Language and the Brain Understanding how language is represented and processed in the brain

Language and the Brain

Understanding how language is represented and processed in the brain

Psycholinguisics

The study of acquisition, storage, comprehension and production of language

Neurolinguistics: branch of psycholinguistics dealing with language and the brain

Cerebral cortex

Cerebral cortex: A one-quarter-inch thick membrane covering the brain– consciousness, thinking, learning, emotions,

language– Constitutes the difference between humans and

other animals

Corpus callosum: bundle of nerve fibers that connects the brain’s right and left hemispheres

LATERALIZATION

RIGHT HEMISPHERE

holistic reasoning music processing processing of non-

linguistic sounds visual, spatial

processing

LEFT HEMISPHERE

analytic reasoning temporal ordering arithmetic language processing

Each hemisphere specializes in diff. cognitive functions (referred to as lateralization)

Lateralization (Cont’d)

Most right-handersleft-hemisphere dominance for language

Left-handersgenerally less lateralized for language

Evidence of Lateralization:Language damage far more likely following left-hemisphere damage (70% vs. 1%)Dichotic listening testSplit-brain patients

Dichotic listening test

• Two different stimuli are presented simultaneously through earphones to the left and right ears

• The listeners are asked to say what they hear

threetwo

Which one do youthink is more

accurately reported?

Contralateralization

The connection between the brain and the body are almost completely contralateral

L s

ens

ory

info

rma

tion

R s

enso

ry in

form

atio

n

threetwo

The right ear advantage (REA)

Brain

BONES AND MUSCLES OF THE HEAD

threetwo

L

L earR ear

R

nonlinguisticsound

processing

languageprocessing

Listeners can identify linguistic stimuli more accurately when presented to their right ear.

two

The left ear advantage

Brain

BONES AND MUSCLES OF THE HEAD

Ha ha haZzzz

L

L earR ear

R

Listeners can identify nonlinguistic stimuli more accurately when presented to their left ear.

Riiing!

nonlinguisticsound

processing

languageprocessing

Split brain experiments

The hemispheres of the brain are connected by the corpus callosum

Corpus callosum severed to prevent severe seizures

In these experiments, patients are blindfolded and an object (let’s say a key) is placed in their right or left hand

Split-brain patients & language

BrainRL

key in left hand

Split-brain patients & language

BrainRL

key in right hand

Split Brain Experiments

KEY IN RIGHT HAND– Patient can name

object

KEY IN LEFT HAND– Patient unable to

name object

Broca’s area

FRONT

BACK

Angular gyrus

Language centers

Speech productionSyntactic info

Language comprehensionLexicon

Integrates visual & auditory infoCrucial for reading

Wernicke’s area

Language Disorders

A damage to one of these areas will affect the ability to produce/perceive language– Aphasia: – Broca’s Aphasia– Wernicke’s Aphasia

Broca’s area

Involved in speech production – motor programming for articulation

Involved in morphosyntactic analysis– Inflection– Structural complexity

Add grammatical refinements to content words selected in Wernicke’s area.

Sample speech: Broca’s aphasia•Examiner: Tell me, what did you do before you retired?•Aphasic: Uh, uh, uh, pub, par, partender,

no.•Examiner: Carpenter?•Aphasic: (Nodding to signal yes)

Carpenter, tuh, tuh, twenty year.

(Akmajian et al. 2001: p. 543)

Broca’s Aphasia and Syntactic Disorder Broca’s aphasics tend to omit inflectional morphemes

(-ing, -ed, -en, -s)—necessary for syntax Broca’s aphasics can’t determine grammaticality in

following sentences:– The boy ate it up.– * The boy ate up it.– * Boy ate it up.– The boy ate up the cake.

Broca’s Aphasia and Syntactic Disorder a. The mouse was chased by the cat. b. The cat was chased by the mouse Broca’s aphasiacs tend to interpret (a)

correctly, but they tend to give (b) the same interpretation as (a)

Our understanding of (a) and (b) is driven by syntax; a Broca’s aphasiac’s understanding is driven by semantics.

Wernicke’s area

Essential to language comprehension Involved in selection/evaluation of content

words (contained in lexicon)

Sample speech: Wernicke’s aphasia Examiner: Do you like it here in Kansas City? Aphasic: Yes, I am. Examiner: I’d like to have you tell me

something about your problem. Aphasic: Yes, I, ugh, can’t hill all of my

way. I can’t talk all of the things I do, and part of the part I can go alright, but I can’t tell from the other people. I usually most of my things. I know what can I talk and know what they are, but I can’t always come back even though I know they should be in, and I know should something eely I should know what I’m doing...

(Akmajian et al. 2001: p. 544)

Wernicke’s aphasia

Fluent, but their speech doesn’t make any sense.