20 Semantic memory

Question 1

What are the 4 types of impairments associated with semantic memory?

Answer 1

• Semantic dementia (SD) - cause by frontal temporal dementia
• Herpes simplex viral enchephalis (HSVE)
• Stroke (left temporal lobe)
• Alzheimers

Question 2

What is HSVE?

Answer 2

Herpes simplex viral enchepalis is a viral infection that effects temporal lobes and the frontal lobes. It occurs both unilaterally and bilaterally.

Patients have category specific semantic memory impairments. e.g. not being able to describe living things apart but can describe non-living things

This could also be modality specific: can tell explain a picture (visual stimuli) but not explain when asked (auditory)

Question 3

What is semantic dementia?

Answer 3

• Progressive, selective loss of semantic knowledge when tested in any modality
• Not category-specificity
• Profound loss of word meanings: evident in comprehension & production (empty speech)
• Inability to recognise objects (agnosia)
• Other cognitive abilities (e.g. episodic memory) and other aspects of language (syntax, phonology, pragmatics) seem to be much better preserved in activities of daily living (although other deficits become evident on testing)
• Characterised by severe degeneration of anterior and lateral temporal lobe, bilateral but often asymmetric (and left > right)

Question 4

What are the theories that explain semantic memory organisation?

Answer 4

• Distributed only view
• Distributed plus-hub view
• Parallel distributed network

Question 5

What is the distributed only model and how does it explain semantic memory deficits?

Answer 5

It contains nodes that connect to one another.
It explains category and modal specific deficits - as connections are lost, part of the network are lost and so categories get hindered.
This doesn’t explain semantic dementia though, which has semantic deficits across categories and modalities

Question 6

What is the distributed-plus-hub view?

Answer 6

It builds on the distributed-only view model by adding a hub that connects all the nodes - “a representation that is independent to the task”

This assists in understanding semantic dementia, as damage to this hub produces deficits in all modalities and categories.

Question 7

How does the parallel distributed processing fit in with all this?

Question 8

Describe the work of Ralph & Rogers (2007) regarding semantic memory impairments in individuals with HSVE compared to individuals with SD

Answer 8

• conducted a battery of tests: 7 HSVE, 8 SD
• matched individuals with the severity of semantic memory impairment on a word matching taks (e.g. given dog -> had to match with picture of dog)
• SD had far worse memory recall but was not category specific
• HSVE had categorical impairments
• semantic error was much higher in HSVE whilse general errors were seen more in SD

They proposed a netword