Evolution and Physiology of Language Human language is a complex form of communication. Compared to...

19. Language and Lateralization

Language

Evolution

Anatomical

Developmental

Animal models

Neurology

Broca’s area

Wernicke’s area

Language and memory

Lateralization

Anatomy

Function

Evolution and Physiology of Language

• Human language is a complex form of communication.

• Compared to other species, human language has high productivity.– Productivity - the ability to produce new signals

to represent new ideas.

Stroop Effect 1: read the words

Stroop Effect 2: name the colors

Although the functions of the anterior cingulate are very complex, broadly speaking it acts as a conduit between lower, somewhat more impulse-driven brain regions and higher, somewhat more thought-driven behaviors. The Stroop effect's sensitivity to changes in brain function may be related to its association with the anterior cingulate.

Stroop Effect 3: physiology


Language

Evolution

Anatomical

Developmental

Animal models

Neurology

Broca’s area

Wernicke’s area

Language and memory

Lateralization

Anatomy

Function


• Two categories of theories attempt to explain the human ability to learn language more easily than other species.1. “Language evolved as a by-product of overall

brain development.”2. “Language evolved as an extra part of the

brain.”


• Problems associated with the “language as a by-product of increased intelligence” theory:1. People with a full-size brain and normal

overall intelligence can show severe language deficits.

2. People with impaired intelligence can have normal language skills.

• Williams syndrome characterized by metal retardation but skillful use of language.


• Evidence suggesting language evolved as an extra brain module specialization includes:– Language acquisition device is a built in

mechanism for acquiring language.• Evidence comes from the ease at which most

children develop language.

– Chomsky (1980) further suggests the poverty of stimulus argument: children do not hear many examples of some of the grammatical structures they acquire.


• Most researchers agree that humans have a specially evolved “something” that enables them to learn language easily.– Certain brain areas are indeed necessary for

language.– But same areas are also necessary for other

tasks (memory and music perception).

• Exactly how humans evolved language is unknown but is perhaps due to the pressure for social interaction.


• Research suggests a critical period for learning language.

• Learning a 2nd language differs with of age:– Children are better at learning pronunciation

and unfamiliar aspects of grammar.

• No sharp cutoff for 2nd language learning:– Adults learn a second-language vocabulary

better.


• Rare cases of children not exposed to language indicates limited ability to learn language later.

• Deaf children unable to learn spoken language and not given the opportunity to learn sign language while young reveals:– Little development of skill at any language

later.– Early exposure to some language increases

ability to learn another language later.

EvolutionAnatomical

control of breathing(aquatic theory)

Developmental1-word holophrase2-word slot grammarnative language grammar

Animal modelsChimpanzee - gestureParrot - oral

Animal modelsParrot - oral


Language

Evolution

Anatomical

Developmental

Animal models

Neurology

Broca’s area

Wernicke’s area

Language and memory

Lateralization

Anatomy

Function


• Most knowledge of brain mechanisms of language come from the study of people with brain damage:– Broca’s area is a part of the frontal lobe of the

left cerebral cortex near the motor cortex.• Damage results in some language disability.

– Aphasia refers to a condition in which there is severe language impairment.


• Broca’s aphasia/nonfluent aphasia refers to serious impairment in language production, usually due to brain damage.

• Omission of most pronouns, prepositions, conjunctions, auxiliary verbs, tense and number endings during speech production.

• People with Broca's aphasia have trouble understanding the same kinds of words they omit (prepositions and conjunctions).


• Broca’s aphasia is usually accompanied by comprehension deficits when: – The sentence meaning depends on prepositions,

word endings or unusual word order.– Sentence structure is complicated.

• Broca’s area thus seems to be critical for the understanding of some, but not all, aspects of grammar.

Fig. 14-15, p. 435

Fig. 14-16, p. 436

fMRI records of speech


• Wernicke’s area is an area of the brain located near the auditory part of the cerebral cortex.

• Wernicke’s aphasia is characterized by the impaired ability to remember the names of objects and also impaired language comprehension.– Sometimes called “fluent aphasia” because the person

can still speak smoothly.

• Recognition of items is often not impaired; ability to find word is impaired.


• Typical characteristics of Wernicke’s aphasia include:1. Articulate speech / fluent speech except with

pauses to find the right word.2. Difficulty finding the right word - anomia

refers to the difficulty recalling the name of objects.

3. Poor language comprehension - difficulty understanding spoken and written speech (especially nouns and verbs).

Table 14-1, p. 438

Lateralization of Function

• Lateralization of function refers to the idea that each hemisphere of the brain is specialized for different functions.

• Each hemispheres controls the contralateral (opposite) side of the body.– Example: skin receptors and muscles mainly on

the right side of the body.– Each hemisphere sees the opposite side of the

world.


• The left and right hemisphere exchange information primarily through a set of axons called the corpus callosum.

• Other areas that exchange information include:– The anterior commissure.– The hippocampal commissure.– A few other small commissures.

• Information crosses to the other hemisphere with only a brief delay.

Fig. 14-2, p. 418


• The two hemispheres are not mirror images of each other.

• Division of labor between the two hemispheres is known as lateralization.– In most humans the left side is specialized for

language.

• The corpus callosum allows each hemisphere of the brain access to information from both sides.


• Each hemisphere of the brain gets input from the opposite half of the visual world.

• The visual field is what is visible at any moment.• Light from the right half of the visual field shines

into the left half of both retinas.• Light from the left visual field shines onto the

right half of both retinas.


• The left half of each retina connects to the left hemisphere.

• The right half of each retina connects to the right hemisphere.

• Half of the axons from each eye cross to the opposite side of the brain at the optic chiasm.

• The auditory system is arranged differently in that each ear sends the information to both sides of the brain.

Fig. 14-3a, p. 419


• Damage to the corpus callosum interferes with the exchange of information between hemispheres.

• Epilepsy is a condition characterized by repeated episodes of excessive synchronized neural activity.– Mainly due to decreased release of the inhibitory

neurotransmitter GABA.

• Physicians once cut the corpus callosum to prevent the seizure from spreading to the opposite side of the body.


• People who have undergone surgery to the corpus callosum are referred to as split-brain people.

• Spit brain people maintain normal intellect and motivation but they tend to:– Use hands independently in a way others

cannot.– Respond differently to stimuli presented to only

one side of the body.

Fig. 14-4, p. 420


• Sperry (1974) revealed subtle behavioral differences for spilt brain people.

• Because the left side of the brain is dominant for language in most people, most split brain people:– Have difficulty naming objects briefly viewed in the

left visual field.

• A small amount of information can still be transferred via several smaller commissures.

Fig. 14-5, p. 422


• Immediately after surgery, each hemisphere can only quickly and accurately respond to information that reaches it directly. – Smaller commissures allow a slower response.

• The brain later learns use the smaller connections:

• Difficulty integrating information between both remains.

Fig. 14-6, p. 423


• Right hemisphere is better at perceiving emotions.• Damage to parts of the right hemisphere causes

difficulty perceiving other’s emotions, failure to understand humor and sarcasm, and a monotone voice.

• Left hemisphere damage increases ability to accurately judge emotion.– Associated with decreased interference from the left

hemispheres.


• The right hemisphere is also better at comprehending spatial relationships.

• In general, the left hemisphere seems to focus more on visual details, and the right hemisphere focuses more on visual patterns.


• Some anatomical differences exist between the hemispheres of the brain.

• The planum temporale is an area of the temporal cortex that is larger in the left hemisphere in 65% of people.– Difference are slightly greater for people who are

strongly right handed.

• MRI studies indicate that the a big difference in the ratio of left to right planum temporale is related to increased language performance.

Fig. 14-9, p. 425


• Damage to left hemisphere often results in language deficiencies.

• Left side seems to be specialized for language from the very beginning in most people.

• The corpus callosum matures gradually through the first 5 to 10 years.– Thus, young children have difficulty comparing

information from the left and right hand.


• Being born with a condition where the corpus callosum does not completely develop results in extra development of the following:– Anterior commissure - connects the anterior parts of the

cerebral cortex.

– Hippocampal commissure - connects the left and right hippocampus.

• Allows performance on some tasks that differs from split-brain people.


• The left hemisphere is dominant for speech in 95% of right-handed people.

• Most left-handers have left-hemisphere or mixed-dominance for speech.– Few people have strong right hemisphere

dominance.


• Recovery of language after damage to the brain varies.

• Age affects extent of recovery.– Brain is more plastic at an early age.

• Right hemisphere reorganizes to serve some of the left-hemisphere function.


• Rasmussen’s encephalopathy is a rare condition in which the immune system initially attacks the glia and then the neurons of one hemispheres of the brain.– Usually begins in childhood or adolescence.

• Surgeons eventually remove or disconnect the side of the damaged brain.

• Language recovers slowly but substantially.– Slow deterioration allows the other side of the brain to

compensate and reorganize.


• Language recovery after brain damage is also influenced by how language was initially lateralized for the given person.

• Individuals with partial representation of language in both hemispheres recover better than those with language dominance in one hemisphere.

Evolution and Physiology of Language Human language is a complex form of communication. Compared to...

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