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Aphasia

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Take a look at several language processes that ... Examine neuropsychological data which bear on theories about the nature and ... (3) Anomic or amnesia aphasia ... – PowerPoint PPT presentation

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Title: Aphasia


1
Aphasia
  • What is aphasia?
  • Types of aphasia
  • Cognitive neuropsychology and aphasia
  • Syndrome or symptoms?
  • Computational cognitive neuropsychology

2
The forthcoming lectures
  • Take a look at several language processes that
    have interested neuropsychologists (e.g.,
    listening, speaking, reading and writing).
  • Examine neuropsychological data which bear on
    theories about the nature and operation of these
    language processes.
  • Emphasis is on cognitive neuropsychology as a
    research discipline, but practical/clinical
    applications will also be illustrated.
  • Introduce computational neuropsychology.

3
What kind of language operations?
  • Modular Interactive
  • mandatory, encapsulated non-mandatory
  • domain specific non domain specific
  • Rule based Associative
  • explicit grammatical rules pattern of connections
  • operating on linguistic units operating among
    units
  • symbolic units non symbolic units

4
What kind of representations?
  • Semantically transparent Distributed
  • linguistic representations neuron like units with
  • phonemes, syllables, words no immediate referent
  • Discrete Continuous
  • binary (all or none) activation level
  • words as units words as patterns
  • damage causes total loss partial loss of function

5
What is Aphasia?
  • Aphasia is a neurological disorder caused by
    damage to those areas of the brain that are
    responsible for language (frontal/temporal).
  • Primary signs of the disorder include difficulty
    in expressing oneself when speaking, trouble
    understanding speech and difficulty with reading
    and writing.
  • Aphasia is most commonly seen in adults who have
    suffered a stroke but aphasia can also result
    from a brain tumor, infection, head injury, or a
    dementia that damages the brain.

6
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7
Types of aphasia
  • Aphasia can be divided into four categories
  • (1) Expressive aphasia
  • conveying thoughts through speech or writing.
  • (2) Receptive aphasia
  • understanding spoken or written language.
  • (3) Anomic or amnesia aphasia
  • difficulty using the correct names for objects,
    people, places, or events.
  • (4) Global aphasia
  • loss of all comprehension and expression.

8
Differential diagnosis
  • There are two critical features of the language
    produced by aphasic patients
  • Fluent/Non-fluent does language production
    require great effort are there many pauses and
    ums and ers and is the number of words
    produced per unit of time very low?
  • Grammatical/Agrammatical does language
    production lack grammatical structure is it
    mostly just a string of nouns (note, though, that
    the nouns themselves can be the correct ones).

9
Brocas aphasia
  • Speech is non-fluent, slow and laboured.
  • Grammatical structure is absent.
  • Comprehension of morphemes is normal.

10
Speech sample
  • Doctor Why did you come to hospital?
  • Patient AhMondayah Dad and Pauland
    Dadhospital. Twoahdoctorsand thirty
    minutesand yesahhospital. Wednesdaynine
    oclockdoctors. Two doctorsand ahteeth.
    Yeahfine.

11
Wernickes aphasia
  • Speech is fluent, but full of neologisms.
  • Grammatical structure is preserved.
  • Comprehension of morphemes is impaired.

12
Speech sample
  • Doctor Why did you come to hospital?
  • Patient Never, now mista I wanna tell you this
    happened when happened when he rent. His - kell
    come down here and is - he got ren something. And
    he roden all these arranjen from the pedis on
    from iss pescid.

13
What is the prognosis?
  • The outcome of aphasia is difficult to predict
    given the wide range of variability of the
    condition but some skills are easier to treat.
  • Generally, people who are younger or have less
    extensive brain damage fare better.
  • The location of the injury is also important and
    is another clue to prognosis.
  • In general, patients tend to recover skills in
    language comprehension more completely than those
    skills involving expression.

14
Cognitive neuropsychology
  • Cognitive psychologists study the behaviour of
    people with normally functioning mental systems
    to draw conclusions about the mind.
  • Cognitive neuropsychologists specialise in the
    study of behaviour of individuals whose language
    processes are not functioning normally (e.g.
    after a stroke or head injury).
  • They use data from studies of people with
    language impairments sustained after brain damage
    - aphasia - to test, extend or develop theories
    about normal language processing.

15
Six assumptions of cognitive neuropsychology
  • Brain injured patients show dissociations of
    language function that are informative.
  • We can make inferences about the functional
    architecture of normal language processing by
    studying these dissociations.
  • Double dissociations provide strong evidence for
    independent language processes.
  • The primacy of single case studies.
  • "Modularity of mind (Fodor).
  • Associations of language impairments are not
    useful for cognitive neuropsychology.

16
Problems with associations
  • Traditional clinical neuropsychology is based on
    associations rather than dissociations.
  • Co-occurence of symptoms is used to group
    patients into syndromes e.g. Brocas aphasia.
  • However, symptoms often co-occur for purely
    anatomical rather than functional reasons.
  • Even the study of relatively robust aphasic
    syndromes has not told us anything about the
    nature of language processing nor the role of
    specific brain regions for language tasks (though
    see Robinson et al 1999 for BA45).

17
Gerstmanns syndrome
  • A pattern of co-occurring symptoms that result
    from a specific lesion in the angular gyrus
    (which is in the left parietal lobe).
  • finger agnosia
  • left-right confusion
  • agraphia
  • acalculia
  • Associations are OK for localisation of brain
    lesions but are not useful for understanding the
    organisation of language processes and are not
    necessary for lesion location (fMRI).

18
Aphasia and cognitive neuropsychology
  • The syndromes of aphasia tell us little about the
    nature of language processing beyond the fact
    that receptive and expressive language skills are
    dissociable and that grammar and meaning are
    processed independently in the human mind.
  • The study of language breakdown can be used to
    develop and to test theories of cognitive
    processing - this will be the focus of the
    lectures.
  • Theories can be used to design connectionist or
    computational models and brain imaging studies in
    order to understand brain-behaviour.

19
Computational psychology
  • This is an approach to cognitive psychology in
    which models of processing in some cognitive
    domain such as language (or memory, object
    recognition or perception) are translated into
    explicit computer programs.
  • These programs process input in exactly the same
    way that people do or so the modeler assumes
    (e.g. Plaut Shallice, 1993).
  • Models that are expressed as computer programs
    are called computational models.

20
Why do computer modeling?
  • Not because we assume the brain or the mind is a
    computer but for two scientific reasons
  • If you turn a theory into a computer program then
    you discover many parts of the theory need
    further specification this forces the theorist
    to make the theory complete (Plaut et al., 1996).
  • Once there is a complete theory and a program
    that represents it you can test the theory more
    rigorously because the program can be used to
    explore how variables and experimental
    manipulations influence the model.

21
Computational cognitive neuropsychology
  • Computational models can be used to test theories
    like data from normal subjects, brain imaging
    studies and brain damaged patients.
  • Computational models can be lesioned to test them
    against the performance of patients who are
    thought to have a specific cognitive deficit.
  • If the intact program behaves in the same way as
    human subjects do and the lesions of the program
    behave like patients then the theory that
    generated the program will look feasible.

22
Summary
  • Studies of aphasia have enabled us to develop
    theories of normal language processing and to
    identify the necessary cognitive processes.
  • Studies of aphasic patients have shown that the
    syndrome approach to neuropsychology is limited
    in what it can tell us about brain-behaviour
    relationships.
  • Computational cognitive neuropsychology aims to
    understand the behaviour of aphasic patients by
    lesioning connectionist models of language.

23
References
  • Plaut, D., Shallice, T. (1993). Deep dyslexia
    A case study of connectionist neuropsychology.
    Cognitive Neuropsychology, 10(5), 377-500.
  • Plaut, D.C., et al. (1996). Understanding normal
    and impaired word reading Computational
    principles in quasi-regular domains.
    Psychological Review, 103(1), 56-115.
  • Kay, J. et al. (1993). The Psycholinguistic
    Assessment of Aphasia (PALPA). LEA. Hove.
  • Robinson, G. et al. (1998). Dynamic aphasia an
    inability to select. Brain, 121, 77-89.

24
Glossary
  • Abstract words refer to concepts (love peace).
  • Concrete words refer to physical nouns (cat).
  • Content words Nouns, verbs adjectives open (new
    words can be added).
  • Function words articles, prepositions,
    conjunctions closed class.
  • Mental lexicon store of information about words.
  • Morpheme smallest unit of language that has
    meaning.
  • Orthography visual characteristics of a word.
  • Phonemes smallest unit of sound.
  • Pragmatics context dependent meanings of words.
  • Prosody changes in intonation giving meaning.
  • Semantics the meaning of a word.
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