Language PDF

Language - fundamental to what makes us human - Contributes to other high level cognitive functions - Executive functions - Reasoning - Mathematics - Arts and creativity LEFT HEMISPHERE AND LANGUAGE - damage to left hemisphere is more likely to cause impairments in speech and comprehension - Most r...

Language - fundamental to what makes us human - Contributes to other high level cognitive functions - Executive functions - Reasoning - Mathematics - Arts and creativity LEFT HEMISPHERE AND LANGUAGE - damage to left hemisphere is more likely to cause impairments in speech and comprehension - Most right-handed people have left-hemisphere speech (as do most left-handed) Handedness Cases Left Speech Bilateral Speech Right Speech Right 140 96% 0% 4% Left 122 70% 15% 15% HOW DO WE KNOW THIS? - Wanda test: one hemisphere is anaesthetized with short-acting drug & repeated for opposite hemisphere - fMRI during language testing: naming, verb generation, uency & compare the degree of activation in left and right hemispheres - L > R = left hemisphere speech - L = R = bilateral speech - R > L = right hemisphere speech Example: Patient TAN by Broca - could only say the word “tan” - Other abilities una ected - Autopsy revealed inferior frontal lesion BROCA’S APHASIA - non- uent aphasia - Characteristics: fl ffi ff ffi fl ffi 1. Produce few words with lot of di culty 2. Produce content words (nouns and verbs) 3. Few function words (conjunctions and prepositions) 4. Di culty with word endings (-ing, -ed, -s) 5. No paralysis of vocal musculature, can produce non-speech sounds (laugh, bark, etc) - normal comprehension for both written and spoken speech - What they say makes sense - Awareness of di culty -> lead to depression WERNICKE’S APHASIA - ability to speak but no understanding of language Speech does not make sense Many have damage to left temporal/parietal area Fluent aphasia: speech retains super cial structure, rhythm and intonation but is a meaningless jumble - Di culty with speech comprehension - May not be able to follow simple commas such as point to the blue square - Verbal paraphasia (word substitutions) - Semantic paraphasia: substituted word has a related meaning (barn for house) - Phonemic paraphasia: substituted words has a similar sound word (table for fable) - Neologisms: legal new words (“trable”) - Word sounds not linked to their meaning CONDUCTION APHASIA - some have damage to the white matter connections between Broca’s and Wernicke’s areas - Fluent speech: Broca is not damaged - Good comprehension: Wernicke is not damaged - But problems producing speech (paraphasia), especially repeating PROBLEMS WITH THE SIMPLE ONE REGION = ONE FUNCTION MODEL - some with damage to Broca have trouble with perception Some with damage to Wernicke have trouble with production These regions are connected, so damage to one can disrupt the function of the other Stroke, tumor and other injuries often damage parts of both regions and/or the connecting white matter - no brain region acts in isolation BRAIN REGIONS AND CONNECTIONS IMPORTANT FOR LANGUAGE DORSAL PATHWAY - SOUND TO ACTION - Auditory cortex – superior temporal gyrus • Primary auditory cortex (41), posterior (42), anterior (22) - Parietal – sensory to sensory, and sensory to motor transformations - Premotor – basic links between sound and action - Broca – inferior frontal gyrus, areas 44/45, pars opercularis/pars triangularis - Auditory regions connected to PMC and Broca through the arcuate fasciculus - Posterior auditory is connected to PMC through the parietal cortex • Articulation and language production - Additional connections from parietal to Broca - Also direct connections to Broca • More complex aspects of motor planning and sequencing related to grammar and syntax VENTRAL PATHWAY - SOUND TO MEANING fi ffi - Auditory cortex • posterior (42), anterior (22) - Also, areas 21, 37 • multimodal representations of voice and body (self and other) - Inferior temporal gyrus • Face, place and object representations • Relevant for words and meanings - Posterior auditory connected to other auditory and multimodal regions in the middle and inferior temporal gyrus • Connects to voice, body and object representations • Connections to visual areas relevant for reading - Anterior auditory regions connected directly to Broca via the uncinate fasciculus. • Direct link between meaning and grammatical structure EVOLUTION OF LANGUAGE PATHWAYS - Monkeys and apes have similar connections between auditory and anterior language regions • But ventral pathway is larger and both pathways L=R - In humans the dorsal pathway is larger and L>R - Suggests that language specialization in humans depends on • sophisticated auditory to motor transformations • The ability to sequence hierarchically and over time PSYCHOLINGUISTICS Psycholinguistics: Exploring how language functions in the brain based on its structure PHONOLOGY ff ff Phonology: how sounds in a language are organized - Certain sounds are common or uncommon – pa, ba in English, “d” vs “de” in Hindi, use of tones in Mandarin - Sounds of a language and rules for combining them - Phoneme: smallest unit of sound that alters meaning - /b/ and /p/ cause /bear/ and /pear/ to have di erent meanings - phonetics: how a speech sound is produced in di erent contexts - /p/ can be articulated in di erent ways, pot vs. spot - depends on precise control over articulatory muscles PHONOLOGY AND APHASIA - Anterior/Broca’s aphasics make: - phonetic errors – “f’teen” - phonemic errors – “six month” “my mother pass away” - Posterior/Wernicke’s aphasics have di culty selecting, sequencing, producing the correct phoneme - e.g., might substitute /b/ for /p/ (e.g., bear for pear or “estate spares”) - Produce neologisms – “good googin” - Suggests that phonetic vs. phonemic representations are partially separated - Because phonemes link sound to meaning - Explains receptive de cits - Also explains expressive de cits SYNTAX - BROCA’S AREA Syntax: rules of grammar - Past is formed with –ed in English, use a particle “de” in Mandarin - Noun – verb – object in English - Le drapeau national vs the national ag - rules for meaningful combinations of words Subject-Verb-Object common in English • “The police o cer chased the robber.” • exceptions: the passive voice, O-V-S: - “The robber was chased by the police o cer.” - Anterior lesions impair syntax • Telegraphic speech uses simple syntax (S-V-O) • Complex syntax is misinterpreted: O-V-S • Not sensitive to grammatical cues - Endings missing (-ing, -ed) - Pronouns missing (went school), possessives misused (mother instead of my mother) - Also poor comprehension of more complex syntax • “The cat chased the kitten.” vs. “The cat was chased by the kitten.” • But, okay for “The ice cream cone was eaten by the boy.” - Posterior lesions have less e ect on syntax • Wernicke’s aphasia produces meaningless, but grammatical speech SEMANTICS Semantics: rules, categories of meaning - Multiple words for snow in inuktituk, words that exist in one language but not in another - the meaning of words and word combinations - Posterior lesions impair the ability to extract meaning from language or to produce ffi ffi fl ff fi ff fi ffi meaningful speech - Problems with comprehension “point to the large circle” - Problems with production “me the circle on” - Anterior lesions impair syntax, but preserve meaning - Place the large red circle under the small blue square - Will make errors related to syntax, not semantics - Related to disruption of regions important for linking words and objects in the ventral stream ERP STUDY HE SPREAD JAM ON HIS WARM SOCKS - Semantic content is wrong - Syntax is correct - Posterior Broca’s area: greater negative response in brain (N400) - semantic error produce a L > R N400 over posterior - But not anterior language regions HE SPREADED BUTTER ON WARM TOAST - error in grammar/syntax - Semantic is correct - Bilateral (anterior + posterior) response: larger positive response - Relatively the same on L and R - syntactic (grammatical) errors produce a bilateral (L & R) N600 over both positive posterior and anterior language regions - Possibly because they change both the grammar and the meaning - Left: more important for grammar - Right: more important for - Response are about familiarity of the language PERCEPTION IS LINKED TO PRODUCTION - Listen to speech with scrambled visual input Watch lips or eyes with scrambled auditory input Listen to and watch scrambled input Use TMS over motor cortex to elicit a motor response from the muscles of the lips - If stimulate brie y and put electrodes at corner of the mouth - Lower threshold to get a signal that the muscles are active around the mouth is perceived something that makes the mouth prepared - Greater activity in Broca’s area when listening to speech is related to larger motor evoked potentials - Focusing on lips can help to understand - Processing of speech sounds in posterior regions “primes” or sends a signal to anterior regions - Listening to language is never entirely passive - automatically prepare the motor commands required to produce the sounds we hear WHAT DOES VISUAL LANGUAGE PROCESSING TELL US? - Sign language has a semantic and syntactic structure similar to spoken language - Speakers of sign language who su er damage to the left hemisphere language areas develop aphasia in their signed language ff fl - Sign language semantic violations generate an N400 (spread jam on warm socks) • Similar negative response to somatic errors BRAIN ACTIVITY WHEN PERCEIVING SIGN LANGUAGE - Speakers of both ASL and LSQ show activity in Broca’s area when viewing sentences in sign • Deaf ASL & Deaf LSQ: both posterior and anterior - Overlapping regions: auditory cortical regions - When hearing de cit, the auditory cortical regions get repurposed • No change in grey matter - These posterior language regions are specialized for language, regardless of modality - They also show activity in posterior auditory regions - These regions may be important for sequencing linguistic information - These patterns are the same for both languages BILINGUALISM: ONE REPRESENTATION OR TWO (OR MORE) Aphasia: - Left hemisphere damage produces impairments in speech • Older people where English is not their rst language might revert to speaking only their native language • Sometimes for both languages • Usually more for second language (L2) - May be dependent on when they learned the 2nd language (automatic or not) - Some brain stimulation data shows evidence for multiple representations • But, this may depend on stimulation level, words tested, degree of uency - Spanish/Catalan bilinguals vs monolinguals • Similar anterior language regions active for the two languages • Greater activation for 2nd language, even when performance is similar - May be more e ort/processing required even if there’s uency in both • Additional posterior regions active for 2nd language semantic tasks - Tasks tapping into meaning - Suggests that L2 processing is more e ortful - Fits with evidence that L2 is more susceptible to impairment following stroke - Also with evidence of L2 loss with aging and dementia BILINGUALISM: AGE OF ONSET Simultaneous vs sequential bilinguals - resting state functional connectivity (when not doing a task) between posterior and anterior language regions - Related to age of onset of L2 - The intrinsic between activity and 2 regions are di erent depending on when you acquired your 2nd language (not doing a task) - These regions were in the right hemisphere - Greater recruitment of right hemisphere regions fl fl ff fi ff fl fi ff - French/English bilinguals (equally uent) • Greater grey matter volume in L putamen for simultaneous • Greater grey matter volume in PMC for sequential • Volume of putamen and PMC related to accent score (rate their accent) • Grey matter changes related to the motor demands of speaking two languages