Week 9 Lecture 9 - the speaking brain 2 Flashcards
Where does much of what we know about language in the brain come from?
- lesion studies –> often post-stroke
What is the hub-and-spoke model?
Amodal ‘hub’:
* Representation of specific concepts irrespective of modality
* Categorisation of exceptional concepts
* Generalisation to form categories despite high conceptual feature variability
Distributed, grounded ‘spokes’:
* Semantic representations grounded in
sensory and bodily areas (‘spokes’)
* E.g., representations of the word ‘robin’ or the sound of a robin’s bird call, or the
colours of a robin
What does the hub-and-spoke model predict?
if there is an amodal hub then focal damage to that region would lead to a global semantic impairment independent of modality of information
- E.g., struggling to identify a picture of a robin when given either its name (word), colours, sound etc.
What is semantic dementia (SD)?
Global semantic impairment which:
* Is cross-modal
* Shows strong typicality effects
* Shows preservation of general relative to specific information
Relative sparing of other language and cognitive abilities
What evidence is there for a hierarchy of representations in the brain?
- Rogers et al., (2006) fMRI study
- fMRI study of naming and categorisation
- Processing at specific level activates anterior temporal pole
Global semantic impairment - Patterson et al., (2007)
Task:
* Presented with a category label (e.g.,
“animal”, “dog”, “beagle”), then a colour
photograph.
* Indicate whether the label matches the
photo.
What was the outcome?
SD worse at correctly matching specific
category labels (“beagle”)
Global semantic impairment - Patterson et al., (2007)
Task:
* Verbal picture naming responses from one SD patient over time
What was the outcome?
SD gradually lose specific concepts and rely on superordinate category labels
Global semantic impairment - Patterson et al., (2007)
Task 1:
* Presented with a 2 drawings of an
object in different colours
* Indicate which version is coloured
correctly
Task 2:
* Presented with a drawing of an animal
with typical or atypical features
* Indicate which drawing is accurate to a
real animal
What was the outcome?
SD are worse at correctly identifying features if they are atypical for the category (orange vegetable, larger eared animal)
Global semantic impairment - Patterson et al., (2007)
Task:
* Presented with a line drawing of an animal,
which is then covered
* After a 10s delay, draw the animal from memory
What was the outcome?
Atypical features for ‘animals’ (e.g., hump or flippers) are omitted
* Typical features for ‘animals’ (e.g., having 4 limbs or a tail) are added
What is the summary of evidence from SD for global sematic impairment?
Some part(s) of the brain is responsible for specific semantic concepts, regardless of whether the task is to recognise the
category, name, draw, or identify feature
According to a fully grounded model, the global deficits in SD could be caused by what?
uniform but distributed damage to all the modality-specific, perceptual and motor areas where representations of these objects are grounded
According to the hub and spoke model, the global deficits in SD could be caused by what?
damage to just the amodal hub, thus affecting generalisation across categories and representation of atypical exemplars,
regardless of task
What brain areas are affected in SD?
Convergent evidence from different imaging modalities shows (bilateral) damage to anterior temporal lobe
If the global deficit in SD is caused by damage to a circumscribed brain region (anterior temporal lobes), can the global deficit be explained any other way?
Semantic dementia vs.:
* AD – semantic impairment due to spread of pathology
* HSVE – semantic impairment caused by viral infection
* Transcortical sensory aphasia – semantic impairment caused by stroke
What patient evidence is there for the anterior temporal lobe as an amodal hub?
- Alzheimer’s disease vs Semantic Dementia
- Herpes Simplex Viral Encephalitis (HSVE) vs SD
- Transcortical Sensory Aphasia (TSA) caused by stroke
What is HSVE?
- HSVE is the most common viral encephalitis in humans
- damage is usually widespread
- characterized by dense anterograde amnesia, and sometimes by impairments of semantic memory and/or executive functions
- BUT: when semantic deficits are present, damage is focus in the anterior temporal lobes
What are the effects of cumulative cueing on TSA and SD (evidence for the ATL as amodal hub: patient evidence)?
- TSA: a deficit of access to semantic representations
- SD: a deficit due to degradation of semantic representations themselves
What is syntax?
the rules that specify how words can be combined into sentences
What is parsing?
assigning a syntactic structure to words
True or false?
Speech without syntax is difficult to understand
True
Demonstrate how there is a history of localising cognitive functions to brain areas
- Paul Broca (1861) – localised ‘speech production’ to a dedicated ‘language centre’ (via autopsy), termed ‘Broca’s area’
What is Broca’s aphasia cardinal symptom?
cardinal symptom is agrammatism (loss of grammar) in speech production: speech which is characterised by the absence of function words and verbs
What is Broca’s aphasia often assessed through?
the Cookie Theft test
True or false?
Broca’s aphasia involves only deficits in speech production
False
Broca’s aphasia involves deficits in both
production and comprehension of syntactically complex sentences
When does Broca’s area show greater activity?
Broca’s area shows greater activity with increasing syntactic complexity in fMRI
What is the current view of the subdivisions of Broca’s area?
BA44: processing hierarchical structures and sequencing
* E.g., sentence-level constructions
* Feedforward predictions
BA45: working memory and semantic control
* E.g., judging semantic-ness, such as concreteness or synonym judgements
What evidence disputes the current view of the subdivisions of Broca’s area?
Posterior temporal lobe structures also active for syntactic vs. semantic processing
Parsing: assigning syntactic structure to words
What is the debate around this?
Debate as to whether this is:
* Structure-driven (syntax separate from semantics) –> garden path sentences
* Discourse-driven (semantics influences syntax processing) –> High or Low congruence semantic context biases processing of homophones
Concerning syntax and semantics, what do the N400 and P600 ERP components show?
N400 ERP component:
* Semantic anomalies regardless of sentence context
* “I take coffee with milk and dog”
* “river-bank-money”
- P600 ERP component:
- Syntactic anomalies regardless of semantic content
- “The boiled watering can smokes the telephone in the cat
What is lexicalisation?
the selection of a word based on the
meaning that one wishes to convey
What is Lexeme?
the phonological code that drives articulation
What is Lemma?
- a modality-independent word-level entry that specifies the syntactic components of the word
- Syntax is independent of modality of production (e.g., speaking, writing)
What is Logopenic progressive aphasia?
- disorder of word retrieval
- Often associated with Alzheimer’s disease pathology
- Speech characterised by word-finding pauses
- Impaired speech processing (repetition or comprehension) for sentences more than words
- Impaired phonological working memory
- Atrophy in left posterior temporal cortex
What is Levelt’s model of word retrieval?
Discrete, sequential stages
Can explain:
- ‘tip-of-the-tongue’ phenomenon
- Activation of lemma without lexeme
- Correctly selecting a word based on its syntactic properties, when it has a homophone with the same phonological properties:
* ‘watch’ (accessory/to watch)
* “I have watched that show”
* Not “I have a watch that show”
What is the SLAM model of word retrieval?
SLAM: semantic -> lexical -> auditory -> motor
- Speech production involves ventral stream in reverse (temporal lobes
to auditory cortex) followed by dorsal stream (auditory to frontal)
- The auditory stage acts as a forward model (predicts the sensory
consequences of motor actions)
What patient evidence is there for the SLAM model?
Fridriksson et al. (2018)
* Lesion-symptom mapping of damage to grey and white matter in stroke patients
* Performance on variety of language tasks
* To test the dual steam model of language production and comprehension
What is an example of an error in word level representations? (word retrieval errors)
Freudian slip: the substitution of one word for another that is sometimes thought to reflect the hidden intentions of the speaker
What is an example of an error in phonemelevel representations? (word retrieval errors)
Malapropisms, e.g., spoonerism
- A speech error in which initial consonants are swapped between words
In articulation, what is syllabification?
- the process of segmenting phonological information into syllables across adjacent morphemes and adjacent words
- Syllables can occur across morphemes (written words)
- “He owns it” = “he own zit”
- Neural correlates:
- Phoneme-level: basal ganglia
- Syllable-level: ventral premotor
Give 2 examples of disorders of articulation
- apraxia of speech
- dysarthria
What is apraxia of speech?
- Damage to the insula
- Difficulty shaping the vocal tract
Altered speech production despite intact:
* Semantics, syntax
* Word retrieval
* Muscle tone of articulators
What is dysarthria?
- Damage to the cerebellum and basal ganglia
- Impairment in muscular contractions of articulators
Altered speech production despite intact:
* Semantics, syntax
* Word retrieval
