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Chapter 14:
Cognitive Functions
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Lateralization of Function
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Lateralization of function refers to the idea that each hemisphere of the brain is specialized for
different functions.
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Each hemispheres controls the contralateral (opposite) side of the body.
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Example: skin receptors and muscles mainly on the right side of the body.
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Each hemisphere sees the opposite side of the world.
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Lateralization of Function
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The left and right hemisphere exchange information primarily through a set of axons called the
corpus callosum.
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Other areas that exchange information include:
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The anterior commissure.
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The hippocampal commissure.
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A few other small commissures.
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Information crosses to the other hemisphere with only a brief delay.
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Lateralization of Function
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The two hemispheres are not mirror images of each other.
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Division of labor between the two hemispheres is known as lateralization.
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In most humans the left side is specialized for language.
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The corpus callosum allows each hemisphere of the brain access to information from both sides.
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Lateralization of Function
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Each hemisphere of the brain gets input from the opposite half of the visual world.
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The visual field is what is visible at any moment.
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Light from the right half of the visual field shines into the left half of both retinas.
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Light from the left visual field shines onto the right half of both retinas.
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Lateralization of Function
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The left half of each retina connects to the left hemisphere.
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The right half of each retina connects to the right hemisphere.
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Half of the axons from each eye cross to the opposite side of the brain at the optic chiasm.
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The auditory system is arranged differently in that each ear sends the information to both sides
of the brain.
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Lateralization of Function
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Damage to the corpus callosum interferes with the exchange of information between
hemispheres.
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Epilepsy is a condition characterized by repeated episodes of excessive synchronized neural
activity.
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Mainly due to decreased release of the inhibitory neurotransmitter GABA.
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Physicians once cut the corpus callosum to prevent the seizure from spreading to the opposite
side of the body.
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Lateralization of Function
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People who have undergone surgery to the corpus callosum are referred to as split-brain
people.
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Spit brain people maintain normal intellect and motivation but they tend to:
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Use hands independently in a way others cannot.
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Respond differently to stimuli presented to only one side of the body.
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Lateralization of Function
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Sperry (1974) revealed subtle behavioral differences for spilt brain people.
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Because the left side of the brain is dominant for language in most people, most split brain
people:
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Have difficulty naming objects briefly viewed in the left visual field.
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A small amount of information can still be transferred via several smaller commissures.
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Lateralization of Function
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Immediately after surgery, each hemisphere can only quickly and accurately respond to
information that reaches it directly.
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Smaller commissures allow a slower response.
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The brain later learns use the smaller connections:
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Difficulty integrating information between both remains.
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Lateralization of Function
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Right hemisphere is better at perceiving emotions.
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Damage to parts of the right hemisphere causes difficulty perceiving other’s emotions, failure to
understand humor and sarcasm, and a monotone voice.
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Left hemisphere damage increases ability to accurately judge emotion.
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Associated with decreased interference from the left hemispheres.
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Lateralization of Function
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The right hemisphere is also better at comprehending spatial relationships.
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In general, the left hemisphere seems to focus more on visual details, and the right hemisphere
focuses more on visual patterns.
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Lateralization of Function
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Some anatomical differences exist between the hemispheres of the brain.
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The planum temporale is an area of the temporal cortex that is larger in the left hemisphere in
65% of people.
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Difference are slightly greater for people who are strongly right handed.
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MRI studies indicate that the a big difference in the ratio of left to right planum temporale is
related to increased language performance.
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Lateralization of Function
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Damage to left hemisphere often results in language deficiencies.
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Left side seems to be specialized for language from the very beginning in most people.
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The corpus callosum matures gradually through the first 5 to 10 years.
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Thus, young children have difficulty comparing information from the left and right hand.
Lateralization of Function
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Being born with a condition where the corpus callosum does not completely develop results in
extra development of the following:
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Anterior commissure - connects the anterior parts of the cerebral cortex.
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Hippocampal commissure - connects the left and right hippocampus.
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Allows performance on some tasks that differs from split-brain people.
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Lateralization of Function
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The left hemisphere is dominant for speech in 95% of right-handed people.
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Most left-handers have left-hemisphere or mixed-dominance for speech.
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Few people have strong right hemisphere dominance.
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Lateralization of Function
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Recovery of language after damage to the brain varies.
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Age affects extent of recovery.
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Brain is more plastic at an early age.
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Right hemisphere reorganizes to serve some of the left-hemisphere function.
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Lateralization of Function
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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.
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Usually begins in childhood or adolescence.
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Surgeons eventually remove or disconnect the side of the damaged brain.
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Language recovers slowly but substantially.
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Slow deterioration allows the other side of the brain to compensate and reorganize.
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Lateralization of Function
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Language recovery after brain damage is also influenced by how language was initially
lateralized for the given person.
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Individuals with partial representation of language in both hemispheres recover better than
those with language dominance in one hemisphere.
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Evolution and Physiology of Language
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Human language is a complex form of communication.
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Compared to other species, human language has high productivity/generativity.
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Productivity/generativity - the ability to produce new signals to represent new ideas.
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Evolution and Physiology of Language
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Human language is most likely a modification of a behavior also found in other species.
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Chimpanzees use language but it differs from humans:
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Seldom use symbols in new original combinations.
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Use of symbols lacks productivity.
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Use of symbols is primarily used to request and not describe.
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Production of requests is better than understanding other’s requests.
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Evolution and Physiology of Language
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Bonobos or pygmy chimpanzees show an increased comprehension of human language:
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Understand more than they can produce.
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Use symbols and names to describe objects.
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Request items not seen.
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Use symbols to describe past events.
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Make original, creative requests.
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Lateralization of Function
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Non-primates also display some aspects of spoken language.
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Elephants imitate sounds they hear, including the vocalizations of other elephants.
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Dolphins respond to gestures and sounds.
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The African gray parrot show a great ability for imitating sounds and also using sounds
meaningfully.
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Example: Alex the gray parrot.
Evolution and Physiology of Language
Studies of nonhuman language abilities:
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Give insights to how best to teach language to those who do not learn it easily.
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Examples: Brain damaged people or children with autism.
Illustrate the ambiguity of our concept of language.
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Allows for more precise definition.
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Evolution and Physiology of Language
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Two categories of theories attempt to explain the human ability to learn language more easily
than other species.
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“Language evolved as a by-product of overall brain development.”
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“Language evolved as an extra part of the brain.”
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Evolution and Physiology of Language
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Problems associated with the “language as a by-product of increased intelligence” theory:
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People with a full-size brain and normal overall intelligence can show severe language
deficits.
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People with impaired intelligence can have normal language skills.
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Williams syndrome characterized by metal retardation but skillful use of
language.
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Evolution and Physiology of Language
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Evidence suggesting language evolved as an extra brain module specialization includes:
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Language acquisition device is a built in mechanism for acquiring language.
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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.
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Evolution and Physiology of Language
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Most researchers agree that humans have a specially evolved “something” that enables them to
learn language easily.
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Certain brain areas are indeed necessary for language.
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But same areas are also necessary for other tasks (memory and music perception).
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Exactly how humans evolved language is unknown but is perhaps due to the pressure for social
interaction.
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Evolution and Physiology of Language
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Research suggests a critical period exists for the learning of language (Lenneberg).
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Learning of a second language differs as a function of age:
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Children are better at learning pronunciation and unfamiliar aspects of grammar.
No sharp cutoff exist for second language learning.
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Adults learn a second-language vocabulary better.
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Evolution and Physiology of Language
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Rare cases of children not exposed to language indicates limited ability to learn language later.
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Deaf children unable to learn spoken language and not given the opportunity to learn sign
language while young reveals:
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Little development of skill at any language later.
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Early exposure to some language increases ability to learn another language later.
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Evolution and Physiology of Language
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Most knowledge of brain mechanisms of language come from the study of people with brain
damage:
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Broca’s area is a part of the frontal lobe of the left cerebral cortex near the motor
cortex.
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Damage results in some language disability.
Aphasia refers to a condition in which there is severe language impairment.
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Evolution and Physiology of Language
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Broca’s aphasia/nonfluent aphasia refers to serious impairment in language production, usually
due to brain damage.
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Omission of most pronouns, prepositions, conjunctions, auxiliary verbs, tense and number
endings during speech production.
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People with Broca's aphasia have trouble understanding the same kinds of words they omit
(prepositions and conjunctions).
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Evolution and Physiology of Language
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Broca’s aphasia is usually accompanied by comprehension deficits when:
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The sentence meaning depends on prepositions, word endings or unusual word order.
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Sentence structure is complicated.
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Broca’s area thus seems to be critical for the understanding of some, but not all, aspects of
grammar.
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Evolution and Physiology of Language
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Wernicke’s area is an area of the brain located near the auditory part of the cerebral cortex.
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Wernicke’s aphasia is characterized by the impaired ability to remember the names of objects
and also impaired language comprehension.
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Sometimes called “fluent aphasia” because the person can still speak smoothly.
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Recognition of items is often not impaired; ability to find word is impaired.
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Evolution and Physiology of Language
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Typical characteristics of Wernicke’s aphasia include:
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Articulate speech / fluent speech except with pauses to find the right word.
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Difficulty finding the right word - anomia refers to the difficulty recalling the name of
objects.
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Poor language comprehension - difficulty understanding spoken and written speech
(especially nouns and verbs).
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Evolution and Physiology of Language
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Dyslexia is a specific impairment of reading in a person with adequate vision and adequate skills
in other academic areas.
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More common in boys.
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Research suggests a genetic influence.
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Evolution and Physiology of Language
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In some cases, dyslexia is associated with mild abnormality in the structures of various brain
areas.
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More likely to have a bilateral symmetrical cerebral cortex.
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Language–related areas in the right hemisphere are larger in some.
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Weak connections exist among other areas.
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Evolution and Physiology of Language
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Different kinds of dyslexics have different reading problems.
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“Dysphonic dyslexics” have trouble sounding out words.
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Attempt to remember them as a whole.
“Dyseidetic dyslexics” fail to recognize a word as a whole.
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Read slowly and have particular trouble with irregularly spelled words.
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Evolution and Physiology of Language
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Most severe cases of “dyseidetic dyslexia” result from brain damage that restricts the field of
vision.
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Characterized by the following:
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only seeing one letter a time.
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short eye movements.
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very slow reading.
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difficulty with long words.
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Evolution and Physiology of Language
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One hypothesis to explain dyslexia emphasizes a hearing impairment rather than visual
impairment.
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Less than normal response to speech sounds in the brain.
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Lack of ability to pay close attention to sounds.
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Evolution and Physiology of Language
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Another hypothesis to explain dyslexia is connecting vision to sound.
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Brain scans indicate that reading strongly activates areas of the left temporal and parietal cortex
for most people.
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Areas are associated with connecting visual and auditory information.
Only weakly activated for people with dyslexia.
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Evolution and Physiology of Language
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A final hypothesis relates dyslexia to differences in attention.
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Reading requires the shifting of attention.
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People with dyslexia do not shift their attention in the same way.
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Effective treatment may be for dyslexics to focus on one word at a time.
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Attention
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Attention is a multi-dimensional process and related to consciousness.
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Attention relates to increased brain activity in the areas responsive to a stimulus.
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Stimuli destined to become conscious or unconscious produce about the same brain activity in
the first 200-250 milliseconds.
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In the next few milliseconds, the brain enhances activity for stimuli that become conscious.
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Attention
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Enhancement of activity can be due to intensity of the stimulus, similarity to past important
stimuli, or other features of the stimulus itself.
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Enhancement of activity can also be due to shifting of attention.
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Research suggests that attention pertains more to the enhancing of relevant activity than
inhibiting irrelevant activity.
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Attention
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“Inattention” or “neglect” is the opposite of attention.
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Spatial neglect is a tendency to ignore the left side of the body and its surroundings or the left
side of objects.
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Often associated with damage to the right hemisphere of the brain.
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Attention
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Exact location of the damage to the right hemisphere can affect the details of what the person
neglects.
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Damage to the inferior part of the right parietal cortex leads to the neglect of everything
to the left of their own body.
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Damage to the superior temporal cortex neglect the left side of objects, regardless of
location.
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Attention
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Problems of neglect are associated with attention and not sensation.
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Someone with neglect can see an entire letter enough to say what it is.
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The same person ignores the left half when asked to cross out all the letters that compose a
word.
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Attention
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Several procedures can increase attention to the neglected side:
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telling the person to pay attention to the left side.
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telling the person to look left while feeling an object with the left hand or hearing a
sound from the left side.
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A touch stimulus briefly increases attention to one side of the body or the other.
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Crossing of the hands in front of the body also decreases neglect to the left side.
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Attention
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Many patients with spatial neglect also have deficits with spatial working memory and with
shifting attention, even when location is irrelevant.
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Thus, problems associated with neglect extend to many aspect of attention rather than simply
the left-right dimension.
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Attention
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Attention-Deficit Hyperactivity Disorder (ADHD) is characterized by the following:
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Attention deficits (distractibility).
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Hyperactivity (fidgetiness).
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Impulsiveness.
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Mood swings.
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Short temper.
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High sensitivity to stress.
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Impaired ability to make and follow plans.
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Attention
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ADHD affects social behavior and school performance.
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Some have occupational problems and antisocial behaviors in adulthood.
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Estimates range from 3%-10% of children
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Twice or three times as likely in males.
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Research is complicated by the ability to make reliable diagnoses.
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Attention
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Three example of tasks which people with ADHD differ:
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“The choice delay task” - more likely than others to choose a smaller but quicker reward
(impulsiveness).
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“The stop signal task” - difficulty inhibiting behaviors.
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“The attentional blink task” - indicates trouble controlling attention and difficulty
shifting it when needed.
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Attention
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Twin studies suggest fairly high heritability (Thapar et al., 2003).
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Several genes have been identified which influence performance on tests of attention.
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ADHD probably depends on multiple genes as well as environmental influences.
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Probability of ADHD is elevated among children of women who smoked cigarettes during
pregnancy.
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Attention
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Structural brain differences include a smaller than average prefrontal cortex and cerebellum.
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Cerebellar dysfunction is known to be associated with difficulty switching attention.
Structural differences in the brain are small and inconsistent between cases.
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Brain scans do not provide reliable results for diagnoses.
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Attention
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The most common treatment for ADHD is stimulant drugs or amphetamines.
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Example: methylphenidate/Ritalin.
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Stimulant drugs increase attentiveness, improve school performance and social relationships,
and decrease impulsiveness.
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Also improve scores on laboratory tests, such as the “stop signal task”.
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Justifying the benefits derived from taking the drugs is a complex and controversial issue.
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Attention
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Amphetamines and methylphenidate increase the availability of dopamine to the postsynaptic
receptors.
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Maximum benefit occurs 1 hour after ingestion and benefits last for a few hours.
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Several studies have found that stimulant drugs enhance certain aspects of learning and
attention for all people, not just those with ADHD.
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Attention
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Behavioral techniques are available as supplements or substitutes for stimulant drugs:
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Reduce distractions.
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Use lists, calendars, and other organizational techniques.
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Practice strategies to pace yourself.
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Learn to relax; tension and stress can magnify attention deficits.