Lang, Lateralisation + Split Brain
- Created by: brobs123
- Created on: 17-05-17 13:22
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- Lang, Lateralisation + Split Brain
- Lateralisation
- Early Evidence
- Marc Dax (1836)
- Noticed patients with speech issues had damage to right hemisphere of brain
- Broca (mid 1800's)
- Aphasia: inability to produce or understand lang
- Marc Dax (1836)
- Testing it
- Dichotic listening (more remembered in dominant ear)
- Sodium Amytal
- Knocks out half of brain
- Beyond Lang
- 95% right handed = left hemisphere dominant for speech
- 70% left handed/ambi = left hemisphere dominant for speech
- Broca's Area
- Inferior Left Prefrontal Lobe in LH
- Damage leads to Broca's Aphasia (most common cause = stroke)
- Wernicke's area
- Left Temporal Lobe, posterior to primary auditory cortex
- Damage leads to deficits in semantic lang comprehension (speech is incomprehensible)
- Can understand speech but cannot speak
- Early Evidence
- Split brain
- Myers and Sperry (1953)
- 4 goups of cats (severed corpus collosum/severed optic chiasm/both severed/both intact)
- 2 Conditions
- 1 = learned lever press pattern discrimination task with patch over 1 eye (all 4 groups readily learned)
- 2 = switched eye patch (groups 1,2,4 had same results but 3 acted as if new task)
- 2 Conditions
- 4 goups of cats (severed corpus collosum/severed optic chiasm/both severed/both intact)
- First efforts to split brain in 40's on life-threatening epilepsy patients (was very effective)
- Tests on split-brain patients
- Visual stimuli flashed on either right/left of fixation point on a screen
- Tactual info presented to 1 hand under table/in bag
- Objects presented to right hemisphere
- Picked out correct object with left but not right
- Claimed nothing had been presented
- Picked out correct object with left but not right
- Objects presented to left hemisphere
- Picked out correct object with right hand but not left
- Could name correct object
- Picked out correct object with right hand but not left
- Cross-cuing
- Communication but not within brain
- E.g. patient claimed verbally that red had flashed on screen but head shook and he changed answer
- Right hemisphere heard incorrect guess of left and shook head to signal it was wrong
- Capable of learning 2 things at once
- Helping hand phenomena (right changes lefts hand to correct object)
- E.g. patient claimed verbally that red had flashed on screen but head shook and he changed answer
- Communication but not within brain
- Myers and Sperry (1953)
- Difference between right + left hemisphere
- Right
- Levy 1969
- Right better at spatial tasks
- Kimura 1964
- Better at tasks involving emotional stimuli and music
- Memory: Attends to perceptual characteristics of stimuli
- Holistic
- Heschl's Gyrus larger in RH
- Levy 1969
- Left
- Broca + Aphasia
- Left prefrontal lobe
- Leipmann
- More activity in left hem during lang-related activites
- Memory: Places experience in wider context (relation of parts that make whole)
- Analytical
- Planum Temporale larger in LH
- Broca + Aphasia
- Right
- Language
- Analytic-Synthetic Theory
- 2 fundamentally different modes of thinking (analytic = LH, Synthetic = RH)
- Neural circuitry for each is fundamentally different
- LH (pieces of the whole) = Logical, sequential, analytical
- RH (the whole) = immediate, overall synthetic judgements
- Popular as reinforces stereotypes but vague
- Motor Theory
- LH specialised in fine motor skills (e.g. speech)
- Lesions of LH disrupt facial movements more than RH lesions even if not related to speech
- Degree of disruption of NV facial movements = + correlated with degree of aphasia
- Linguistic theory
- Primary function of LH is lang
- Based on studies of deaf people who commun through SL
- Ability for SL lost if damage to LH even if they're able to make movements required
- Analytic-Synthetic Theory
- Evolution
- Survival adv of lateralisation
- 5 classes of vertebrates= all have lateralized brains
- efficient to locate similar neurons that do the same thing
- better to have one highly skilled hand rather than two moderately skilled ones
- Some tasks easier to perform lateralised
- Communication in other species
- Lang specialised skill unique to humans
- Slocombe and Zuberbuhler 2007
- Primates = repertoire of sounds have specific meaning others understand
- Motor theory consistent with mirror neuron theory b/c of fine movements while speaking
- Activation when listening agrees with motor patterns
- Survival adv of lateralisation
- Lateralisation
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