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