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

The patient could copy the items he could not recognize

(Rubens & Benson 1971)

COPYING LINE DRAWINGS

• 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

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

• Associative

Warrington & co.

• Pseudoagnosia: sensory discrimination, shape detection and discrimination

• Apperceptive: figure-ground, incomplete drawings, perceptual categorization

• 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

• 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

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.

• 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.

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

– 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

Picture-to-Picture Matching

Pyramid & Palm Tree Test

Word-to-Word Matching

Pyramid & Palm Tree Test

pine tree life preserver

tulip palm tree

pyramid

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?

• 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

• 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

• 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

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.

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.

• 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

INPUT

Associative

Agnosia

OUTPUT

V

I

S

U

A

L

V

E

R

B

A

L

hammer

/ hammer /

X

ORGANISATION OF SEMANTIC

KNOWLEDGE (ALLPORT, 1985)

• 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

• 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

Structural Description System

INPUT

SEMANTIC

SYSTEM

Presemantic

Deficit

Associativa Agnosia

(access deficit)

OUTPUT

visual/tactile/auditory

visual/tactile/auditory X

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

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

V

I

S

U

A

L

V

E

R

B

A

L

hammer

/hammer/

X

– 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

• 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

• 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)

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

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

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‟

• 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

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

• 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

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

Benton Test object

early visual processing

image viewer-dependent

image object-centered

(episodic structural description)

structural description system

semantic knowledge

output phonological lexicon

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

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

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