Semantic Dementia 2 Notes

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

Conclusion

• Object 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...

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