recognize the problem-object, in which case the relevant
system is not at all presented with the necessary features to
produce the desired output -ORThat the individual’s problem results from an inability to
properly extract properties of the problem-object which are
somewhere present in the system (the latter seems more likely, given
the lack of instances in which a subject’s dissociation is necessary; i.e. it is
not the case that S cannot properly identify all entities of category c, it is
that he cannot properly identify all entities in category c effectively, or
consistently, or functionally)
Is the semantic system organized
categorically?
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Hypothesis that the semantic system is categorically organized
initially not seriously entertained
Inconsistent findings for category hypothesis from initial cases
usually manifest in that patterns of affected semantic categories
failed to correspond to definite categorical distinctions
Reasons for initial rejection:
If semantic system is categorically organized, then JBR’s categoryspecific deficit should correspond to definite semantic categorical
distinctions, like living v. nonliving
JBR’s deficit is in animal & plant categories (living) AND food
category (nonliving)
Thus, hypothesis that semantic system is categorically organized is
violated
Proposal of Sensory/Functional Theory of Categoryspecific deficits
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Refutation of hypothesis that semantic system is categorically organized
lead Warrington & Shalice (1984) to propose Sensory/Functional theory
This theory says that JBR and SBY’s case can be explained by accounting
for damage to visual semantic subsystem and/or damage to functional
semantic subsystem
Visual semantic subsystem: damage to this area results in
disproportionate deficit of living things and foods because the identification
of both contingent on visual features
Functional semantic subsystem: damage to this area results in
disproportionate deficit of nonliving things because nonliving things are
distinguished based on utility or function.
THUS, apparent categorical nature of semantic deficits doesn’t reflect
categorical structure of semantic knowledge, but reflects instead a more
basic organizing principle of semantic system contingent on sensory and
functional cues
Sensory/Functional Theory
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2.
Principle
Non-categorical,
modality-specific
organization
Differential attribution of
living v. nonliving things
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Explanation
Semantic system organized
into modality-specific
subsystems
(visual/perceptual,
functional/associative)
Ability to recognize/name
living things contingent on
visual/perceptual info.; nonliving things contingent on
functional/associative info.
Case Study 1: Bert (Barry & McHattie)
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Barry & McHattie case study supports Sensory/Functional
Theory
Bert, age 74, had stroke which caused right visual field defect, no
problems with conversation, intellectually intact, preserved
comprehension
Complained of both word-finding difficulties and pronounced
inability to name entities in the category of animals
Barry and McHattie wanted to explore possibility of category-specific
anomia for animals
Initial testing: appeared to have intact object recognition (verified
by appropriate use of household items and by his performance of a
test which tested object recognition; shown 3 different pictures, had
to indicate by pointing which of the three pictures had objects which
contained items with the same name, otherwise 2 things of same
name but different physical appearances)
Bert con’t
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Picture naming task: Bert presented with 100
line drawings of Snodgrass and Vanderwart test
Either produced correct name of the picture, or
indicated he couldn’t say it and would
subsequently partake in some degree of
description
For instances in which Bert could not name it, he
indicated too that he ‘knew the thing’.
Results of Picture Naming
Success rate:
(a) Animal naming=12%
(b) Fruits/vegetables
naming=47%
(c) Musical instruments=
50%
(d) Tools=60%
(e) Vehicles=67%
(f) Articles of clothing=71%
(g) Body-parts=100%
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Worst at naming animals as
compared to any other
category
Data does not fit hypothesis
that semantic knowledge
organized into discrete
categories
Word familiarity, visual
complexity of pictures, and
age-of-acquisition did effect
Bert’s responses for the task
(e.g. Bert was better at
naming familiar items vs. nonfamiliar)
Possible Reasons for Bert’s Deficit
Reasons
(a) Inability to recognize
animals
(b) Problematic integrity of
semantic representation
of animal, or problem
with the utilization of
those representations
which support proper
naming
Explanation
(a) refuted, Bert could point
to appropriate animal in
a picture of two related
animals when prompted
by an animal name
(b) Possible, comprehension
test follows to seek out
this possibility
Comprehension Test
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4 questions for each of the 30 animals + 30 items presented to
Bert:
One required ‘yes’ response about category of the item (e.g. Is a
squirrel an animal?)
One contained false information about category of object (e.g. is a
mushroom a musical instrument?)
One was a correct question about physical appearance of item of
category (e.g. has a squirrel got a bushy tail?)
One was false question about physical appearance (e.g. has a
squirrel got wings?)
Results of Comprehension Test
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Type of Question
1) Category Questions
2) Physical Property
Questions
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Results
1) 93.3% correct for
category questions
2) 76.7% correct for
questions about physical
properties
*significant difference b/w 1 and 2, thus his category-specific
problem is a reflection of a failure to account for physical
properties which distinguish members of animal category from
members of other categories
**Thus, Bert’s inability to name and recognize members
of the animal category is because of a malfunctioning
visual semantic subsystem, according to
Sensory/Functional Theory
Problems for the Sensory/Functional Theory
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Because this theory assumes that ability to recognize all living things
differentially contingent on info internal to the same
visual/perceptual subsystem, prediction is that a dissociation will not
be observed within same category ‘living things’.
CONTRARY to this is the report of individuals with disproportionate
deficits for ‘fruits/vegetables’ v. ‘animals’
Predicts patients will present w/disproportionate deficits for type of
info upon which successful recognition of impaired category is
assumed to depend on. Early reports supported this, but data has
been criticized on methodological grounds (pictures unmatched for
word frequency et cetera)
Predicts association b/w disproportionate deficit for type of
knowledge & disproportionate deficit for category of objects that
depends on that knowledge.
CONTRARY to this: patients reported w/ disproportional deficit in
functional/associative knowledge but no associated disproportionate
deficit for living things v. non-living things
Domain-Specific Hypothesis
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Central assumption: evolutionary pressures resulted
in specialized neural circuits dedicated to processing
(both conceptually and perceptually) distinct
categories of objects. Instantiates the notion that
semantic system may be organized categorically.
(Warrington, 1981)
Provides independent specifications for how we can
characterize a conceptual category; restricted only to
categories that were advantageous with respect to
survival and reproductive advantages
Domain-Specific Hypothesis con’t
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Predictions:
If there are distinct neural systems dedicated to categories of
‘animals’, ‘fruits/vegetables’, and possibly ‘tools’, then it’s impossible
for function of one system, if damaged, to be recovered by other
systems (i.e. predicts poor-recovery of impaired performance
No necessary correspondence b/w deficit for knowledge of modality
x and conceptual deficit for category of objects
Patients might present category-specific visual agnosia. This follows
from assumption that perceptual stages of object recognition are
possibly functionally organized according to domain-specific
restrictions. (supported by observation of subjects with equal
deficits to visual and functional knowledge of living things, but
visual agnosia for living things v. non-living things)
Case 2: Patient EW (Caramazza and Shelton, 1998)
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This case is purported to support the Domain-Specific
Hypothesis (Caramazza and Shelton, 1998)
Patient EW: selective deficit for category of animals,
equally impaired for visual and functional attributes of
members of animal category v. other living things and
artifacts
E.W. tested via Picture Naming, Sound Identification,
Object decision, Parts decision, Visual processing, and
Central-Attribute judgments
Picture Naming
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Snodgrass & Vanderwart picture set, matched for
familiarity and frequency
EW disproportionately impaired at naming animals
(55%) v. non-animals (82%). Controls were 100% at
naming animals and 98% for non-animals
EW’s performance both quantitatively and qualitatively
different for animals v. non-animals. Animals, EW either
named picture incorrectly or did not recognize picture;
for non-animals, EW recognized the picture but couldn’t
retrieve name
EW’s deficit did not extend to other living things like the
category ‘fruit/vegetables’ (performed very well in this
category)
Sound Identification
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Task presented E.W. with 32 characteristic sounds of
animals and 32 non-animal sounds
E.W. impaired at naming animals v. non-animals based
on characteristic sound (25% correct v. 63%)
This indicates that naming impairment is not restricted
to one sensory system
Object Decision
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Asked to decide ‘yes’ or ‘no’ whether depicted object was
real.
Performance on this task is interpreted as reflecting
integrity of visual/structural description system (this was
system purported to be one of the causes of Bert’s
naming problems)
Significantly below normal range for differentiating b/w
real from unreal animals (60% correct, controls were
90%)
Within normal range for distinguishing real from unreal
non-animals (92% correct, controls were 84%)
Parts Decision Task
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EW to decide which of two heads went with
headless body
Severely impaired on this task for animals (60%,
controls were 100%)
Normal range for artifacts (97%, controls were
97%
Indicates that EW doesn’t have deficit for visual
processing for complex stimuli
Suggests her impairment for objects reality
decision for animals is categorically based
Central-Attribute Judgments
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EW asked to decide if a given attribute was true of a given item.
This tests ability to distinguish properties/features of an object
Severely impaired for attributes pertaining to animals (65%,
controls were 85-100%)
Normal range for attributes pertaining to non-animals (95%,
controls were 85-100%)
Equivalently impaired for visual/perceptual and
functional/associative knowledge of living things (65% for both)
Normal range for both types of knowledge for non-animals
Thus, EW’s performance on central-attribute questions implies that
her deficit is not restricted to production
Conclusions and Speculations of EW Case
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Results summarized by Caramazza & Shelton:
EW has category-specific deficit restricted to category of animate
objects (this persisted under strict control of nuisance factors like
familiarity, visual complexity, frequency, or combination of them)
Category-specific deficit manifests in visually and auditorily
recognizing animate objects
Category-specific deficit in language comprehension; manifested
in poor performance w/ statements about animate objects v.
normal limits w/statements about other living things and artificats
Domain Specific Organization of Conceptual Knowledge
and Evolutionary Adaptation
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Fact that the categories animals, fruits/vegetables, and artifacts can
be independently impaired suggests that it is the case that ONLY
these three categories form basis for conceptual organization of
conceptual knowledge
This assumption requires independent empirical justification;
recourse to evolutionary adaptation could provide such justification
Recognition of animal category would imply ability to respond
quickly to all types of animals, including predators. Physiological
evidence: we can detect movement of living organisms faster than
movement of non-living things, we require less information
Evolutionary adaptations for recognition of animals and plant life
provides skeletal neural structures which would organize perceptual,
conceptual, and linguistic knowledge modern humans have of these
categories
Domain Specific Organization of Conceptual
Knowledge and Evolutionary Adaptation con’t
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Implication: only true
category-specific deficits are
those which involve categories
of animal, plant-life, and
possibly artifacts
Implication: supposition that
specialized neural mechanisms
are more likely to be
selectively damaged implies
that frequency of categoryspecific deficits for living things
should be higher than nonliving things.
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More specific categories like
tools would not constitute a
category-specific deficit,
because the category of tools
does not serve the function of
organizing semantic knowledge
into categories
This 2nd implication is
supported in that most cases
of category-specific deficits are
manifested in animal or plant
categories (aka,
fruits/vegetables)
Conclusions
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Given that, as it stands now, there is a higher degree of
supporting evidence for domain-specific theory
compared w/sensory-functional theory, domain-specific
theory explains category-specific deficits better
Also, much of the evidence for sensory/functional theory
was thrown out due to fact that uncontrolled stimulus
factors like familiarity could account for apparent deficit
When these factors were controlled, many of the early
cases supporting sensory/functional theory were shown
to have been partially a function of uncontrolled stimulus
factors
Works Cited
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Caramazza, A., & Mahon, B. (2003). The Organization of Conceptual
Knowledge: the Evidence from Category-Specific Semantic Deficits.
Trends in Cognitive Sciences, 7: 8, pp. 354-361
Caramazza A., & Shelton, J. (1998). Domain-Specific Knowledge
Systems in the Brain: The Animate-Inanimate Distinction. Journal of
Cognitive Neuroscience, 10:1, pp. 1-34
Lombardi, L. & Sartori, G. (2004). Semantic Relevance and Semantic
Disorders. Journal of Cognitive Neuroscience, 16:3, pp. 439-452
Warrington, E.K., & Shalice, T. (1984). Category-Specific Semantic
Impairments. Brain, 107, 829-854