Cognitive Neuroscience Lecture 11: Language Lecture 1

''L11: Language Guest Lecture: Language in the brain—from fundamentals to applications''

Language in the brain

Language – A formal system for relating signals and meanings

• Language comprehension: signal à meaning

• Language production: meaning à signal

Language is distinct from speech, thought or communication

-         Language different from speech:

o Parrots & computers produce speech but not language

o Language communicated via speech or writing

-         Language different from thought

o Language verbalizes thought

o Bi-linguals express same thoughts in different languages

o Brain injury may damage language but you can still think

-         Language is different from communication

o Body language, math

Language Knowledge

-         Innate

o Critical periods: exposure during limited time in development (adolescence) is critical for normal devàprocess with its own “clock”

§ Children not exposed before adolescence fail to acquire it later

§ 2nd language harder when learned after adolescence

o Genetically linked to language deficits

§ Developmental language disorders not due to evident neural injury

-         2 sources of our language knowledge

o Genetic blueprint (innate neural/cognitive machinery)

§ Explains aspects of language that are the same across languages (universal grammar)

o Learning

§ Allows us to learn characteristics of specific language one is exposed to

·       Explains aspects of language that are different across languages

-         Language is productive

o Understand and produce infinite number of sentences never produced or heard before

o How?

§ System of rules (grammar) for combining elements (words)

o Rule system

§ Allows for sentences to be understood and produced similarly across ppl

§ Everyone has same definition for gramattical vs non

-         Language is multi-componential

o Multiple components specialized for processing different aspects of language knowledge

§ Semantics: word meanings

§ Syntax: word ordering

§ Phonology: word sounds

o Components used in comprehension and production of language

o Patterns of language ability and disability subsequent to neural injury

o Aphasia: language impairment

o Cases exhibit full range of double dissoc

§ phonology vs semantics

§ syntax vs semantics

Phonology: knowledge of language sounds

-         phonemes: smallest unit sound that distinguishes one word from another in a given language

o pot/pod

-         '''Phonological words (morphemes)''': combinations of sounds that comprise meaningful units

o Giraffe-s à2

o Un-happi-nessà3

-         Semantics: word meaning

o Semantics: our knowledge of the meanings of words that allows us to use and understand them appropriately

§ More complex than dictionary def

o Sweep vs. swept

-         Syntax: rules

o Knowledge of how words can be combined in ordered to express meaning

o English = SVO

Language network: overview

-         Fmri conditions: spoken and written stories vs. scrambled spoken/written stim

-         Perisylvian language areas

o   Frontal lobe: inferior frontal gyrus

o   Temporal lobe: superior and middle temporal gyri

o   Parietal lobe: supra-marginal and angular gyri

o Broca’s area: BA 44/45

o Wernicke’s area: BA 22

o

-         Language Lateralization: is it limited to left hem?

o Neuroanatomical asymmetries

§ Planum temporale: auditory processing region within Sylvian fissure

§ LH larger than RH in most right-handers (starts at 31st week of gestation)

§

o How are the language functions distributed across hemispheres?

o How can we find out?

§ Isolate the hemis

§ WADA

§ Commisurotomy

·       Separate hemis by cutting corpus callosum

·       Treats intractable epilepsy

·       Test hemis separately with 1 vis field presentation

§ Hemispherectomy

·       Surgical treatment for tumors and rasmussen’s syndrome

·       Affects RH or LH

-         Right Hemisphere Language?

o Limited and redundant (not necessary)

o Hemi differences between comprehension and production

§ Left: production

§ Right: comprehension

o Good recovery in response to early damage

§ Early damage shows right hemi’s latent language capacities

o Difference in neuroimaging and lesion studies in terms of right hemi involvement?

§ Lesion studies reveal necessary neural substrates (but not sufficient)

Phonological aspects of language processing:

Ventral: Comprehension: AudàSTGàMTG/ITGàATL

Dorsal: Production: STGàSptàSMGàIFG+PM

Ventral stream damage

-         Intact environmental sound identification, visual recognition, semantic knowledge

-         Impaired speech comprehension (discrim, ID, repetition of word he just heard, comprehension)

o Phoneme ID difficult

o Phonological word id difficult

Dorsal stream damage

-         Trouble with phon. Word selection, phoneme selection, motor planning

Evidence from defecits affecting semantic categories

-         Lesion locations associated with selective deficits in naming words from specific categories (people, animals, tools)

o Left middle and inferior temporal gyri

-         Evidence from voxel based morphometry

o Semantic dementia

§ Degenerative disease: loss of understanding of word meanings

§ Cortical atrophy

o Mummery et al:

§ VBM measures cortical thickness at each voxel

·       Atrophy left lateralized in anterior temporal lobe (temporal pole)

Using ERP to examine syntactic processing

-         How could we isolate syntactic processing in neuroimaging/disruption studies?

o Grammatical vs. ungrammatical sentences

o More complex vs. less complex

o Syntax but no semantics (jabberwocky)

-         Left anterior negativity characteristic ERP response after syntactic violation

-         Distribution over time and electrodes of differences in brain response to grammatical vs. ungrammatical word

o LAN at 450-500ms

o Early and later ERP identified at left anterior electrodes (left frontal cortex)

fMRI: sentences with and without meaning

-         Jabberwocky compared to just lists of nonword

-         Left IFG consistently associated w/ lesions affecting syntactic processing and activation studies

-         Other perisylvian language areas also associated w/ syntactic processing

-         Conclusions?

o H1: Syntactic processing distributed

o H2: we have not yet figured out how to isolate syntax from other aspects of language processing

Language network

-         Basic language processes

-         Neural substrates

-         Methods and results