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A Neurolinguistic Introduction to Aphasia

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    A Neurolinguistic Introduction

    to Aphasia

    Cognitive Sciences

    2006

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    Outline

    Aphasia and language

    Double dissociations

    Localization of (linguistic) function Broca, Wernicke, and the syndrome

    approach to aphasia

    Behavioral studies of aphasia Neuroimaging studies of aphasia

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    Patient B: "Well it's a it's a place and it's a g-girl and a boy . . . and the-they've got

    obviously something which is made made made well it's just beginning to go and

    be rather unpleasant ha! ha! And this is in the this is the the woman and she's

    putting some stuff and the it's it's that's being really too big to do and nobody

    seems to have got anything there at all and it's . . . I'm rather surprised that butthere you are this this stuff this is coming they were both being one and another

    put here and um I suppose the idea is that the two people should be fairly good

    but I think it's going somewhere and as I say it's down again . . . let's see what

    else has gone the this is just I don't know how she how they did this but it must

    have been fairly hard when they did it and I think there isn't very much there I

    think."

    Patient A: (Points to the water andlaughs) "Ah . . . ah . . . girl and boy,

    ah oh er er dear . . . girl (points to

    the woman) cof (points to the cloth)

    and, er oh er dear me . . . er (points

    to the stool) er steps um window,

    curtains . . . a pot and an er (pointsto the water) oh dear me . . . OK"

    Aphasic language production

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    Defining aphasia

    Rao 1994

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    Defining language

    Speech?

    Communication?

    Thought? A separate system of knowledge?

    Double dissociations

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    Double dissociations

    Cognitive systems dissociate from one another One can be impaired while another is (relatively) spared

    This is taken as evidence that cognitive systems are likelydistinct from one another the brain/mind is MODULAR inits organization

    Language is not a monolith

    Dissociations require caution:

    - maybe one function is just more vulnerable to certainkinds of damage than another

    - one task might be more difficult than another

    - Apparent dissociations might arise from non-modularsystems

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    Single word reading by two alexic patients: Warrington 1981, Patterson 1979, Plaut & Shallice 1993

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    Localization of function

    Phrenology Gall, Spurzheim, early1800s

    Different cognitive functions can be

    localized to different parts of the brain

    Level of development of a particularfunction is reflected in skull formation

    The sad tale of Phineas Gage Dissociation of language from other

    cognitive faculties

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    Localization of language

    Paul Broca (1861): patientTan

    Slow, effortful, nonfluent

    speech with many omissions;

    but good comprehension

    on parle avec lhemisphere

    gauche

    Carl Wernicke: patientswith posterior lesions in

    the left hemisphere

    comprehension is

    impaired but speech isfluent

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    From the Whole Brain Atlas at Harvard Medical School :

    http://www.med.harvard.edu./AANLIB/home.html

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    Wernickes prediction

    Predicted two languagecenters:

    Brocas area: speech

    articulation

    Wernickes area: speechcomprehension

    Predicted a third

    disconnection syndrome

    damage to the arcuatefasciculus

    Conduction aphasia

    Chris Rorden, University of Nottinghamhttp://www.psychology.nottingham.ac.uk/staff/cr1/c83lnp/c83lnp2.pdf

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    Wernicke-Lichtheim model

    Wernickes areaBrocas area

    Concepts (distributed)

    arcuate

    fasciculus

    Brocas aphasia Wernickes aphasia

    conduction

    aphasia

    Conduction aphasia: can produce and understand meaningful speech, but cannot

    repeat words they hear

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    Classifying the aphasias

    Advantages of classifying patients into syndromes increases interscientist communication

    groups homogeneous patients for research and for therapy

    describes a set of behaviors for diagnostic purposes

    can help in determining a prognosis

    contribute data toward localization of lesion - advancing ourunderstanding of the relations between brain and mind

    Disadvantages of syndrome approaches limits thought

    exceptions may be more interesting and more fruitful for research may force a label onto a patient who does not really fall into a

    particular syndrome category

    presumes too much about premorbid functioning

    localization issues may be vexed by individual differences

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    U d t di ti

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    Understanding agrammatism: a

    central syntactic deficit? Caramazza and Zurif 1976: agrammatics do have a comprehension

    deficit, and it parallels their production disabilities The test case: Semantically reversible sentences

    Theta-roles: assignment of interpretive roles to syntactic objects

    subject verb object Grammatical roles

    John kissed MaryTheta roles

    Non-canonical word order reliance on grammatical structure

    object verb subject

    John was kissed by Mary

    central disruption of the syntactic parsing component of thelanguage system Berndt & Caramazza 1980

    Agent Patient

    Agent?? Patient??

    U d t di ti

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    Understanding agrammatism: a

    mapping deficit?

    Problems with the central syntactic deficit account: agrammatics do have some ability to interpret complex

    utterances - in particular, they are quite good at

    grammaticality judgment Some agrammatics are modality-specifically impaired

    note assumptions of central deficit hypothesis

    Some fluent aphasics show comprehension deficitssimilar to those found in Brocas aphasics

    Perhaps the deficit is not central to syntax, butinvolves the transfer from syntactic structure tosemantic structure of a sentence: a mapping deficit

    (Saffran et al 1980)

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    Understanding agrammatism: the

    trace deletion hypothesis We have seen that things move around in sentences

    And we have seen that interpreting sentences does notjust mean knowing where the subject and the object are it means knowing what theta roles to assign, too

    In the normal language system, movement leavestracesbehind

    Theta rolescan be assigned to traces, and thent ransmit tedto the moved item

    Grodzinsky (1990) asked: what if traces get deletedfrom the syntactic representation?

    Maybe this is what happens in agrammatism

    The trace deletion hypothesis

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    Trace Deletion Hypothesis Assigning a theta role to the girl

    should be no problem no trace

    involved in that P by assigns a theta role of Agent

    so the girl = Agent

    But, if traces are deleted, then the

    boy has no theta role So follow your instinctsUSUALLY, the first noun in asentence is the Agent

    So the boy is probably an Agent

    Now, the agrammatic thinks:the boy = Agent AND

    the girl = Agent

    What to do? Guess at the right

    interpretation of this sentence

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    Neuroimaging and aphasia

    Price & Crinion 2005

    f

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    Right hemisphere compensation after

    aphasia

    Semantic processing of visually presented words: Gold &Kertesz 2000

    Patient GP with a large left hemisphere lesion, andprofound global aphasia, including extreme impairmentof auditory-verbal comprehension, speech and writing

    GP demonstrated considerable ability for semanticprocessing of visual words

    identified superordinate and subordinate visual wordsaccurately

    could distinguish proper written names from frequentnouns matched for initial letter and length

    could distinguish printed words representing living thingsfrom nonliving things

    performed well on the Pyramids and Palm Trees Test

    (Howard & Patterson,1992)

    Ri h h i h i f

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    Tasks: Shoe

    Sock Hat

    Semantic - Which of the lower words is more closely related to the top

    one? (Response: L/R)

    Ortho

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