Split Brain Research Into Hemispheric Lateralisation

Question 1

What is hemispheric lateralisation?

Answer 1

The idea that the two halves (hemispheres) of the brain are functionally different and that certain mental processes and behaviours are mainly controlled by one hemisphere rather than the other- most stimuli is processed contralaterally

Question 2

What is split-brain research?

Answer 2

A series of studies which began in the 1960s (and are still ongoing) involving epileptic patients who had experienced a surgical separation of the hemispheres of the brain. This allowed researchers to investigate the extent to which brain function is lateralised (as hemisphere cannot communicate with each other)

Question 3

What’s an example of hemispheric lateralisation?

Answer 3

The ability to reproduce and understand language for most people is controlled by the left hemisphere

Question 4

Explain how and why split-brain studies involve a unique group of individuals

Answer 4

Sperry’s (1968) studies involved participants who had undergone the same procedure- a commisurotomy where the corpus callosum which connect the two hemispheres can no longer communicate with each other so they act like two separate brains = allowed Sperry to see the extent to which the two hemispheres were specialised for certain functions, and the extent to which the hemispheres performed tasks independently of one another

Question 5

What was the aim of Sperry and Gazzaniga (1968) natural experiment?

Answer 5

To investigate whether functions are lateralised

Question 6

What were the participants and sampling method for Sperry and Gazzaniga’s natural experiment (1968)?

Answer 6

11 male ‘split-brain’ participants through opportunity sampling

Question 7

What was procedure 1 (visual stimulus) of Sperry and Gazaniga’s natural experiment? (1968)?

Answer 7

• one eye covered
• asked to stare at central dot on a screen
• words or images flashed to one or both sides of the screen
• participants asked to write, draw or say what they’ve seen

Question 8

What were the results of procedure 1 (Sperry and Gazzaniga)?

Answer 8

• participants unable to recall word or identify image if presented to their left visual field (right hemisphere) but were able to if image presented to their right visual field (left hemisphere)- participants’ inability to describe objects in the left visual field (processed by the right hemisphere) is because of the lack of language centres (Broca’s and Wernicke’s area in the right hemisphere in most people
• participants can draw what they saw if presented to their left visual field but only with their left hand
• participants only remember seeing the image/word if shown it to the same hemisphere again

Question 9

What was procedure 2 (tactile stimulus) of Sperry and Gazaniga’s natural experiment? (1968)?

Answer 9

• objects presented to the right or left hand of the participant behind a screen
• participant asked to identify, feel, point to or draw objects with each hand

Question 10

What were the results of procedure 1 (Sperry and Gazzaniga)?

Answer 10

• objects placed in right hand can describe the object in speech or writing (because left hemisphere needed for this)
• objects placed in left hand, participants made a wild guess
• when an object is placed in one hand, they can later point to it with the same hand

Question 11

What was procedure 3 (composite words and matching faces) of Sperry and Gazaniga’s natural experiment? (1968)?

Answer 11

• two words were presented simultaneously, one on either side of the visual field e.g. if ‘key’ was presented to the left and ‘ring’ to the right, the participant would select a key with their left hand (left hand goes to right hemisphere linked to left visual field) and say the word ‘ring’ (right visual field linked to key hemisphere)
• right hemisphere appears dominant in terms of matching faces. When asked to match a fave from a series of other faces, the picture processed by the right hemisphere (left visual field) was consistently selected. When a composite picture made up of two different halves of a face was presented (one half to each hemisphere) the left hemisphere dominated in terms of verbal description whereas the right hemisphere dominated in terms of selecting a matching picture

Question 12

What were the conclusions made from Sperry and Gazaniga’s natural experiment? (1968)

Answer 12

• left hemisphere specialises in speech/language production

- right hemisphere specialises in facial recognition

Question 13

What are the evaluation points for split-brain research?

Answer 13

✅ demonstrated lateralised brain functions
✅ strengths in methodology Sperry used
✅ Sperry’s work prompted a theoretical debate about the nature of the brain
❌ low external validity (generalisations) in relation to Sperry’s work

Question 14

Explain how a strength of split-brain research is that it demonstrated lateralised functions

Answer 14

The main conclusions of Sperry’s split -brain research are that the left hemisphere is more dominant regarding speech (production) ,‘ the analyser’, whilst the right hemisphere is more dominant with performing spatial tasks and facial recognition, ‘the synthesiser’, thus showing lateralised brain functions.

ALTHOUGH, more recent research has suggested that even this distinction may be oversimplified and that several tasks associated with one hemisphere can also be carried out by the other- Gazzaniga (1998) suggested that some of the early discoveries from split-brain research have been disconfirmed by more recent discoveries. For example, split-brain research had suggested that the right hemisphere was unable to handle even the most rudimentary language. Damage to the left hemisphere was found to be far more detrimental to language function than was damage to the right. However case studies have demonstrated that this was not necessarily the case- one patient known as J.W. developed the capacity to speak out of the right hemisphere, with the result that J.W. can now speak about information presented to the left or the right brain

Question 15

Explain how there were strengths in the methodology Sperry used

Answer 15

The tasks involving split-brain patients mad use of highly specialised and standardised procedures. Sperry’s method of presenting visual information to one hemispheric field at a time was quite ingenious. Patients were asked to stare at a fixed point, whilst one eye was blindfolded; the image projected would be flashed up for 1/10th of a second, meaning the patient would not have time to move their eye across the image and spread the information across both sides of the visual field, and subsequently, both sides of the brain. This allowed Sperry to vary aspects of this basic procedere and ensure that only one hemisphere was receiving information at a time. Thus he developed a very useful and well-controlled procedure

Question 16

Explain how Sperry’s work prompted a theoretical debate about the nature of the brain

Answer 16

Sherry’s work triggered a a theoretical and philosophical debate about the nature of consciousness and the degree of communication between the two hemispheres in everyday functioning. Pucetti suggested that the hemispheres are so functionally different that they represent a form of ‘duality’ in the brain (that in effect we are two minds). In contrast, other researchers have argued that the two hemispheres are a highly integrated system and work together during most tasks e.g. complex of learning. As a result, the value of Sperry’s work is in this on-going debate and enabled further investigation to occur into the extent of hemispheric lateralisation .

Question 17

Explain how a limitation of Sperry’s work is its generalisability

Answer 17

As fascinating as split-brain studies are, many researchers have said they cannot widely be accepted as split-brain patients are zsuch an unusual sample of people. There were only 11 patients who partook in all variations of the basic procedure, all of whom had a history of epileptic seizures. It has been argued that this may caused unique changes in their brains that may have influenced the findings a possible extraneous variable in the natural study. Consequently, this limits the extent to which findings can be generalised to ‘normal’ brains reducing the external validity of Sperry’s findings