Language and lateralization Lecture 5 (Chapters 8 and 9)
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Transcript of Language and lateralization Lecture 5 (Chapters 8 and 9)
Language and lateralization
Lecture 5 (Chapters 8 and 9)
Last week
• We did some basic memory experiments
• We tried to locate memory in the brain and to relate brain lesions to amnesia
• We also explored executive functions in the frontal lobes
This week
• We will look at:– Aphasia– Speech production and perception– Language, its origins– … and the brain– Lateralization
• This covers chapters 8 and 9 (ends at page 369)
Examples of exam questions
• What is the role of the hippocampus in memory?
• Describe what to expect with patients who have bilateral lesions of the hippocampus.
• Describe three different ways in which brain lateralization has been studied
• Mention some reasons why speech perception is difficult
Neuroanatomical questions
• Draw as accurately as possible where Broca’s and Wernicke’s areas are located?
• Which part of the brain is anterior?
Broca’s aphasia
Wernicke’s aphasia
Relative location of language areas
Early model of language in the brain
Schematic model (oversimplified)
Broca Wernicke
Concepts
What is speech?
• Speech are modulated wave forms that are produced by a source (lungs and glottis) and filtered by the vocal tract and lips and cheeks
Source-filter model of speech
Speech production
English vowels: formants
o
a
The position of the articulatory organs during production of the vowels ah and oh
Speech perception is very difficult
Understanding language is even more difficult
Language is hierarchical and can be extremely ambiguous
Willem Levelt’s model of speech production and perception
From concept to speech signal
Very complicated transformation take place during speaking
• A conceptual representation is a network of neurons that fire with a complex associative correlational pattern
• This conceptual-semantic pattern is transformed into a hierarchical syntactic pattern
• This pattern is transformed into a serial speech pattern
Semantic networks may be used to help think about the associative networks in the brain
Better is it to view concepts as vectors of abstract ‘features’
Where does language come from? • Certain aspects of the development of language
and thought appear to be universal in that they – (i) preceed any learning by the individual
– (ii) are found in all individuals in the same way
• These universalia are often of a deep and abstract nature
• It is not known at present how they are respresented in the brain, or how they emerge from brain organization
Universal constraints in thought development
• Spelke shows that from a very early age, infants know about the continuity and solidity of objects
• These constraints lie at the core of the developmental learning system
• It is not clear how these are represented in the brain or how they emerge
Biological origins of language
• Why do we have language?
• Co-evolution of ‘memes’ or cultural products, which uses language as a carrier?
• What is language?
What is language?
• De Saussure distinguished ‘langue’ from ‘parole’
• Chomsky distinguished ‘competence’ from ‘performance’
• Chomsky strongly defended the idea of the innateness of language
Grammar may be innate
The essence of grammar is recursion
Simple grammar
G = {N,V,S,P}
S aSaS bSbS c
E.g., c, aca, bcb, aacaa, aabacabaa
S aSa aaSaa aabSbaa aabaSabaa aabacabaa
The man lit his awful sigar
The man that you thought was old lit his awful sigar
The man that you thought that your mother had seen lit his awful sigar
et cetera
It allows an infinite number of sentences to be generated by just a few rules
Creoles and the origins of language
• Creoles are based on pidgins
• A pidgin is not a uniform language
• A pidgin is not a complete language
• Creoles are strikingly similar all over the world
• Creoles probably emerge in a single generation
• Creoles emerge spontaneously
Hatian creole
Li maché He walked
Li té maché He had walked
L’av(a) maché He will/would walk
L’ap maché He is/was walking
Li t’av(a) maché He would have walked
Li t’ap maché He was/had been walking
L’av ap maché He will/would be walking
Li t’av ap maché He would have been walking
Selection versus instruction
• Chomsky/Pinker: The child must select a grammar
• Bickerton: The child is provided with a specific grammar, which it than modifies in the direction of the caretaker’s language
Conclusion: Not all languages may be equally hard to learn
• Children’s errors when learning English often resemble creole, for example, the so called double negative
• Perhaps, creole is the ‘original mother language’
Where is language located in the brain?
PET data corroborate the lesion data
How can semantic organization be organized according to category?
• Self-organizing maps in the brain can explain the emergence of topological mappings
• Examples are: – the somatosensory homunculus (discussed in
lecture 7)– retinotopic maps in V1 (area 17, discussed in
lecture 3)
Semantic organization can emerge on the basis of word context (Ritter and Kohonen, 1990)
Interesting is that words organize into both semanticand grammatical categories
Example of a semantotopic map
Lateralization of brain function
There are several ways to investigate brain lateralization
• Split-brain patients
• Amytal testing
• Dichotic listening and other lateralized experimental procedures
Split brain patients offer important insights into lateralization
Communication between the hemispheres can be investigated
With amytal testing one hemisphere is anesthetized
Dichotic listening is a ‘normal’ experimental procedure
Left-brain may attend more to detail, righ-brain more to contour
Right brain is faster for global stimuli
Left brain is faster for local stimuli
‘Level of detail’ may be defined through spatial frequency
Next week...
• Motor control
• Population coding
• Chapter 10