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Language and Cognition Colombo, June 2011. Day 5 Aphasia Dissociations. Defining aphasia. Rao 1994. Defining language. Speech? Communication? Thought? A separate system of knowledge? Double dissociations. Double dissociations. Cognitive systems dissociate from one another
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Language and CognitionColombo, June 2011 Day 5 Aphasia Dissociations
Defining aphasia Rao 1994
Defining language • Speech? • Communication? • Thought? • A separate system of knowledge? • Double dissociations
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 distinct – the brain / mind is MODULAR in its organization • There are dissociations within language too
Localization of function • Phrenology – Gall, Spurzheim, early 1800s • Different cognitive functions can be localized to different parts of the brain • Level of development of a particular function is reflected in skull formation • The sad tale of Phineas Gage • Dissociation of language from other cognitive faculties
Paul Broca (1861): patient ‘Tan’ Slow, effortful, nonfluent speech with many omissions; but good comprehension on parle avec l’hemisphere gauche Carl Wernicke: patients with posterior lesions in the left hemisphere comprehension is impaired but speech is fluent Localization of language
Predicted two language centers: Broca’s area: speech articulation Wernicke’s area: speech comprehension Predicted a third ‘disconnection’ syndrome – damage to the arcuate fasciculus “Conduction aphasia” Wernicke’s prediction Chris Rorden, University of Nottingham http://www.psychology.nottingham.ac.uk/staff/cr1/c83lnp/c83lnp2.pdf
Wernicke-Lichtheim model Concepts (distributed) Wernicke’s aphasia Broca’s aphasia Wernicke’s area Broca’s area arcuate fasciculus conduction aphasia Conduction aphasia: can produce and understand meaningful speech, but cannot repeat words they hear
Wernicke-Lichtheim model • Broca’s aphasia • Wernicke’s aphasia • Conduction aphasia • Transcortical motor aphasia • Dyspraxia • Transcortical sensory aphasia • Pure word deafness
Boston classification • Nonfluent aphasias • Broca’s aphasia • Transcortical motor aphasia • Global aphasia • Fluent aphasias • Wernicke’s aphasia • Conduction aphasia • Anomic aphasia • Alexia / Agraphia • Some rare syndromes: pure word deafness, optic aphasia • Boston Diagnostic Aphasia Exam (Goodglass, Kaplan & Barresi, 2001)
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 our understanding 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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