Chapter 14: Lateralization & Language
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Chapter 14: Lateralization & Language

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

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

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Chapter 14: Lateralization & Language Chapter 14: Lateralization & Language Presentation Transcript

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