M5, T2, Theories/Models of semantic memory Flashcards
How conceptual knowledge is organised/structured
Neural: Conceptual knowledge is organised based on neurally specific areas that store categorical information
Correlated: conceptual knowledge is organised in the brain based on the statistical cooccurrence of different features of objects. Brain damage results in category specific impairments for correlated features
Neural structure principle
Modality specific theories
- Sensory/Functional Theory
- Domain Specific Hypothesis
Correlated structure principle
Statistical cooccurrence
- organised unitary content hypothesis
- conceptual-structural account
Sensory/functional theory of how conceptual knowledge is organised
- Adheres to neural-structure principle
- Information in brain segregated based on types of information (perceptual vs. non-perceptual) (e.g. Allport, 1985; Warrington & Shallice, 1984)
- Information about an object represented in a distributed fashion in brain depends on modality of input
- Allport (1985): each type of sensory information represented in separate interconnected nodes
-> Nodes specific information: action-oriented elements, kinaesthetic elements, visual elements, tactile elements, and auditory elements
Sensory/functional theory - Warrington and colleagues, sensory/functional theory assumes
- Organisation of semantic system based on modality specific sub-systems
- Semantic knowledge is organised into perceptual (sensory) and non-perceptual (functional) information
-> Visual/Perceptual
-> Functional/Associative
Perceptual and non–perceptual information is differentially important for different categories of knowledge
-> Naming living things – visual/perceptual information
-> Naming non-living things – functional/associative information
Sensory/functional theory prediction one - specific deficits should not occur
Prediction 1: Recognition of all living things depends on representations in the same semantic sub-system (visual/ perceptual) therefore….
- Specific deficits within the living things category should not be observed
Yet patients show deficit for
-> fruits/vegetables relative to animals
-> Animals relative to fruits/vegetables
- Warrington & Shallice - deficits outside the living/non-living things ok if these things have emphasis on perceptual properties of an object
Sensory/functional theory prediction 2 - disproportionate deficits for modality
Prediction 2: Patients with category specific deficits (e.g. living vs. non-living) will also have disproportionate deficits for the modality or type of information tapped into via the impaired category (e.g. visual versus functional information)
-> A patient impaired for living things will also be disproportionately impaired for visual/sensory information
-> Problems providing information or knowledge about visual/perceptual characteristics or functional/associative characteristics
- Initially patient data was consistent with the prediction but more recent patient cases do not support this prediction
Sensory/functional theory predictions - patient data relating to pred 2
- Patient data shows that some category specific impairments are associated with impairments for both sensory and functional information for an entire category
-> Patient impaired for non-living things, is equally impaired for sensory and functional knowledge
-> Patient EW’s performance on Central Attribute Task
Sensory/functional theory predictions - implications of patient data on pred 2
Can be argued that visual/perceptual and functional/associative representations are interdependent so damage to one would affect the other to some degree
- Both living and non-living things have perceptual and functional elements
- Damage to one type of information will have some type of impact on the other type of features
Sensory/functional theory predictions - pred 3, categorical deficit aligns with v/p or f/a deficit
- Patients with a deficit for visual/ perceptual or functional/ associative knowledge should show a categorical deficit that is most dependent on that type of knowledge
-> A patient is impaired in visual domain should show greater impairment for living things - Patients have shown greater deficit for visual/perceptual knowledge than functional/associative knowledge but do not show performance differences in naming living and non-living things
Evidence against the sensory/functional theory
- Not well substantiated by patient data
- Predicts damage to perceptual or non-perceptual properties -> damage categories most reliant on this type of information
- Not always the case
-> Patient EW – problem with animals BUT ok fruits, vegies, food, musical instruments
-> Patients problems processing visual information but do not have any category specific processing deficit
Evidence against the sensory/functional theory - Lambon-Ralph et al., (1998), patient IW
- Problem with processing visual information but no associated category-specific deficit in naming comprehension
- Patient IW picture matching when given perceptual versus non perceptual information (e.g. spider, lion, fly, horse, dog)
- IW’s performance worse when given perceptual than non-perceptual information about an object, equivalent performance for living and non-living things (no category deficit)
- When asked questions about items – better at providing non-perceptual information and provided greater amounts of non-perceptual information about an item when asked to provide a definition
Evidence against the sensory/functional theory, priming study
Flores d’Arcais et al (1984; 1985) two studies, very flawed studies
Priming word pairs perceptually (visually similar) but not conceptually related
Paintbrush-carrot = priming, found effects
Pecher et al (1998) – using correct methodology – no priming for perceptually but not conceptually related items e.g., pizza-coin vs. pizza- hotdog
Domain-specific hypothesis
- Assumes evolutionary pressures resulted in specialised and functionally distinct neural circuits that process perceptually and conceptually distinct categories of objects
- Semantic knowledge is organised into categories (domains) that reflect evolutionary salient distinctions
-> Specialised neural mechanisms for recognising and understanding certain categories of knowledge
-> Categories are those which require rapid and efficient identification for survival and reproduction
Evidence to support domain-specific hypothesis
- Accounts for patient data sparing categories of animals, fruits/vegies or body parts or patients with just one category impaired
- Consistent with developmental studies:
-> infants distinguish between living & non-living things
-> 9 month olds – animals vs. non-animals, biological motion vs. non-biological motion
Domain-specific hypothesis predictions, pred 1, dedicated neural systems
Prediction 1: Assumes distinct neural systems dedicated to animals, fruits/vegetables, conspecifics and tools then the other systems cannot compensate for the damaged neural system.
-> Data from 16 year old patient with poorer performance for living than non-living things had this deficit since age 1, and impaired for both visual and non-visual information about living things
-> More patient cases show deficits for living than non-living things
-> Patients with specific-category deficits
Domain-specific hypothesis predictions, pred 2, no association between modality and category
Prediction 2: No association between a deficit for a type or modality of knowledge and a conceptual deficit for a specific category
- For any given category impairment this will be for all types of knowledge within the category
- No differentiation between a modality of knowledge (perceptual/function) and the type of impairment
-> Patients with category-specific semantic deficits present with equivalent impairments to visual/ perceptual and functional/ associative knowledge
Domain-specific hypothesis, pred 3, perceptual stages and domain specific constraints
Perceptual stages of object recognition models might be functionally organised by domain specific constraints and this predicts category specific visual agnosia despite intact early visual processes
-> Supported by patients who have equivalent impairments in their performance on tasks testing visual/perceptual and functional/ associative conceptual knowledge for living things BUT visual agnosia for living things compared to non-living things
Problems with domain-specific hypothesis
- Lack specificity how knowledge is represented within categories
- Selective deficits -> categorical organisation but approach does not explain how things are represented within each category
Plants – food or poison
Animals – attack or food
Tools – function, developed later
Organised Unitary Content Hypothesis (OUCH)
amodal semantic (conceptual) representation system
- members of semantic category share attributes (humans breathe, composed of certain type of matter)
- core semantic properties of an object tend to be highly intercorrelated (breathing, being composed of water, etc.)
- category comprises highly correlated concepts because of overlapping features
OUCH assumption 1 - how are concepts represented
Assumption 1:
How concepts are represented within semantic memory
- Members of a semantic category cluster close together in feature space
- Within a category representation occurs within semantic space and is lumpy
OUCH assumption 2 - damage to lumpy regions
Category specific patient deficits due to damage to lumpy region(s) within semantic space
- Brain damage affects category members because it
-> Affects objects/concepts with similar properties and these are stored in adjacent neural areas
OR
-> Affects the highly correlated features of category members
OUCH pred 1, disruption of features representation
- Category impairments would occur due to disruption of feature representations of items within the impaired category, and not others
- Optic aphasia – cannot name an object but patient can mime the use of the object
-> Fits with dissociation between word access to semantics and object access to semantics and the strong link between visual attributes of an object and its use
OUCH pred 2, relative sparing of categorisation performance
OUCH predicts relative sparing of categorisation performance
- Patients with impaired object naming or the inability to name the attributes (features) of an object can still name the object’s superordinate category
OUCH pred 3
OUCH predicts category specific deficits
Category impairments would occur due to disruption of feature representations of items within the impaired category
Problems with OUCH predictions
- OUCH is consistent with patient data showing category specific deficits
- But the type of featural representation not defined
- Ways information clusters together not specified
- Functional rather than neural approach
Conceptual-structure account
Systematic relationship among properties of members of a category e.g., animals, furniture, vehicles
- bird: large, beak, wings, eats fish, flies, etc
-> Relationship between features of concepts which links them together into categories
-> Category specific deficits due to damage to conceptual system
Conceptual-structure account assumption1
- Living things have more shared features than non-living things.
- In other words, non-living things have more distinct/informative features than living things
Conceptual-structure account assumption2
- Living things - biological information is highly correlated with shared perceptual properties (can see - has eyes)
- And for artefacts function information is highly correlated with distinctive perceptual properties (used for spearing - has tines)
Conceptual-structure account assumption3
- Features that are highly correlated with other features will be more resistant to damage than features that are not highly correlated
- OR disrupting access to a given feature will disrupt access to highly correlated features
Conceptual-structure account pred 1A, mild and severe, living v nonliving
Mild brain damage -> deficit for living things
Severe brain damage-> deficit for non-living things
- Moss et al. (1998; 2005;2001) – living things have more shared features while non-living things have more distinct things
- Living things will show impairment at any level of damage, except severe since individual features of animals are less unique and therefore more likely to be damaged
- Artefact impairment only occurs with severe damage as the distinction between form and function is strongly correlated and therefore robust to brain damage
- Category specific deficits based severity of damage
Conceptual-structure account pred 1B, severe and mild, living v nonliving
Severe brain damage -> deficit for living things as whole sets of intercorrelated features are wiped out
Mild brain damage -> deficit for non-living things (artefacts) as these concepts have more informative/distinct features that are wiped out at this level of damage
- Devlin et al., 1998
Evidence to refute conceptual-structure account
- Alzheimer’s patient data – used to develop theories not replicated
- Cannot explain selective deficit narrowly defined categories
-> i.e., defuse brain damage – selective category deficits such as fruits/vegies, body parts - Problem for assumption that the number and degree of intercorrelated properties relevant to all living things
- Degree of severity argument
-> JJ and PS have similar levels of task performance (assume similar degree damage), yet show a double dissociation
Problems with conceptual-structure account
- theories ok with broad category deficits but have problems accounting for fine-grained deficits
- alternative views about degree of brain damage and impairments to living v non-living things, views are in opposition
