Chapter 14: Lateralization & Language


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The brain and language, the evolution of language, brain damage and language.

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Chapter 14: Lateralization & Language

  1. 1. Lateralization & Language
  2. 2. Lateralization of Function <ul><li>Contralateral Control </li></ul><ul><li>Corpus Callosum </li></ul><ul><li>Set of axons which allow the 2 hemispheres to exchange information </li></ul><ul><li>Cutting the corpus callosum prevents sharing of this information </li></ul><ul><li>Some are born without a corpus callosum </li></ul><ul><li>Lateralization </li></ul><ul><li>Each hemisphere specializes in certain behavior & cognitive abilities </li></ul><ul><li>E.g., language is mainly in the left hemisphere </li></ul>
  3. 3. Lateralization of Function <ul><li>Visual Input </li></ul><ul><li>Light from the right visual field shines onto the left half of both retinas </li></ul><ul><li>This is relayed to the left hemisphere </li></ul><ul><li>The right half of each retina connects to the right hemisphere which sees the left visual field </li></ul>
  4. 4. Lateralization of Function <ul><li>Split-brain Responses </li></ul><ul><li>With a severed corpus callosum can point to objects with the left hand, but not the right </li></ul><ul><li>With visual information presented to the right visual field can name or describe what is seen </li></ul><ul><li>Right hemisphere: is better than the left at perceiving emotions in gestures & tone of voice </li></ul><ul><li>With right hemisphere damage can speak with less inflection & expression </li></ul><ul><li>Right is more adept at compre-hending spatial relationships </li></ul><ul><li>Also better at perceiving patterns instead of details </li></ul>
  5. 5. Lateralization of Function <ul><li>Planum Temporale </li></ul><ul><li>A section of the temporal cortex larger in the left hemisphere in 65% of the population </li></ul><ul><li>The difference in size is apparent at 3 months </li></ul><ul><li>Children with the biggest ration of left to right planum temporale are better on language tests </li></ul>
  6. 6. Lateralization of Function <ul><li>Corpus Callosum </li></ul><ul><li>Slowly develops over the first 5 to 10 years </li></ul><ul><li>Neurons connected to the corpus callosum take years to develop their mature adult pattern </li></ul><ul><li>Those born without a corpus callosum seem to have larger than normal hemispheric connections elsewhere </li></ul><ul><li>Anterior Commisure </li></ul><ul><li>Connects the hemispheres around the anterior parts of the cerebral cortex </li></ul><ul><li>The hippocampal commisure connects the left hippocampus to the right hippocampus </li></ul>
  7. 7. Lateralization of Function <ul><li>Speech & Hemispheric Dominance </li></ul><ul><li>90% of people are right handed & left hemisphere dominance for speech </li></ul><ul><li>Others are either right hemisphere dominant or mixed </li></ul><ul><li>Corpus callosum is larger in left handers than right handers </li></ul><ul><li>Recovery from Injury </li></ul><ul><li>Recovery of speech after brain injury depends on the damaged hemisphere & how speech is lateralized </li></ul><ul><li>Children with left-hemisphere damage recover more language than adults with similar damage, but the cause of the damage is more important with age </li></ul>
  8. 8. Human Language <ul><li>Uniqueness </li></ul><ul><li>Productivity creates uniqueness </li></ul><ul><li>Ability to produce new signals to represent new ideas </li></ul><ul><li>Chimp Communications </li></ul><ul><li>Cannot learn to talk but can learn some language skills using ASL or other visual systems </li></ul><ul><li>Use of language-related skills differ from human language </li></ul><ul><li>Bonobo Communications </li></ul><ul><li>Uses symbols in several ways that more resemble humans </li></ul><ul><li>Use of language-related skills similar in several ways </li></ul>
  9. 9. Evolution of Human Language <ul><li>A Product of Overall Intelligence </li></ul><ul><li>Brain-to-body ratio relationship can’t explain language </li></ul><ul><li>Is it a dominant gene? </li></ul><ul><li>Language development is unclear </li></ul><ul><li>Special Module </li></ul><ul><li>Language Acquisition Device </li></ul><ul><li>Language evolved as an extra brain module </li></ul><ul><li>Language has a critical period ; if language isn’t learned during childhood development it leads to disadvantages </li></ul>
  10. 10. Brain Damage & Language <ul><li>Aphasia </li></ul><ul><li>Severe language impairment </li></ul><ul><li>Broca’s Area </li></ul><ul><li>Small part of the left frontal cortex when damaged leads to language impairments </li></ul><ul><li>Wernicke’s Area </li></ul><ul><li>Near the auditory part of the left temporal lobe </li></ul>
  11. 11. Brain Damage & Language <ul><li>Broca’s Aphasia </li></ul><ul><li>Nonfluent aphasia </li></ul><ul><li>Most prominent symptom: deficit in language production </li></ul><ul><li>Damage to Broca’s area </li></ul><ul><li>Can speak meaningfully but omits pronouns, prepositions, conjunctions & qualifiers </li></ul><ul><li>Some trouble understanding the same kinds of words </li></ul>
  12. 12. Brain Damage & Language <ul><li>Wernicke’s Aphasia </li></ul><ul><li>Fluent aphasia </li></ul><ul><li>Difficulty in understanding verbal & written communications, can speak smoothly but speech is often nonsensical </li></ul><ul><li>Anomia: difficulty recalling the names of objects </li></ul><ul><li>Language Activation </li></ul><ul><li>Language requires activation of many different areas of the frontal & temporal cortex </li></ul>
  13. 13. Dyslexia <ul><li>Inability to Read Properly </li></ul><ul><li>Has adequate intelligence & vision </li></ul><ul><li>Many underlying causes </li></ul><ul><li>Bilateral Symmetrical Cerebral Cortex </li></ul><ul><li>Have left & right hemisphere structures the same size </li></ul><ul><li>Hypotheses </li></ul><ul><li>Unresponsive magnocellular path to the visual system </li></ul><ul><li>A subtle hearing impairment </li></ul><ul><li>Problem converting vision to sound & vice-versa </li></ul><ul><li>Function of attentional differences </li></ul><ul><li>Problem communicating between hemispheres </li></ul>