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 3: physiology 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.
Evolution and Physiology of Language • Two categories of theories attempt to explain the human ability to learn language more easily than other species. • “Language evolved as a by-product of overall brain development.” • “Language evolved as an extra part of the brain.”
Evolution and Physiology of Language • Problems associated with the “language as a by-product of increased intelligence” theory: • People with a full-size brain and normal overall intelligence can show severe language deficits. • People with impaired intelligence can have normal language skills. • Williams syndrome characterized by metal retardation but skillful use of language.
Evolution and Physiology 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.
Evolution and Physiology of Language • 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.
Evolution and Physiology of Language • 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.
Evolution and Physiology of Language • 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.
Evolution Anatomical control of breathing (aquatic theory) Developmental 1-word holophrase 2-word slot grammar native language grammar Animal models Chimpanzee - gesture Parrot - oral
Animal models Parrot - oral
Evolution and Physiology of Language • 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.
Evolution and Physiology of Language • 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).
Evolution and Physiology of Language • 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.
fMRI records of speech Fig. 14-16, p. 436
Evolution and Physiology of Language • 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.
Evolution and Physiology of Language • Typical characteristics of Wernicke’s aphasia include: • Articulate speech / fluent speech except with pauses to find the right word. • Difficulty finding the right word - anomia refers to the difficulty recalling the name of objects. • Poor language comprehension - difficulty understanding spoken and written speech (especially nouns and verbs).
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.
Lateralization of Function • 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.
Lateralization of Function • 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.
Lateralization of Function • 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.
Lateralization of Function • 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.
Lateralization of Function • 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.
Lateralization of Function • 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.
Lateralization of Function • 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.
Lateralization of Function • 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.
Lateralization of Function • 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.
Lateralization of Function • 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.
Lateralization of Function • 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.
Lateralization of Function • 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.
Lateralization of Function • 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.
Lateralization of Function • 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.
Lateralization of Function • 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.
Lateralization of 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.
Lateralization of Function • 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.