What lateralisation of function means

1. Your brain is divided into two halves called hemispheres, a left one and a right one.
2. Asymmetrical function means the two hemispheres are not mirror images of each other in what they do, because each one takes the lead on different tasks.
3. Each hemisphere deals mainly with the opposite side of the body, so the right hemisphere controls the left side of the body and the left hemisphere controls the right.
4. You will see this crossed-over arrangement called contralateral control. The label is handy shorthand, but it is the plain version of the idea that earns the mark.

The role of the left hemisphere

1. In most people the left hemisphere leads on language, which covers speaking, reading and writing.
2. It also leads on step by step, logical and analytical tasks such as working through a calculation.
3. It controls movement and sensation on the right side of your body.

The role of the right hemisphere

1. The right hemisphere leads on spatial tasks, such as judging where objects sit in relation to each other or arranging blocks into a pattern.
2. It also leads on recognising faces and on picking up emotion from a face or a scene.
3. Its language ability is limited, so it can read and understand some simple words but usually cannot produce speech.
4. It controls movement and sensation on the left side of your body.

The role of the corpus callosum

1. The corpus callosum is a thick band of nerve fibres running between the two hemispheres.
2. It carries messages across, so information arriving at one hemisphere can reach the other.
3. This is why lateralisation does not leave you with two separate minds, because whatever the right hemisphere takes in can be passed to the left hemisphere and put into words.

The evidence from split-brain patients

1. Sperry (1968) studied 11 patients whose corpus callosum had been cut to treat severe epilepsy, which meant each hemisphere could be tested on its own.
2. When the word KEY was shown to the left visual field and CASE to the right, patients said and wrote 'case' and denied seeing anything on the left, yet their left hand still picked out the key correctly.
3. That pattern is strong evidence that language is lateralised to the left hemisphere, because the right hemisphere clearly took the word in but could not say it.

Lateralisation as an explanation of sex differences

1. Lateralisation has been used to try to explain average differences between males and females on tasks such as language and spatial reasoning.
2. The claim is that male brains are more strongly lateralised, with a task handled mainly by one hemisphere, while females appear to show less lateralisation for language abilities and more activity across both hemispheres.
3. Strength: there is evidence supporting it, because scans taken while people do language tasks tend to show activity spread across both hemispheres more often in females, and women more often keep some language after damage to the left hemisphere, which is what the explanation predicts.
4. Strength: it starts from something well evidenced, since Sperry (1968) shows lateralisation itself is real, and it makes clear predictions that other researchers can try to repeat.
5. Weakness: there is also evidence refuting it, because larger studies find the overlap between males and females is far bigger than any gap between them, and the difference often fails to appear when the work is repeated.
6. Weakness: it is reductionist, because it puts a difference down to brain structure alone and ignores nurture, such as the different experiences, expectations and amounts of practice people are given.

Turning this into marks

1. Name Sperry (1968) with the conclusion it supports attached, because a study named on its own only reads as description.
2. Quote the detail that patients said 'case' while their left hand still picked out the key.
3. The mark most often lost is the second side of the argument, so give a strength and a weakness whenever you are asked to weigh lateralisation up.