Hemispheric lateralisation and split-brain research

Question 1

What is hemispheric lateralisation?

Answer 1

The 2 halves of the brain are functionally different, and certain mental processes are controlled mainly by one hemisphere

Question 2

What is split-brain research?

Answer 2

Studies involving people with epilepsy who experienced a surgical separation of the brain’s hemispheres to reduce the severity of their epilepsy

Question 3

How is language lateralised?

Answer 3

• Performed by one hemipshere (left)
• RH only produces rudimentary words/phrases but contributes but contributes emotional context

Question 4

What are some examples of functions that are not lateralised?

Answer 4

• Vision
• Motor area
• Somatosensory area

Question 5

What is the role of the RH and LH?

Answer 5

RH= synthesiser
LH= analyser

Question 6

What occurs in the motor area?

Answer 6

• The brain is cross-wired (contralateral wiring)
• RH controls movement on the left side
• LH controls movement on the right side

Question 7

What is vision classed as?

Answer 7

• Contralateral (cross-wired)
• Ipsilateral (opposite, same sided)

Question 8

How is light received?

Answer 8

• Received from left visual field AND right visual field
• LVF is connected to RH
• RVF is connected to LH
• Visual areas compare the different perspectives from each eye- aids depth of perception

Question 9

Strength:
I- Lateralisation in the connected brain

Lateralisation

Answer 9

D- Fink et al used PET scans to identify which areas of the brain are active during a visual processing task. Connected brain participants attended to global elements of an image, and the RH was active
E- Suggests hemispheric lateralisation is a feature of both the connected and split brain

Question 10

Limitation
I- One brain/pop-psychology

Lateralisation

Answer 10

D- RH as synthesiser and LH as analyser may be incorrect. Research suggets there is not a dominant side of the brain. Nisan et al analysed brain scans of 1000+ people aged 7-29. Found people used certain hemispheres for specific tasks but there was no evidence of a dominant side
E- Supports idea that right/left brained people is wrong

Question 11

Evaluation extra- Lateralisation vs plasticity

Lateralisation

Answer 11

Strength: Lateralisation provides an adaptive function. Rogers showed that chickens with lateralised brains could find food, whilst looking for predators. Chickens reared in the dark, with non-lateralised brains could not do this. Lateralsiation is the 1st preference

Limitation: Neural plasticity seen as adaptive. After trauma/damage, non-specialised areas take over functions. Holland- language ‘switches sides’. Lateralised functions are flexible not fixed

Question 12

What do split-brain operations do?

Answer 12

• (Commisurotomy)
• Sever the connections between LH and RH (corpus callosum)
• Procedure to reduce epilepsy

Question 13

What does the right hemisphere do?

Answer 13

• No language
• Has understanding
• Facial recognition
• Synthesiser (whole picture)

Question 13

What does the left hemisphere do?

Answer 13

• Language
• Analyser (details of picture)

Question 14

What did Sperry study?

Answer 14

• Studied how 2 hemispheres deal with speech and vision

Question 15

What was Sperry’s procedure?

Answer 15

• 11 split-brain patients (commissurotomy) were studied
• Stare at fixation point on screen
• Image/word was flashed on screen for 1/10 of a second
• Participants asked to say/draw what they saw

Question 16

What did Sperry find?

Answer 16

• When image shown to RVF, patient could describe what they saw
• Image shown to LVF, could not describe
• Participants couldn’t give verbal labels to LVF objects but could select matching object using left hand
• When pinup picture was shown to LVF, emotional reaction (giggle) but claim they saw nothing

Question 17

What did Sperry conclude?

Answer 17

• Certain functions are lateralised in the brain
• Supports the view that LH is verbal (analyser) and RH is silent but emotional (synthesiser)

Question 18

Strength:
I- Research support

Split-brain research

Answer 18

D- Gazzaniga- split brain patients perform better than control on certain tasks. E.g: faster at identifying the odd one out than control group. Kingstone- In normal brain, LH’s cognitive strategies are watered down by RH
E- Supports Sperry’s findings that left and right brain differ

Question 19

Limitation:
I- Generalisation issues

Split-brain research

Answer 19

D- Hard to establish causal relationships. Split-brain patients (Sperry) were compared to neurotypical group.Differences may be result of epilepsy not split-brain
E- Means some unique features of split-brain patients’ cognitive abilities have been due to some epilepsy

Question 20

Strength:
I- Highly reliable

Split brain research

Answer 20

D- Images/words were flashed up for 1/10 of a second, preventing participants’ eyes moving. This allows the image/word to go to one hemipshere only
E- Means research is highly standardised and can be reliably replicated

Question 21

I- Ethical issues

Evaluation extra

Answer 21

• Harm was not deliberate- participants had already had their corpus callosum cut out
• Trauma of operation meant patients did not understand implications of what they agreed to (stress, strain of testing)