semantic memory and brain lesion studies have shown that two primary brain regions are associated...

Semantic memory and brainSemantic memory and brain

• Lesion studies have shown that two primary brain regions are associated with semantic impairment– Left prefrontal cortex– Temporal lobes

See Martin & Chao (2001), 194-201, Cognitive Neuroscience for further information

Semantic memorySemantic memory


• Structure of semantic representation– Neurologists have proposed for some time that

an object is represented in terms of the sensory and motor attributes that were acquired from experience with the object either by perceiving the object or by acting on the object (e.g., tool)


• Structure of semantic representation– Thus, an object may be represented by a

distributed network of brain regions representing the sensory, motor, and functional attributes for that object

– E.g., colour, form, function, and motor attributes may be represented by those brain regions associated with the perception or motor production


• Structure of semantic representation– It has been shown that asking participants to

generate the name of action activated posterior regions of the middle temporal gyrus just anterior to the site active during motion perception


• Structure of semantic representation– Chao and Martin (2000) showed that when

participants viewed manipulable objects (e.g., hammer) a circuit involving the left posterior parietal lobe and the left ventral premotor area became activated, but these areas were not activated when buildings, animals, and faces were presented


• Structure of semantic representation– Many studies have shown that modality-specific

regions become active as other types of category knowledge are processed

– E.g., color, shape, and motion properties of category knowledge are processed near the respective brain regions that are involved in perceiving these attributes (see next figure)

Martin & Chao (2001). Current Opinion in NeurobiologyMartin & Chao (2001). Current Opinion in Neurobiology

(a) Ventral brain regions from occipital to temporal lobes—represent color and shape properties

(b) Left lateral areas– motor areas in prefrontal cortex and parietal areas represent manipulation of objects; posterior temporal lobes represent motion properties of objects


• Structure of semantic representation– Weisberg et al. (2007) trained people in the use

of novel tools– Behavioral results showed that with extensive

training participants became more skilled in their use of novel tools

Semantic memory and brainSemantic memory and brain• Structure of semantic representation

– fMRI scanning -- participants matched pictures of novel tools before and after training

– fMRI findings showed that after training similar brain regions were activated with novel tools that previous research studies have shown are activated with familiar tools

Semantic memory and brainSemantic memory and brain• Structure of semantic representation

– Regions of activation wereMiddle temporal gyrus – motion of objectInferior parietal sulcus and premotor area of PFC –

tool manipulationFusiform gyrus (ventral temporal lobe) –

appearance of object

Semantic memory and brainSemantic memory and brain• Conclusions

– Functional experience with novel objects changed their brain representation

– Novel brain region activation similar to that observed with familiar tools

– Findings suggest there is a specialized circuitry for learning about the specific sensory and motor-related properties of objects

– This circuitry was activated when perceiving an object; suggests that one function of this circuitry is object perception

Semantic memory and brainSemantic memory and brain• Conclusions

– Further research needed to determine what aspects of experience (training) is required to acquire tool-like object representation (e.g., observation)

Alzheimer’s diseaseAlzheimer’s disease

• Alzheimer’s disease– cortical, progressive dementia– disease is associated with the development of

neuro-fibrillary tangles and plaques


• deficit in two or more areas of cognition, at least one of which is memory

• interferes with social or occupational functioning

• decline from premorbid level

• gradually progressive course

• rule out other causes


• Alzheimer’s disease– three types of memory problems

episodic memory impaired (e.g., free recall)executive function (WM of Baddeley appears to be

affected)semantic memory is also impaired

– note: pure amnesics do not have the latter two impairments


• AD– semantic memory

system for storing, organizing, and manipulating information pertaining to the meaning of words, concepts, and their associations

conceptualized as a broadly distributed networkenables judgments about the properties and

functions of items


• naming and word generation to semantic cues both require semantic memory, both impaired in AD

• Explanations:– degradation of the semantic network?– loss of access to preserved concepts?– both?

Putting it together: Component process model of memory

Putting it together: Component process model of memory

• General assumptions of model– Moscovitch believes that memory is not unitary

but depends upon the operation of different independent components

– this model distinguishes between modules and central systems

Component process model of memory


• General assumptions of model– this model postulates that the same modules

mediate implicit domain-specific perceptual tests of knowledge and perceptual repetition priming testse.g., prosopagnosics who respond differentially to

familiar versus unfamiliar faces on implicit tests show normal repetition priming effects

e.g., dyslexics who have an intact word-form system show preserved repetition priming effects



• Overview of model– 4 components– nonfrontal neocortical component made up of

perceptual and semantic modules that mediate performance on item-specific implicit memory tests

– basal-ganglia component that mediates performance on sensorimotor tests of memory



• Overview of model– 4 components

medial-temporal/hippocampal component that mediates explicit memory tests that are cue/dependent or associative

central-system frontal-lobe component that “works with memory” and mediates performance on strategic explicit tests



• Modules and central systems– modules are computational devices that have

propositional content and specify three criteria:domain specificityinformation encapsulationshallow output



– domain specificityinformation that a module processes is restrictedimplies that it should be possible to damage this

system selectively both functionally and neuroanatomically



– information encapsulationprocessing operations of the system are not

accessible to higher level functionsit is difficult for higher level functions to modify

the processing by the systemimplies that it should be possible for modular

functions to process information effectively even when there is general intellectual decline (e.g., AD)



– shallow outputoutput has no meaning other than that assigned to

ite.g., a person with an associative agnosia is quite

capable of drawing a viewed object, but cannot name the object, describe its function etc.

Sirigu (1991) reported a patient FB with an associative agnosia could appropriately manipulate unidentified objects whose function could not be described



• Examples of modules– word form recognition system – face-recognition system– phonological-word-form system



– Central systemscentral systems integrate information from

different dissimilar domainsthe processing carried out by central systems can

be influenced by other processesthe information may be accessible to

consciousnessthe output of central systems is meaningful



• Moscovitch next classifies memory tests using the conceptual framework just presented– caveat -- no test is process pure (Jacoby, 1991)



• Implicit tests– item specific: perceptual, conceptual– procedural: sensorimotor, ordered/rule-based

• Explicit tests– Associative– Strategic



• Implicit tests: item specific, perceptuale.g., identification of fragmented words or pictures

– hypothesized processwhen stimulus presented, it is processed by

cortical presemantic modules that transform the stimulus into presemantic structural representation

this output is then delivered to central system structures for semantic interpretation



• Implicit tests: item specific, perceptual– the modules that processed the stimulus and the

central structures that interpreted the stimulus are modified by the stimulus leaving a perceptual and semantic record

– reactivation of this record is the basis of perceptual and conceptual priming effects respectively



• Implicit tests: item specific, perceptual– anatomical localization– perceptual modules are in the posterior

neocortex– evidence (negative)

amnesics show normal perceptual primingdamage is in the medial temporal lobes and

related structures in the diencephalon



• Implicit tests: item specific, perceptual– evidence (positive)

apperceptive versus associative agnosicsapperceptive agnosics: have relatively intact

sensory processes (e.g., colour, acuity, motion)however, they cannot form a percept of the objectfor example, they are unable to recognize, copy, or

match simple shapes



• Implicit tests: item specific, perceptual– evidence (positive)

apperceptive versus associative visual agnosicsassociative agnosics can copy, recognize, and

match objects, but are unable to recognize the identity of an object

apperceptive agnosics tend to have damage in the bilateral regions of the occipital lobes

associative agnosics tend to have damage in the ventral regions in the anterior temporal lobes



• Conceptual repetition effects and semantic records– in conceptual repetition tests, the target item is

not repeated at test– the target is elicited by a semantic cue (e.g., a

related word or question)e.g., generate exemplars of category cues



• Conceptual repetition effects and semantic records

this model postulates that conceptual repetition effects are mediated by central systems, which interpret the output from a perceptual module, and store a semantic record of their activity

model predicts that modality and format should not affect conceptual repetition effects, but that levels of processing should

these predictions have been confirmed



• Conceptual repetition effects and semantic records

Conceptual repetition effects have been reported in individuals with amnesia



• The hippocampal component: A module for episodic, associative memory– conscious recollection of episodes in which the

cue is sufficient for retrieval (e.g., simple recognition and cued recall)



• The hippocampal component: A module for episodic, associative memory– hippocampal structure consists of a circuit

consisting of: hippocampus, parahippocampal gyrus, entorhinal cortex, perirhinal cortex, mammilary bodies, dorsomedial nucleus of the thalamus, the cingulate cortex, and the fornix

– amnesia is associated with bilateral damage of these structures



• The hippocampal component: A module for episodic, associative memory– how it works

the input modules and central system deliver their output to working memory

the contents of working memory are accessible to consciousness

the domain of the hippocampal component is consciously apprehended information (ie the information processed by the hippocampal component)




hippocampus binds or integrates the output from the modules and central systems that contributed to the conscious experience

the bound engram (memory trace) is encoded as a file entry in the hippocampal complex




ecphory or conscious retrieval occurs when a cue (external or internal) automatically interacts with a memory trace

encoding and retrieval (ecphoric) processes are automatic, obligatory, cognitively impenetrable, and informationally encapsulated because this component is modular

How episodic memory worksHow episodic memory works

Conscious Awareness

Encoding/Ecphory

Control systems



• Frontal lobes: central systems and strategic explicit tests– frontal lobes critical in memory tests in which

extracue strategic factors are critical– e.g., free recall (esp. categorized FR), memory

for temporal order



• Frontal lobes: central systems and strategic explicit tests– prefrontal cortex is a large heterogeneous

structure consisting of several distinct areas, each with its own projections to and from different brain regions, and with its own functione.g., dorsolateral versus orbital regions



• Frontal lobes: central systems and strategic explicit tests– the frontal lobes postulated to play a critical role

during encoding byits selection of memory strategiesby organizing input



• Frontal lobes: central systems and strategic explicit tests– during retrieval the frontal lobes play a critical

role byorganizing output from hippocampal componentdetermining its temporal orderorganizing mnemonic searches



• Frontal lobes: central systems and strategic explicit tests

e.g., What were you doing last Friday?

– Frontal lobesnot critical for storage and retention of information

(hippocampal)critical in those aspects of memory requiring

organizational and strategic processing



• Frontal lobes: central systems and strategic explicit tests– Moscovitch refers to this function as working-

with-memory (it is theoretically close to the central executive of Baddeley’s working memory model



• Procedural implicit tests– two general categories distinguished

sensorimotor and ordered/rule based

– sensorimotorimprovement of motor or sensory skillse.g., pursuit rotor, mirror drawing, reading

transformed script

– ordered/rule basede.g., Tower of Hanoi



• Procedural implicit tests– sensorimotor

basic assumption of model: acquisition and retention of motor skills result from modification of structures involved in performing the task

performing a task leaves behind a sensorimotor record

reactivation of a sensorimotor record accounts for performance on implicit tests of memory




these assumptions have at least two testable implications

first, deficits should be observed in people with damage to sensorimotor structures no matter how well preserved their intellect is

patients with amnesia should have preserved sensorimotor function




studies have shown that patients with AD have normal pursuit rotor function (Jacobs, 1999)

patients with amnesia have normal pursuit rotorpatients with Huntington’s and Parkinson’s

disease have impaired pursuit rotor learning

– Rule learning see article



• Implications of model– perceptual priming is a consequence of

reactivation of perceptual-input modules is supported byfinding of modality-specific priming effectsfinding of strong format effectsfinding that levels of processing effects have

negligible effects on perceptual tests (recall perceptual-input modules are presemantic)



• Implications of model– perceptual priming is a consequence of

reactivation of perceptual-input modules is supported byfinding that perceptual priming effects are little

affected by dividing attention (recall modules are hypothesized to operate automatically)



• The hippocampal module: Implications and comparisons with other models– Is hippocampally-based memory spatial, conscious

or both?– Nadel has proposed that the hippocampus is

specialized for dealing with spatial information– Moscovitch has claimed that the hippocampus

binds together any information that is consciously apprehended



• The hippocampal module: Implications and comparisons with other models– note: Moscovitch uses the term consciousness

interchangeably with phenomenological awareness– ie the individual is aware of having experienced a

stimulus previously– Moscovitch argues that the memory trace includes

the contents of consciousness as well as the elements that make experience conscious



– Conscious recollection, thus is a property of the memory trace

– Cognitive resources: differential effects on central frontal systems and hippocampal systemsMoscovitch postulated that dividing attention

should have differential effects on memory tasks that are mediated by hippocampally versus frontally

strategy: select tasks known to be affected by frontal damage, and evaluate whether they are impaired by dividing attention

semantic memory and brain lesion studies have shown that two primary brain regions are associated...

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semantic impairment

ventral brain regions

similar brain regions

primary brain regions

respective brain regions

brain lesion studies

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