Lecture 9- Neuroscience of language

Question 1

What is language?

Answer 1

-auditory, visual, or tactile symbols for communication -has a grammar and lexicon (an arbitrary meaning for each element -all are symbolic= agreed meaning -grammar= also agreed on

Question 2

Is language specialised and separate from other pathways?

Answer 2

-yes, language processors are highly specialised and separate to rest of auditory pathways

Question 3

Is there much knowledge on language and its pathways?

Answer 3

-Language is one of the most accessible higher functions -Much work has been done to understand where in the brain language ability resides -Insights depend on strokes (initially) and split brain and fMRI (more recently) -don’t know much about the circuitry, very complicated and changeable between people it seems

Question 4

What functions must a hypothetical language network do?

Answer 4

-must be able to detect and to generate: 1. Phonemes: Distinct sounds that make up words (“p”, “b”) 42 in English (25 consonants, 17 vowels) 2. Graphemes: written symbols that represent spoken sounds 3. Words: objects, concepts, actions, properties and logical connectives 4. Sentences: complexes of words whose relationships determine meaning (syntax) 5. Discourse: higher order structure made of sentences

Question 5

What is characteristic of neural pathways underlying language?

Answer 5

1. Language processors highly specialised and separate to rest of auditory pathways 2. “On” permanently. Can’t choose to hear language as just noise 3. Operate unconsciously 4. Incredibly fast: recognise individual words in less than 125 ms (while they are still being spoken), massively parallel 5. Develops automatically: doesn’t require “learning” (c.f. written language

Question 6

What does the language network look like in a brain, both the old textbook version and the new version?

Answer 6

• each dot represents where language is
• so the old way of seeing it is not true
• not the same in each person, where I have nouns other may not
• widely dispersed across temporal and frontal lobes (also into parietal and occipital lobes)

Question 7

Where is the damage in the cortex to have Broca’s aphasia?

Answer 7

• compare lesion distribution in strokes with and without Broca’s aphasia
• insula cortex is the key area for deficit, deep to Broca’s area

.-broca’s aphasia is not in the broca’s area, it is in the insular cortex

• pic:used to be broca’s aphasia
• the darker bits are the ones more common in stroke people with broca’s aphasia

Question 8

What is the connection between the cerebellum and language?

Answer 8

-cerebellum mainly thought to have a motor role in language-seen in ataxic dysarthria (problems speaking when damage to cerebellum) -poor production of vowels and consonants, problems with stress and voice quality (when have ataxic dysarthria) -BUT seems that more than articulation is impacted -word retrieval depressed after cerebellar damage -syntax impaired (string words together with meaning within them) -error checking impaired (like motor role of cerebellum) -other cognitive processes affected as well -right hemisphere damage the worst (this is the opposite to the cortex, you don’t want right cerebellum damaged!)

Question 9

How many people are right handed?

Answer 9

-90% of people are right handed, controlled by dominant left hemisphere

Question 10

Where is language centred in most people?

Answer 10

-in 96% of right handers and 70% left handers have language centred in the left hemisphere (93% of everyone when averaged) -other left handers have language in both hemispheres, only rarely in right -probability of right hemisphere language dominance is proportional to degree of left-handedness

Question 11

What are the cliche descriptions of the left and right hemispheres?

Answer 11

-left: dominant, verbal, analytic and intelligent -right: nondominant, nonverbal, visuospatial, holistic and creative -don’t want a stroke in the left hemisphere -this is very oversimplified

Question 12

How is it with lateralisation of language in split brain patients?

Answer 12

-fluent speech is a property of left hemisphere -Vicki’s right hemisphere could speak (a girl…. a woman) -among split brain patients, Vicki is one of a few who have ability to interact via language in the right brain -three to four can speak, a few more can read in the right hemisphere

Question 13

Why is Vicki exceptional?

Answer 13

vicki is very unusual= have a speaking right hemisphere, extremely exceptional

Question 14

How long after surgery could the very few split brain who can speak with their right hemisphere speak?

Answer 14

-Vicki’s right brain could speak soon after surgery, Joe took ten years for the right brain to speak -the few right hemisphere readers recognise written word but can’t convert graphemes to phonemes -have little understanding of grammar (Vicki shows some understanding)

Question 15

What language tasks can right-hemisphere do?

Answer 15

in a few (split brain patients mostly): -can read and understand numbers, letters, short words, Has a rich lexicon and can understand propositional speech -can produce non-propositional speech (days of the week, nursery rhymes, counting, swearing) -can’t produce propositional speech , can point to objects shown to left visual field or spoken into right ear but can’t speak their name -identifies known words by direct recognition not phonology, better at concrete words not abstract (imageability important), only see the symbol of the letter -in most: -no evidence of ability to carry out lexical, syntactic or semantic tasks

Question 16

What language tasks can the right hemisphere do in most people?

Answer 16

-no evidence of ability to carry out lexical, syntactic or semantic tasks 1. interpret and produce prosody (tone or emotional content of speech-very important) 2. gives us an ability to interpret metaphors (non-literal language, stroke to RHS can lead to literal interpretation of metaphor (I cried my eyes out) 3. Interpret humour, damage to RHS leads to difficulty interpreting punch lines and preference for slapstic 4. interpret non verbal sounds (dog barking etc)

Question 17

Why is the capacity of the language network amazing?

Answer 17

-novel, complex information easily conveyed and understood -knowledge of multiple languages possible -acquires as a child when motor and cognitive performance very immature -best to learn language at 2-3 years of age

Question 18

How many words does a baby know at 13, 17 and 24 months?

Answer 18

1. 13 months= 10 words 2. 17 months= 50 words 3. 24 months= 300 words (after hitting the 2 year mark pick up the pace)

Question 19

What is the rate of acquisition of words in children?

Answer 19

-early about 1 to 3 words a week -after 40 or so words 8 to 10 words a week -preschool and primary school: 10 words a day (one word every 2.5 hours)

Question 20

What is the average adult vocabulary?

Answer 20

-40 000-70 000 -that is on average 2 words for every day of your life

Question 21

What can infants hear that adults can’t?

Answer 21

-foreign language sounds and structure hard for an adult -infants (below 1 year of age) can detect the structure and sounds of all languages equally -at 1 year of age you can hear everything -as an adult cannot say or hear mandarin or japanese sounds of not native

Question 22

What is the critical period for language acquisition?

Answer 22

-second half of first year is critical -something happening then, infants begin to specialise in their language

Question 23

WHat was the language acquisition experiment with US and Mandarin kids?

Answer 23

-expose 9 month US infants to Mandarin (via person or television) for one month -performance identical with children raised from birth in Mandarin, but only for personal interaction not for TV

Question 24

When do infants specialise in their language that is in the environment?

Answer 24

between 7 and 12 months

Question 25

What are all languages considered by infants prior to 7 months of age?

Answer 25

-treat all languages as equal

Question 26

How can infants reocognise words?

Answer 26

-speech is a continous stream of sound (no breaks between words) -how can infants recognise the beginnings and ends? -they map “transitional probabilities” (these sounds are together often so a word, the ones that are not together then not a word and must be a boundary -depends on phoneme always following another in a particular word, but much more random which phonemes span word boundaries

Question 27

What is the development of language in utero?

Answer 27

-prosodic (emotional) cues learnt before word meaning -starts in utero-at birth -babies: -prefer speech in their mother’s language -prefer their mother’s speech over other females -prefer stories with a distinct rhythm and tempo that their mother read out loud during the last ten weeks of pregnancy -last few months in utero= part of language learning

Question 28

What is “motherese”?

Answer 28

-parents talk to infants in a language that is high pitched, slower tempo, exeggarated intonations (increase acoustic separation of word elements), exaggerates features that are critical to particular language (mandarin motherese emphasises four tones critical to word meaning) -infants prefer motheres, helps them learn the language

Question 29

When do the motor patterns for language develop and how?

Answer 29

-speech production develops before language understanding -infants of all language groups sound the same initially, language specific sounds by two years -speech motor patterns are laid down at this stage and are permanent (accents= your accent stays, hard to override later in life)

Question 30

How does the language learning ability compare in babies and adults and how does the ability develop over time?

Answer 30

-adults smarter than infants but infants much better at learning a language -two to three languages easily learnt during critical period early in life -ability to acquire a second language declines with age, most rapidly at puberty -existing language interferes with new language -neural pathways become specialised for one language, no longer plastic -language learning at later life incredibly hard for some reason

Question 31

What normally happens to adults with LHS stroke?

Answer 31

-permanent language disorders

Question 32

What happens to children with LHS stroke?

Answer 32

-normally develop normal language abilities -if a child at 4 years old has a stroke in the LHS, then develop perfect speech -in the RHS -why?

Question 33

What is a hemispheroctomy and why is it performed?

Answer 33

-the removal or disconnection of one hemisphere form the rest of brain -in young children a range of congenital and acquired conditions can lead to the need for this surgery -half the time it is the left hemisphere (have a look on how it affects language, their intelligence is not affected, partially paralysed on one side but has pretty good movement)

Question 34

What was the setup of the hemispheroctomy study?

Answer 34

-six patients (very few) -3 LHS, age at operation: 4, 11,12 -3 RHS, age at operation: 4, 12, 12 -current age: 15,14,15 and 12, 21, 23 -controls (21-32 y.o.) -fMRI study

Question 35

What were the result of the hemispheroctomy study the RHS part of the patients?

Answer 35

-presented with nouns and asked to generate a semantically related word (butter-bread) -both Broca’s and Wernicke’s seeon on LHS -as expected

Question 36

What were the result of the hemispheroctomy study the LHS part of the patients?

Answer 36

-is there a broca’s -part of RHS Broca’s lit up in one patient as a mirror representation of the LHS (only 3 patients) -other areas of RHS involved in other two patients

Question 37

What were the questions about the hemispheroctomy study?

Answer 37

-both RHS and LHS lit up in controls for this task -needed a more LHS dominant task (syntactical analysis?) -how does RHS take over language -three theories

Question 38

What are the 3 hypotheses about how the RHS takes over language in LHS hemispheroctomy patients?

Answer 38

H1: Both sides start off with bilateral language network, contract back to LHS with age H2: Language in children involves more than traditional language areas. These areas continue to be involved in hemispheroctomy patients H3: Areas of cortex that are never involved in language become active when language network lost.

Question 39

How to see which hypothesis is true?

Answer 39

-can go back to young children and see what hemisphere lights up -difficult to experiment with young kids as subjects need to follow instructions and produce appropriate responses

Question 40

What did the study looking at lateralisation in normal children determined?

Answer 40

-study examined 5-19 y.o. -used test that showed object and asked them to think of an action associated with the object (not vocalised) -demonstrated that left laterasition increases with age -fits mix of hypotheses 1 and 2

Question 41

How does the lateralisation of language change with age?

Answer 41

-both hemispheres changed -left hemisphere went from diffuse labelling (young) to deined Broca’s area (old) -right hemishere went from diffuse to nothing -in the young children both sides of the brain seem to be invilved in language

Question 42

How is language plastic in the brain?

Answer 42

-early language bilateral and distributed -later becomes left sided and more restricted -lose left hemisphere early enough and distributed language system can persist on right side -note hemispheroctomy patient have problems which may make them a bad model (brain affected by chronic epilepsy, operation often after main period of language acquisition, numbers are very low)

Question 43

Do people born with non-functional retinae still have cortical visual system?

Answer 43

-yes -tested with fMRI -language stimuli sentences, nonsense sentences, word lists, non-words lists -answered true/false questions about stimuli or whether a particular sound/word was present in stimuli -imaged while listening to stimuli -people who born blind or go blind -retinal blindness= never ever see -raised only with auditory sense

Question 44

What happens in the occipital lobe of blind people?

Answer 44

-what happens in the occipital lobe (usually for vision) - and in blind people the occipital lobe active during language tasks -when more language like the stimulus the more activity in the occipital lobe -blind people turn the occipital lobe to language -it is the left occipital lobe that is language dominated -it is left hemisphere language people -why is it left? -this is the closest piece of cortex

Question 45

Is language a proof of cortical plasticity?

Answer 45

-in this example only left visual cortex was used for language, why? -also used for other non-language tasks -suggests that language circuits may not be as specialised as thought, but use generic cortical modules that can also function in other roles

Question 46

What about sign language?

Answer 46

-language centres are specialised for symbols, not just heard and spoken language -one theory says language evoved initially as a signed (nonverbal) language, that is why we epmhasise speech with our arms -can get Wernicke’s and Broca’s aphasias for sign language -the language cirfcuit is the same if sign, braille and language, -doesn’t matter -the deaf communicate with sign language -uses similar areas of brain to speech -sign language separate from pantomine -similar roles for left and right hemisphere in signers -deaf children go through same stages with signing as do speaking children (babbling gives way to meaningful signs)