language disorders october 12, 2005. types of disorders aphasia: acquired disorder of language due...
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Language Disorders
October 12, 2005
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Types of Disorders
• Aphasia: acquired disorder of language due to brain damage
• Dysarthria: disorder of motor apparatus of speech• Developmental language disturbances• Associated disorders
– Alexia
– Apraxia
– Agraphia
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Major Historical Landmarks
• Broca (1861): Leborgne: loss of speech fluency with good comprehension
• Wernicke (1874): Patient with fluent speech but poor comprehension
• Lichtheim (1885): classic description of aphasic syndromes
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C
M A
Lichtheim’s Model
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Arcuate fasciculus
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Syndrome Symptom Deficit Lesion
Broca’s Aphasia speech production; sparse,
halting speech, missing function words, bound
morphemes
Impaired speech planning and production
Posterior aspects of 3rd frontal convolution
Wernicke’s Aphasia
Auditory comprehension, fluent speech, paraphasia, poor repetion and naming
Impaired representation of sound structure of words
Posterior half of the first temporal gyrus
Pure motor speech disorder
Disturbance of articulation, apraxia of speech,
dysarthria, aphemia
Disturbance of articulation Outflow from motor cortex
Pure Word Deafness
Disturbance of spoken word comprehension, repetition
also impaired
Failure to access spoken words
Input tracks from auditory cortex to Wernicke’s area
Transcortical Motor Aphasia
Disturbed spontaneous speech similar to BA; relatively preserved
repetition, comprehension
Disconnection between conceptual word/sentence representations and motor
speech production
Deep white matter tracks connecting BA to parietal
lobe
Transcortical Sensory Aphasia
Disturbance in single word comprehension with
relatively intact repetition
Disturbed activation of word meanings despite normal recognition of auditorily
presented words
White matter tracks connecting parietal and
temporal lobe
Conduction Aphasia
Disturbance of repetition and spontaneous speech,
phonemic paraphasia
Disconnetion between sound patterns and speech
production mechanisms
Arcuate fasciculus; connection between BA and
WA
Lichtheim’s (1885) Aphasic SyndromesLichtheim’s (1885) Aphasic Syndromes
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Additional Aphasia SyndromesAdditional Aphasia Syndromes
Syndrome Symptom Deficit Lesion
Anomic Aphasia single-word production,
marked for common nouns; repetition and
comprehension intact
Impaired storage or access to lexical entries
Inferior parietal lobe or connections within
perisylvian language areas
Global Aphasia Performance in all language functions
Disruption of all/most language components
Multiple perisylvian language components
Isolation of the language zone
Spontaneous speech, comprehension, some
preservation of repetition; echolalia common
Disconnection between concepts and both
representations of word sounds and speech
production
Cortex outside perisylvian association cortex
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Broca’s Aphasia
• Telegraphic, effortful speech
• Agrammatism
• Some degree of comprehension deficit
• Writing and reading deficits
• Repetition abnormal – drops function words
• Buccofacial apraxia, right hemiparesis
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Wernicke’s Aphasia
• Fluent, nonsensical speech
• Impaired comprehension
• Grammar better preserved than in BA
• Reading impairment often present
• May be aware or unaware of deficit
• Finger agnosia, acalculia, alexia without agraphia
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Conduction Aphasia
• Fluent language
• Naming and repetition impaired
• May be able to correct speech off-line
• Hesitations and word-finding pauses
• May have good reading skills
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Global Aphasia
• Deficits in repetition, naming, fluency and comprehension
• Gradations of severity exist
• May communicate prosodically
• Involve (typically) large lesions
• Outcome poorest; anomic
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Transcortical Aphasias
Transcortical Motor• Good repetition• Impairment in
producing spontaneous speech
• Good comprehension• Poor naming•
Transcortical Sensory• Good repetition• Fluent speech• Impaired
comprehension• Poor naming• Semantic associations
poor
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Associated Deficits
• Alexia without Agraphia– Impairment in reading with spared writing
• Apraxia– Loss of skilled movement not due to weakness
or paralysis
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Fundamental Lessons
• Language processors are localized
• Different language symptoms can be due to an underlying deficit in a single language processor
• Language processors are regionally associated with different parts of the brain in proximity to sensory or motor functions
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What Language Disorders RevealWhat Language Disorders Reveal about Underlying Processes about Underlying Processes
• Pure Word Deafness: selective processing of speech sounds implies a specific speech-relevant phonological processor
• Transcortical Sensory Aphasia: repetition is spared relative to comprehension; selective loss of word meaning; some cases suggest disproportionate loss of one or more categories
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What Language Disorders RevealWhat Language Disorders Reveal about Underlying Processes about Underlying Processes
• Aphasic errors in word production: reveal complex nature of lexical access– Phonological vs. semantic errors: independent vs. interactive
relationship?– Grammatical class: nouns vs. verbs (category specificity)
• Broca’s aphasia: syntax comprehension and production– Central syntactic deficit; loss of grammatic knowledge– Problems in “closed-class” vocabulary (preposition, tense
markers)– Limited capacity account– Mapping account (inability to map from parsing to thematic
roles)
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Aphasia and the Semantic System
• Meaning stored separately from form
• Models of representation in semantics– Feature-based models (see categorization)– Nondecompositional meaning
• Modality-specific semantic deficits: optic aphasia as an example
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Two Models of Semantic Organization
One Semantic System
Multiple Semantic Systems