Chapter Fourteen Lateralization and Language

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Chapter FourteenLateralization and Language
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
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Lateralization of Brain Function
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
2 of 30

• Two hemispheres are not mirror images of each
  other
• left hemisphere controls right side of body
• right controls left side
• taste and smell input to same side
• Lateralization is the specialization of labor
  between the two hemispheres
• left hemisphere specialized for language
• right specialized for complex visual-spatial
  tasks and synthetic processing

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Commissures
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
3 of 30

• Commissures where axons connect hemispheres and
  exchange information
• corpus callosum is the primary information
  highway between hemispheres
• without CC, left hemisphere could only talk about
  information from right side of body and right
  hemisphere could only react to information from
  left side of body
• also includes the anterior and hippocampal
  commissures

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Figure 14.1
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
4 of 30

• Figure 14.1 Two views of the corpus callosum. The
  corpus callosum is a large set of axons conveying
  information between the two hemispheres. (a) A
  sagittal section through the human brain. (b) A
  dissection (viewed from above) in which gray
  matter has been removed to expose the corpus
  callosum.

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Figure 14.4
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
5 of 30

• Figure 14.4 The anterior commissure and
  hippocampal commissures. These commissures allow
  for the exchange of information between the two
  hemispheres, as does the larger corpus callosum.
  (Source Based on Nieuwenhuys, Voogd,
  vanHuijzen, 1988, and others.)

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Visual and Auditory Connections to the Hemispheres
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
6 of 30

• Visual field what is visible at any moment
• both eyes see both left and right visual fields
• right visual field goes to left half of both
  retinas, through optic chiasm to left hemisphere
  
• left visual field goes to right half of both
  retinas, through optic chiasm to right hemisphere
• center of both retinas, covering 5º arc of visual
  field, connects to both hemispheres
• Auditory each ear receives sound waves from just
  one side of head but each sends information to
  both sides of the brain

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Figure 14.2
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
7 of 30

• Figure 14.2 Connections from the eyes to the
  human brain. (a) Route of visual input to the two
  hemispheres of the brain. Note that the left
  hemisphere is connected to the left half of each
  retina and thus gets visual input from the right
  half of the world the opposite is true of the
  right hemisphere. (b) Closeup of olfactory bulbs
  and the optic chiasm, where axons from the right
  half of the left retina cross to the right
  hemisphere, and axons for the left half of the
  right retina cross to the left hemisphere.

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Split Brain Behavior
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
8 of 30

• Cutting the corpus callosum prevents exchange of
  information between two hemisphere
• sometimes cut as therapy for severe epilepsy
• seizures only affect half of body and are less
  frequent
• Creates split-brain behavior
• e.g. if lab animals see something in left field,
  they can only respond with left forepaw
• person has difficulty learning any new task that
  requires both hands but can use hands
  independently easier than normal people

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Split Brain Behavior cont.
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
9 of 30

• Person viewing objects in only one side of the
  visual field can point to them only with opposite
  hand
• Left hemisphere is dominant for speech
  comprehension and speech production in 95 of
  right handers and 80 of left
• left responds to meaningful language (including
  sign language if fluent)
• can name object in right visual field but usually
  not in left
• both hemispheres respond equally to nonlanguage
  sounds or to languages not spoken

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Split Brain Behavior cont.
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
10 of 30

• Words hot and dog were shown in left and right
  visual fields but could not be combined into
  hotdog
• left hand drew overheated dog
• After surgery cutting CC, competition between
  hemispheres diminish
• e.g. left hemisphere knew that guess about name
  of object on left visual field was wrong when
  right hemisphere made face frown
• All but the simplest tasks require cooperation by
  both hemispheres

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Right Hemisphere
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
11 of 30

• Recognizes gestures, emotional expressions and
  tone of voice better than left side
• with left hemisphere damage could detect liars on
  video
• happier face had smile in left visual field
• activated by fear and anger

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Right Hemisphere cont.
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
12 of 30

• When damaged, person speaks in monotone, doesnt
  understand emotional expression, humor or sarcasm
  
• Better at spatial processing and pattern
  recognition
• woman with damage had trouble finding way about
  town
• split brain persons better using left hand to
  arrange puzzle pieces and draw
• large H activates right hemisphere

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Anatomical Differences between the Hemispheres
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
13 of 30

• Left hemisphere specialized for language from
  birth
• plenum temporale larger in 65 of all people and
  in 12 of 14 infants who died within 3 months
• children with biggest left-right ratio performed
  best on language tests
• damage to left hemisphere results in less
  language than same damage to right

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Development Without a Corpus Callosum
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
14 of 30

• Corpus Callosum takes 5-10 years to determine
  which axons will interconnect between hemispheres
  and survive
• People born without CC can do tasks that adult
  with cut CC cant, e.g., can describe object held
  in either hand and what they see in either visual
  field
• they have developed pathways to both sides of
  body and other commissures become larger

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Handedness and Language Dominance
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
15 of 30

• Right handedness a heritage
• 10 of people are left-handed or ambidextrous
• 90 of prehistoric drawings show tools in right
  hand
• most chimps and other primates are right handed
• Left handers
• have equal as well as left or right hemisphere
  dominance for speech
• if right is dominant, left hemisphere contributes
  more to spatial perception
• CC is thicker for greater communication

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Recovery of Speech After Brain Damage
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
16 of 30

• Suppressing activity in the hemisphere dominant
  for speech, also blocks speech
• but not when person has bilateral control of
  speech
• Recovery from brain damage
• person will recover substantially from damage to
  either left or right hemisphere, with bilateral
  speech control
• with left or right dominance person will recover
  best when opposite hemisphere is damaged
• left hemisphere damage usually requires increased
  activity in surviving areas

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Recovery of Speech After Brain Damage cont.
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
17 of 30

• Two year old can lose entire left hemisphere and
  still develop language in right hemisphere
• but, age less important than problem that caused
  damage
• children more than 10 years old with Rasmussens
  encephalopathy recover some speech after removal
  of left hemisphere

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Evolution and Physiology of Language
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
18 of 30

• Human language is different because it is more
  productive
• can produce new signals to represent new ideas
• Chimpanzees can learn to communicate using sign
  language or symbols, but different from human
  language
• symbols used to request but rarely to describe
• seldom recombine in new combinations
• say more than they understand, the opposite of
  children

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Evolution and Physiology of Language cont.
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
19 of 30

• But, bonobo chimp Kanzi learned up to 150 words
  and demonstrated language ability of 2 - 2 1/2
  year old child
• may have more potential than other chimps, or due
  to observation and imitation, or began when young
• Studies with non-humans
• dolphins can learn to respond to commands
• gray parrot, can count and name objects and their
  color
• may help teach language to others, e.g., brain
  damaged people or autistic children
• suggests human language evolved from
  reorganization of brain circuits

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Language as a Product of Intelligence
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
20 of 30

• We evolved big brains and great intelligence
  therefore language developed as a by-product
• but elephant and whale brains are bigger
• Brain-to-body ratio
• humans are high but squirrel monkey and elephant
  nosed fish and chihuahua have higher ratios
• Also, research on brain size and intelligence is
  mixed some found a correlation, and some found
  no relationship

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Language as a Product of Intelligence cont.
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
21 of 30

• People with undamaged, full-sized brains can
  still have impaired language
• genetic condition impaired 16 of 30 in family
• People with Williams syndrome are retarded in
  many ways but language less impaired
• much like adults who learn second language

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Language as a Special Module
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
22 of 30

• Humans have evolved with something that enables
  them to learn language easily
• Chomsky and Pinker a language acquisition device
• children learn language with ease, including
  children of deaf parents
• deaf children learn sign or invent one of their
  own
• partly genetic, e.g., mutation of FOXP2 on
  chromosome 7 found in 16 of 30 family members
  with impairments
• not likely a separate module since most language
  areas used for other functions, e.g., memory,
  music perception
• intelligence may be by-product of language

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Critical Periods for Language Development
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
23 of 30

• Children learn the pronunciation and unfamiliar
  aspects of language better than adults
• adults are better at memorizing vocabulary
• The earlier you start learning a second language
  the better
• but the amount of language area in brain
  activated depends on mastery, not age started
• The earlier the child has a chance to learn sign
  language, the more skilled they will become
• If you do not learn language before starting
  school, you will never develop much skill

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Brocas Aphasia
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
24 of 30

• Also called non-fluent aphasia
• severe deficits in language production caused by
  damage to Brocas area, and other cortical and
  subcortical structures
• difficulty pronouncing, gesturing and writing as
  well as understanding complex speech
• uses and understands nouns and verbs more easily
  than closed-class words, e.g., prepositions,
  pronouns
• ignores grammar and relies on inferences
• but, can usually recognize when something is
  wrong with sentence even if they cannot correct it

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Wernickes Aphasia
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
25 of 30

• Also called fluent aphasia
• caused by damage to left temporal cortex
• seriously impaired language comprehension
• difficulty finding the right word and trouble
  recalling names of objects
• grammatical but often nonsensical speech
• perhaps because cant find words due to rapid
  speech
• but, can pronounce clearly, fluently and rapidly

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Figure 14.15
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
26 of 30

• Figure 14.15  Some major language areas of the
  cerebral cortex. In most people only the left
  hemisphere is specialized for language.

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Structure and Function of Brocas and Wernickes
Areas
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
27 of 30

• Frontal lobe around Brocas area is linked to
  procedural memory
• critical for regular past tenses, e.g., add -ed
  to verbs
• Temporal lobe, including Wernickes area is
  linked to declarative memory
• critical for names of objects and irregular past
  tense verbs, e.g., hit, drove, kept
• But, these functions are inferred with caution
• English language requires more procedural
  checking than, say, Italian and activates more of
  brain, so functions may vary

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Dyslexia
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
28 of 30

• Specific impairment of reading with adequate
  vision and adequate skills in other academic
  areas
• More common in boys than girls
• Has genetic basis and different types of dyslexia
  may have different genetic bases
• More common among English readers, partly due to
  odd words, e.g., phlegm, bivouac, khaki
• Reading can be improved by exposing one word at a
  time
• did not need special cut-out in 3 weeks
• lost ability to attend to several tasks at once

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Dyslexia Hypotheses
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
29 of 30

• May be due to relatively unresponsive
  magnocellular paths in the visual system,
  impairing perception of motion patterns
• May be due to hearing impairment
• prevents hearing difference between similar words
  
• difficulty tapping fingers rapidly to rhythms

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Dyslexia Hypotheses cont.
James W. Kalat
Biological Psychology, 8th Edition
Chapter 14 Lateralization and Language
30 of 30

• May be due to difficulty converting sound to
  vision
• weak connections among several brain areas,
  unlike normal readers
• can report visual differences between two
  nonsense words but have trouble reporting
  differences between visual and auditory
  presentations
• May be due to difference in attention
• More interference from adjacent letters than for
  letters 5-10º away, which contributes to reading
  difficulties