LCS 11: Cognitive Science - Claremont Colleges
Transcript of LCS 11: Cognitive Science - Claremont Colleges
Pomona College
LCS 11: Cognitive ScienceReading and the brain
Jesse A. Harris
April 15, 2013
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Agenda
Upcoming talks Presentations
Aim to get data by end of this week Meetings next week Group presentations May 1, 6 & 8
Aphasia Broca Wernicke
Alexia Eye movement basics The brain’s letterbox
Writing response # 4, due Friday April 19
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Lorraine TylerThe Neurobiology of Language: Syntax and Semantics
Despite 150 years of study, the properties of the neural languagesystem remain unclear. I will discuss studies involving behaviouraland neuroimaging data on spoken language comprehension.Combining these types of data from healthy people withcomparable data from chronic stroke patients with left hemispherelesions, provides the key ingredients for determining the essentialneural networks in- volved in the syntactic and semantic analysis ofspoken language.
Thursday at 4:15PM, Edmunds 101
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William Marslen-WilsonCross-linguistic Contrasts in Morphological Systems: Neurobiological Perspectives
Current research on the neurobiological foundations of humanlanguage suggests that it is mediated by a coalition of twooverlapping systems. A distributed bihemispheric system, largelyshared with our primate relatives, provides a social andinterpretative framework for language comprehension, as well asbasic mechanisms for mapping sounds onto lexical meanings. Aspecialized left hemisphere system, possibly unique to humans,supports core combinatorial functions underpinning morphosyntax.In recent neuroimaging research in English, Polish, and Arabic weinvestigated how diUerent types of morphological process (broadlydeVned as inWectional and derivational) interface with these twosystems, and whether this diUers across languages.
Friday, April 19: 12 noon, Lunch provided, Edmunds 101
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Aphasia
AphasiaLanguage disorder produced by braindamage
Damage to speciVc areas associatedwith speciVc types of deVcit.
1. Broca’s (production)
2. Wernicke’s (receptive)
3. Conductive
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Broca’s aphasia (1861)
I Leborgne (age 21; single wordword ‘Tam’) and Lelong (age 86;5 words)
I Major speech productiondiXculty
I Other cognitive functions sparedI At autopsy, found lesion in left
frontal lobe
Paul Broca(1824–1880)
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Broca’s aphasia
Example of a Broca’s aphasic:http://www.youtube.com/watch?v=f2IiMEbMnPM
Consider watching this clip at home:http://www.youtube.com/watch?v=NUTpel04Nkc
What do you notice about the patient’s speech?
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Broca’s aphasia
I Speech is slow and laboredI Utterance are not complexI Almost no “function words” like to, for, the, etc.I Yet, words appear to be meaningful and on-topicI In addition, awareness of deVcit
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Wernicke’s aphasia (1875)
I Another type of aphasia, termed“sensory aphasia”
I No signs of speech productiondiXculty
I Lack of comprehension, both inthe utterance produced andreception of speech.
I At autopsy, found lesion in leftposterior temporal gyrus.
Carl Wernicke(1848–1905)
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Wernicke’s aphasia
Wernicke’s aphasia productionhttp://www.youtube.com/watch?v=aVhYN7NTIKU
Wernicke’s aphasia comprehensionhttp://www.youtube.com/watch?v=dKTdMV6cOZw
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Lesion sites
I Broca’s area: left temporal lobe, anterior to primary motorcortex
I Wernicke’s area: Posterior portion of Vrst temporal gyrus
Recap
DeVcit Remainingcapacity
Lesion site
Broca Production,agrammatism
Comprehension,awareness
Frontal lobe
Wernicke Comprehension,Sensicality,Awareness
Speech Wuent Posteriortemporalgyrus
Table: Comparison of aphasia types
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Conduction aphasia
I Very rare type of aphasiaI Damage to the arcuate
fasciculus, a neural pathwaythought to connect Wernicke’sarea and Broca’s area (disputed)
I Both comprehension andproduction seem relativelyspared
I DiXculty repeating speechI Make speech errors and try to
correct them, usually with muchdiXculty
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Experiments on aphasic patients
Non-reversible sentencesCan utilize our world and semantic knowledge to infer thelikely relations between words.
(3) The book that the girl is reading is yellow
Reversible sentencesRelations between words cannot be determined without helpfrom the syntax.
(4) The horse that the bear is kicking is brown
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Experiments on aphasic patientsPredictions
Broca’s If Broca’s aphasics only have a production deVcit forsyntactic processing, they should be able tounderstand complex sentences (just not producethem). Thus, they should be able to perform well onboth reversible and non-reversible sentences.
Wernicke’s Predicted to have across the board diXculty, due toglobal deVcit in comprehension.
Non-reversible Reversible
Wernicke Chance ChanceBroca Good Good
Table: Expectations across diUerent aphasic groups
Experiments on aphasic patients
I Caramazza and Zurif 1976 tested three diUerent kinds ofaphasics, as well as a control
I Presented subjects with reversible and non-reversiblesentences
I From two pictures, asked to pick the appropriatedepiction of the sentence
Non-reversible Reversible
Wernicke Chance ChanceBroca Good Chance
Table: Performance across diUerent aphasic groups
Experiments on aphasic patients
I Evidence that all comprehension capacity for Broca’saphasics is not spared.
I How might we make sense of this pattern? What mightaphasics be doing to process the comprehendnon-reversible sentences that would fail when attemptingto process reversible sentences?
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Geschwind’s 1965 model of language processing
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Reading
Reading processes involves by various factors, including
1. Acuity limitations on the eye
2. Rapid movements to overcome such limitations
3. Decoding of orthographic forms into phonetic ones
4. Access meaning and integration into sentential anddiscourse context
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The eye
RetinaNeural sheet at back ofeye consisting ofphotoreceptors invarious densities.
FoveaHigh concentration ofcones – photoreceptorsresponsible for visualacuity, constituting 15°of visual Veld.
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Reading
SaccadeBallistic eye movements that propel the eye to anotherVxation point.
Perceptual spanAsymmetric perceptual window during reading: 3–4 letters toleft; 7–8 to right.
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Reading Reading
Alexia
Pure alexiaRecognize letters as letters, butincapable of naming or using them torecognize words.
I Other visual and verbalcapacities are largely spared.
I Able to recognize numbers!I Damage to left occipto-temporal
area Joseph Jules Déjerine(1849–1917)
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Dehaene, 2009: Fig 2.1
Dehaene, 2009: Fig 2.1
$ “Why should all human beingshave this built-in facility forreading, when writing is arelatively recent culturalinvention?”
$ “How, then, did the visual wordform area of the human brainarise?”
Oliver Sacks(b. 1933)
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$ The brain constrains writingsystems by accepting only alimited types of symbols, thoseshared with other, moreancestral forms of visualprocessing. Thus, shared by allhumans – with natural, anduniversal, restrictions onorthographies.
Stanislas Dehaene(b. 1965)
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Writing response 4, due Friday, 19 AprilIn previous classes, we’ve discussed the role of biases incognition. According to Eagleman, biases are, to some extent,what makes us smart by providing some order in perceptualchaos. In the unit on language, we’ve seen examples of bias inword leaning - for example, the whole object bias. In yourresponse, please address the following three questions in 2-3single spaced pages:
(1) Can we say that biases encountered during languageacquisition also make us smart? (2) How about restrictionsthat seem to be imposed by our particular native language -for example, whether we have an exact (cardinal) or relativenumber system? (3) How are such restrictions similar ordiUerent than biases in terms of their cognitive eUect? Defendyour position by using concrete examples of biases andrestrictions from the readings to illustrate your point.