split-brain research into hemispheric lateralisation

Question 1

What is hemispheric lateralisation?

Answer 1

that the two hemispheres of the brain are functionally different

Question 2

What split-brain research did Roger Sperry (1968) do?

Answer 2

He conducted experiments on epileptic patients who had a surgical separation called commissurotomy (corpus callosum is cut). They did this to control seizures as communication between the 2 hemispheres is removed.

Question 3

What procedure did Sperry use?

Answer 3

The participants were asked to focus on a spot of light in which an image/word is projected to either visual field briefly.

In a normal brain, the corpus callosum would share the information between the hemispheres, whereas in a split brain, the information can’t be conveyed.

Question 4

Sperry’s findings - what you see

Answer 4

• picture shown to the right visual field split-brain patients could describe what they saw
• same picture shown to the left visual field they couldn’t describe what they saw

This is as language is processed in the left hemisphere since these aren’t on the right hemisphere messages can’t be conveyed in split brain patients.

Question 5

Sperry’s findings - recognition by touch

Answer 5

• split-brain patients could select objects from a bag using their left-hand
• objects were behind a screen and the left hand could select an object which was mostly associated with the object in the left visual field

They couldn’t verbally say what they had seen but understood what the object was using the right hemisphere and selected a corresponding object

Question 6

Jerry’s findings - recognition by touch

Answer 6

• split-brain patients could select objects from a bag using their left-hand
• the objects were behind a screen and the left hand could select an object mostly associated with the object in the left visual field

They couldn’t verbally say what they had seen but understood what the object was using the right hemisphere and selected the corresponding object

Question 7

Sperry’s findings - composite words

Answer 7

• two words were simultaneous, one on the left visual field and one on the right visual field, the patient would write the word on the left using their left hand and say the word on the right

This highlights how the right hemisphere is better at drawing tasks

Question 8

Jerry’s findings - matching face

Answer 8

• when asked to match a face from a series of faces, the picture in the left visual field was consistently selected
• The picture in the right visual field was ignored

when a composite picture made up of 2 different halves of a face is presented, 1/2 of each hemisphere, the left hemisphere was better at verbal descriptions.

Question 9

How is research support for lateralisation a strength?

Answer 9

Michael Gazzaniga (1989) - PPTs who had split-brain performed better than connected controls on tasks.
- faster at identifying the odd object
- in normal brains, the left hemisphere’s better cognitive strategies are ‘watered down’ by the interior right hemisphere

Question 10

How is one brain a weakness of lateralisation?

Answer 10

The idea that the left hemisphere is an analyser and the right hemisphere is a synthesiser may be wrong.

The 2 hemispheres may have different functions
- research suggests that people don’t have a dominant side which creates personality

Question 11

What research is a weakness of the one-brain argument?

Answer 11

Nielson et al (2013) - analysed brain scans of people aged 7-29 over 1000 people
- people used certain hemispheres for certain tasks
- no dominant side.

Question 12

How are problems of generalisation a weakness of lateralisation?

Answer 12

• the control group was made up of people with no history of epilepsy
  
  • confounding variable as any difference between groups may have been due to having epilepsy and not split-brain
• only 11 patients in the experimental group took part
• Some PPTs experience more disconnection of the surgery

makes results difficult to generalise

Question 13

How is good methodology a strength of lateralisation?

Answer 13

• highly specialised & standardised procedures
  
  • methods used described as ‘indigenous’ due to high levels of control

Due to its scientific nature, it is more reliable

Question 14

How is theoretical debate a strength of lateralisation?

Answer 14

• Sperry’s work prompted a debate about the degree of communication in the hemispheres
• some (Puccetti 1977) = 2 hemispheres are so different
  
  • represents the duality of the brain = 2 minds hemispheres form a highly integrated system and both involved in tasks

This prompted researchers to debate communication between 2 sides of the brain