This is an extract of our Semantic Dementia 2 document, which we sell as part of our Neuropsychology of Memory Notes collection written by the top tier of Durham University students.
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Semantic Dementia (2) It is often claimed that SD patients have spared object use for objects they cannot recognise using other tests - may not be able to describe what the object does but when asked to use it - they use it correctly ? is action use (actions semantics) relatively spared?
If actions can be selectively spared ? can they also be selectively impaired? - is there really dissociation Apraxia ? disorder of skilled movement - inability to execute learned purposeful movements - despite having the desire + physical capacity to perform the movements - not caused by a loss of sensory capacity , abnormality of tone or posture, intellectual deterioration or poor comprehension ----- Steinthal (1871) - coined the term
Liepmann (1900): first analysis of apraxia - focused on one of 3 varieties - "ideational" ? patient incapable of making appropriate use of objects upon command????
Patient diagnosed with dementia - he used objects oddly
- Could not perform gestures or demonstrate use of objects to command
- Could make spontaneous hand movements => so not paralysed
- Capable of motor execution of the action => e.g. copying someone else do the action
- Comprehension of instructions was intact Liepmann suggested L hem localisation of "motor memories" He also suggested a disconnection of "sensory memories" ?
understanding instructions + "motor memories" ? allowing action Suggested that apraxia is to do with an inability to utilise "motor memories" - action semantics ?
E.g. Critchley (1966) - woman with biparietal lesion - worked for yrs fishmonger - with development of her symptoms she had difficulties carrying her her job - she didn't know what to do with her knife
- In her mind she knew the steps needed to fillet a fish - however couldn't execute the Apraxia associated with L hem parietal or frontal lesions ? semantic dementia = temporal pole atrophy Possible double dissociation between this + semantic dementia
How could is the evidence for a double dissociation between object semantics + action semantics?
In semantic dementia some instances of what appears to be spared actions semantics:
? Spared action often with highly familiar objects in the home context
This may break down if the context doesn't cue the specific action e.g. stayed in a hotel instead of home - didn't know what the hairdryer did (lack of activation of scripts)
? Spared actions may be triggered by partial semantic knowledge - e.g. confusing a boot with a sock - looks like semantics still intact - lack of specificity
? Spared actions may be triggered by "affordances of the object" - the way in which it is designed may provide clues as to how it is used - e.g. hairdryer pick up by handle - looks like they know how to use it
? Need to control object use in a controlled manner - to determine if it really is spared Semantic Dementia & Object Use Silveri & Ciccarelli (2009) ? explore the role of semantic knowledge in object use??????Analysed performance of patients + controls in object naming, pantomime execution (what would you do with this object without touching it) +
object use Comparisons between patients who had semantic deficits of different severity ? ability to use objects was largely preserved when the deficit was mild - but progressively decayed as the deficit became more severe Naming was generally more impaired than object use Most SD patients were better at using the object than pantomiming use to visually presented object - may be due to affordances or scripts ? only severe cases impaired at using object About a third of object use errors were semantically related (e.g. paint brush for shaving brush) About half were unrelated but recognisable errors e.g. pipe used as a hammer Data shows that there is a sig relationship between severity of the semantic deficit + an inability to use objects For conventional use of objects - semantic knowledge about the object is crucial =>only semantic knowledge - principally knowledge of functional aspects (how the object must be used) can allow using an object in a way that cannot be elicited by its structural characteristics There is also a significant consistency between object knowledge + object use Introduced another task - performance of patients + controls in recognition of object use , pantomime recognition + action recognition - watched other people do it Recognition of object use was impaired in patients with semantic disoders
+ was related to the patients ability to use the object Results indicate that a specific component of semantic knowledge is impaired ? knowledge about function Pantomime recognition + action recognition were also pathological - not only motor tasks involving manipulation of objects or pantomiming were impaired - but also those in recognising the action
This observation seems to support the hyp that the same processes mediate both production of actions + recognition of actions +
manipulable objects No good evidence for dissociable action semantics ConclusionObject use may be relatively spared in the early stages of semantic dementia
- This may be because some intact semantic knowledge is sufficient to cue appropriate action even when it is not specific enough to access full identifying info
- In some cases knowledge of action sequences (schema) may be intact even when produced to inappropriate objects e.g. skilled seamstress sewed holes in socks instead of darning them + the fish filiter - intact knowledge of what to do but can't executed (Critchley et al, 1966)
- In severe cases both action schema + object knowledge are both lost
? No good evidence for dissociation between object semantics + action semantics Relationship between EM + SM
? Know that some patients can have EM impairments with little or no apparent semantic memory impairments
- But semantic memory may not proceed normally in amnesics
? In SD semantic memory impairments are much worse than EM impairments - however ? patients may perform badly in formal verbal tests e.g. story recall
? If SD patients don't understand the semantic context or the meaning of the objects present, this could appear as an EM deficit
? Bransford & Johnson (1972)
- Gave subjects a piece of text - asked to comprehend + recall this
- Either given no contextual details, context after text, partial context before text or context before text
- Increased comprehension + recall scores obtained when ptp presented with appropriate info before the test passages
- Supplying ptp with contextual info after txt produced lower comprehension + recall
? The picture allows you to develop a conceptual understanding of the txt - semantic knowledge
? The context supplies useful schema which aids recall
? When asked to recall a memory episodic like in form - was difficult to recall without relevant - conceptual semantic information being provided Hodges & Graham (2001)?
Initial clinical descriptions of patients with SD suggested that this syndrome provided compelling evidence for a dissociation between preserved autobiographical + impaired semantic memory Patients are typically well-orientated + can relate the details + incidents about their life
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