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Last Lecture

Last Lecture. Hemispheric differences in the Bisected Brain Functions of the corpus callosum Hemispheric Asymmetries in the Normal Brain Methods and theories. This Lecture. Dichotic Listening The corpus callosum & resource allocation Handedness Functions of the corpus callosum

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Last Lecture

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  1. Last Lecture • Hemispheric differences in the Bisected Brain • Functions of the corpus callosum • Hemispheric Asymmetries in the Normal Brain • Methods and theories

  2. This Lecture • Dichotic Listening • The corpus callosum & resource allocation • Handedness • Functions of the corpus callosum • The aphasias

  3. Announcements • Quiz next week • Study guide on the web after class today • Cognitive Neuroscience chapter 8 only sections on Language and the Brain (303-312)

  4. With dichotic input the ipsilateral ear’s input is supressed. Both ears project bilaterally Contralateral projection is stronger right left right left right left ga ga ga ba ba ba - - ga ba ba ga - Dichotic Listening

  5. The Corpus Callosum and Processing Resources • Resource: basic raw materials needed to get a task done. • Each hemisphere has some competancy with most tasks. • As task difficulty increases, both hemispheres are recruited to meet task demands.

  6. Two Comparison Conditions Within Field Comparison Across Field Comparison A B A B + + A A A B B A A A Unilateral Processing Bihemispheric Processing (fromBanich & Belger, 1989)

  7. A B A B A B C D C D + + + A A a Three Levels of Task Difficulty 3-Item Physical 5-Item Physical 5-Item Name Physical Identity Match: A-A Name Identity Match: A-a

  8. 750 WITHIN ACROSS 650 550 450 350 250 3-PI 5-PI 5-NI Sometimes, Two Hemispheres are Better than One... • For easier tasks within field matches are faster. • For harder tasks across field matches are faster. Reaction Time

  9. Functions of the Corpus Callosum • Unify the sensory world • e.g. copies of input • Information transmission • to access specialized processors (more on this with case V.J) • to share products of cognitive processes • Allocation of resources (Banich task)

  10. Handedness • 10% of the population is Left Handed • Left handers have different brain organization What is left-handedness?

  11. Case V.J.- Clues to handedness(Baynes et al) • a left hander w/ normal speech & language who underwent callosotomy. After surgery: • left hand single-letter writing - perfect • right hand entirely agraphic left hand right hand

  12. Left hand Right hand

  13. Isolation of grapho-motor module • In VJ, writing dissociates from other language abilities. • Writing in RH • All others LH • In JW & VP all language abilities are co-localized in LH.

  14. Implications of V.J. • Writing module can be dissociated from other language modules. • Handedness may depend on laterality of writing module. • In all Left handers access to this RH module may require the c. callosum. • Laterality of other language modules may also vary in Left handers.

  15. What are the other components of language?

  16. Components of Sound-based Language • Phonemes- units of sounds that make up words • Morphemes- smallest unit of meaning • Syntax - grammar-- rules for combining words • Lexicon - stored representations of words (auditory/visual) • Semantics - meanings that correspond to lexical items • Prosody- intonation of speech (Right Hemisphere province) • Articulation- movements of the mouth and vocal tract for producing speech • Discourse - Linking of sentences into coherent narrative. Production and comprehension of these components are required for language.

  17. Broca's aphasia • speech: labored, slow & nonfluent (awkward articulation, search for phonemes). • paraphasic errors (phonemic: pelsil for pencil) • responses make sense but are ungrammatical. • greatest difficulty: verbs, articles, pronouns (generating & repeating) --> telegraphic speech • Comprehension is relatively spared

  18. 44 39 22

  19. Cookie Theft Picture (BDAE)

  20. Lesion locus of Broca’s aphasia

  21. Is Broca’s aphasia simply a problem with vocal-motor coordination? After all...Broca’s area is near motor face area... NO!! • No dysfluency after hemifacial paralysis from RH damage • Dysarthria - a separate disturbance- lack of coordination of vocal track.

  22. Broca’s aphasia has cognitive/linguistic properties • Better fluency for memorized phrases. • Singing may be more fluent than speech • --> Melodic intonation therapy • Why should coordination problems affect verbs/function words more than nouns??? • Written output shows same errors as speech! These features suggest more than a problem with vocal coordination.

  23. Wernicke-Geschwind model • Broca's a.: forms detailed coordinated plans for language production (spoken, written, covert/rehearsal) • Explains dysfluency and poor articulation Butcomprehension is not perfect... • Schwartz, Saffran and Marin, 1980 • Poor syntax comprehension • Broca's aphasics poor at judging grammaticality Active: The horse kicked the cow. Passive: The cow was kicked by the horse.

  24. Agrammatism... • difficulty using & understanding grammar Modification of the W-G model Broca's area: • Plan for coordinating language production • understanding and using syntax. Active: The horse kicked the cow. Passive: The cow was kicked by the horse.

  25. 44 39 22

  26. Wernicke's aphasia • Speech: phonetically & grammatically normal but meaningless. • generally fluent, unlabored, well articulated. • normal intonation (prosody). • words used inappropriately, nonsense words (neologisms) --> "word salad" • meaning expressed in roundabout way (circumlocution). Cookie Theft description... • "Mother is away here working her work to get better, but when she's looking into the two boys looking in the other part. She's working another time..." • Comprehension: severely impaired.

  27. Interpretation of Wernicke's aphasia According to Wernicke-Geschwind model Wernicke's Area • stores memories of sound sequences that constitute words. • translates auditory input into phonological forms that can then access semantics. • meaning is stored in other cortical areas • During spontaneous speech, "cognitive" areas send input to Wernicke's area: • Cognition -> Wernicke's A. (22) -> arcuate fasciculus -> Broca's A. (44)-> Face area

  28. READING

  29. Reading According to theWernicke-Geschwind model... Wernicke’s A. essential for reading... • Visual processing --> Angular gyrus --> Wernicke's A.--> Semantics • Angular G. (39) translates visual code to a form that can access auditory word code in Wernicke’s.A. • Semantics must be accessed via the auditory (phonological) form of the word. • Implication: Reading requires phonological recoding via Wernicke’s area… or does it??

  30. PET evidence challenges this accountPosner, Peterson, Raichle and colleagues (1988) • If auditory recoding is necessary for reading then reading and listening should activate the same brain areas • They do not... • Implication- visual representation can access meaning directly LISTENING READING

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