Lesson 7 - Hemispheric Lateralisation & Split Brain Research

Question 1

Hemispheric Lateralisation

Answer 1

Refers to the notion that certain functions are principally governed by one side of the brain

Question 2

Hemispheric Lateralisation

Systematic Research

Answer 2

Demonstrates most language areas are in left
Broca’s Area thought to be responsible for speech production but now it is thought to involve a wider network
Damage to Broca’s Area leads to expressive aphasia
Wernicke’s Area is vital in understanding language
Damage to Wernicke’s Area leads to receptive aphasia
Right hemisphere dominant for visuo-spatial functions

Question 3

Brain Hemispheres

Answer 3

Right hemisphere is responsible for left hand side of body
Left hemisphere is responsible for right hand side of body
If a patient is experiencing right sided paralysis, there is lateralised damage to left hemisphere
Two hemispheres connected by a bundle of nerve fibres known as corpus callosum which enables communication
Two hemispheres work together to form most tasks

Question 4

Hemispheric Lateralisation Evaluation Points

Answer 4

Rogers et al. (2004) - Evolutionary Perspective
Szaflarski et al. (2006) - Age
Global Aphasia
Turk et al. (2002) - JW
Danelli et al. (2013) - EB

Question 5

Hemispheric Lateralisation Evaluation
Rogers et al. (2004) - Evolutionary Perspective
Positive

Answer 5

Hemispheric lateralisation makes sense from an evolutionary perspective
Increases neural processing capacity, which is adaptive
By using one hemisphere to engage in a task, it leaves the other to engage in another task
Rogers et al. (2004) found hemispheric lateralisation in chicks is associated with an ability to multi task

Question 6

Hemispheric Lateralisation Evaluation
Szaflarski et al. (2006) - Age
Negative

Answer 6

Lateralisation pattern shifts with age with most tasks becoming less lateralised in healthy adulthood

Question 7

Hemispheric Lateralisation Evaluation
Global Aphasia
Positive

Answer 7

Patients who have extensive damage to their left hemisphere can experience global aphasia
(Loss of speech production and speech comprehension)
This suggests that language is lateralised to the left hemisphere

Question 8

Hemispheric Lateralisation Evaluation
Turk et al. (2002) - JW
Negative

Answer 8

JW (a split brain patient) developed the capacity to speak using his right hemisphere, with the result that they cold speak about information presented in either the left visual field or right visual field hemisphere
It would appear that language is not lateralised entirely to the left hemisphere

Question 9

Hemispheric Lateralisation Evaluation
Danelli et al. (2013) - EB
Negative

Answer 9

If one hemisphere is damaged, undamaged regions on the opposite can compensate
EB had virtually his entire left hemisphere removed
Language appeared almost normal in everyday life in terms of vocabulary and grammar
However, systematic testing revealed subtle grammatical problems as well as poorer normal scores on picture naming and reading of loan words
Language function can be largely preserved after removal of left hemisphere but right, by itself, cannot provide a perfect mastery of each component of language

Question 10

Split Brain Research

Answer 10

Surgeons have cut the corpus callosum in order to prevent the violent electrical activity caused by epileptic seizures crossing from one hemisphere to the other
Patients who underwent this form of surgery are often referred to as split brain patients
Sperry and Gazzaniga (1968)

Question 11

Split Brain Research

Sperry and Gazzaniga (1968)

Answer 11

Investigated split brain patients
Information from left visual field goes into right hemisphere, vice versa
In split brain patients, the corpus callosum has been severed there is no way for the information presented to one hemisphere to travel to the other

Question 12

Split Brain Research
Sperry and Gazzaniga (1968)
Method

Answer 12

Patients asked to stare at a dot in the centre of a screen
Information is presented in either left or right visual field
Asked to make response with their left hand (right hemisphere), right hand (left hemisphere) or verbally (left hemisphere) without being able to see what their hands were doing

Question 13

Split Brain Research
Sperry and Gazzaniga (1968)
Findings

Answer 13

May be flashed image of dog in right visual field then asked what they have seen
Answer dog due to information going to left hemisphere, where language centres are
If picture of cat is shown in left visual field and they asked what they seen, they are unable to answer because information has gone to right hemisphere which has no language centres
However, they can draw a picture of a cat with their left hand because the right hemisphere controls this hand

Question 14

Split Brain Research Evaluation Points

Answer 14

Discoveries
Scientific
Drug Therapy
Generalisation
Ecological Validity

Question 15

Split Brain Research Evaluation
Discoveries
Positive

Answer 15

Split brain research has enabled discoveries of hemispheric lateralisation

Question 16

Split Brain Research Evaluation
Scientific
Positive

Answer 16

Experiments on split brain patients are highly controlled and scientific

Question 17

Split Brain Research Evaluation
Drug Therapy
Negative

Answer 17

Pateients often had drug therapy for their epilepsy for much longer than others
May affect brain processing
Means findings cannot be generalised to target population

Question 18

Split Brain Research Evaluation
Generalisation
Negative

Answer 18

Many studies using split brain patients have as a few as three patients
Makes it hard for results to be generalised to target population

Question 19

Split Brain Research Evaluation
Ecological Validity
Negative

Answer 19

Data from research is artificial
In the real world, a severed corpus callosum can be compensated for by the unrestricted use of both visual fields
Means research lacks ecological validity