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Chapter 14: Cognitive Functions. 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.
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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.
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.
Evolution and Physiology of Language • Human language is most likely a modification of a behavior also found in other species. • Chimpanzees use language but it differs from humans: • Seldom use symbols in new original combinations. • Use of symbols lacks productivity. • Use of symbols is primarily used to request and not describe. • Production of requests is better than understanding other’s requests.
Evolution and Physiology of Language • Bonobos or pygmy chimpanzees show an increased comprehension of human language: • Understand more than they can produce. • Use symbols and names to describe objects. • Request items not seen. • Use symbols to describe past events. • Make original, creative requests.
Lateralization of Function • Non-primates also display some aspects of spoken language. • Elephants imitate sounds they hear, including the vocalizations of other elephants. • Dolphins respond to gestures and sounds. • The African gray parrot show a great ability for imitating sounds and also using sounds meaningfully. • Example: Alex the gray parrot.
Evolution and Physiology of Language Studies of nonhuman language abilities: • Give insights to how best to teach language to those who do not learn it easily. • Examples: Brain damaged people or children with autism. • Illustrate the ambiguity of our concept of language. • Allows for more precise definition.
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 exists for the learning of language. • Learning of a second language differs as a function of age: • Children are better at learning pronunciation and unfamiliar aspects of grammar. • No sharp cutoff exist for second 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 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.
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).
Evolution and Physiology of Language • Dyslexia is a specific impairment of reading in a person with adequate vision and adequate skills in other academic areas. • More common in boys. • Research suggests a genetic influence.
Evolution and Physiology of Language • In some cases, dyslexia is associated with mild abnormality in the structures of various brain areas. • More likely to have a bilateral symmetrical cerebral cortex. • Language–related areas in the right hemisphere are larger in some. • Weak connections exist among other areas.
Evolution and Physiology of Language • Different kinds of dyslexics have different reading problems. • “Dysphonic dyslexics” have trouble sounding out words. • Attempt to remember them as a whole. • “Dyseidetic dyslexics” fail to recognize a word as a whole. • Read slowly and have particular trouble with irregularly spelled words.
Evolution and Physiology of Language • Most severe cases of “dyseidetic dyslexia” result from brain damage that restricts the field of vision. • Characterized by the following: • only seeing one letter a time. • short eye movements. • very slow reading. • difficulty with long words.
Evolution and Physiology of Language • One hypothesis to explain dyslexia emphasizes a hearing impairment rather than visual impairment. • Less than normal response to speech sounds in the brain. • Lack of ability to pay close attention to sounds.
