Localisation of Function

Motor Cortex

Motor Cortex

Controls voluntary movement

Broca’s area

Responsible for the production of speech

Auditory cortex

Processes information from our ears

Wernicke’s area

Responsible for the understanding of language

Visual cortex

Processes information from our eyes

Somatosensory cortex

Processes information about touch, pain, temperature, and proprioception

Hemispheric lateralisation of function

Different functions are dominant in each hemisphere

Corpus callosum

Connects the two brain hemispheres

What is found in the left hemisphere?

Broca’s and Wernick’s areas

What is the left hemisphere responsible for?

Logic, analysis and problem-solving

What is the right hemisphere responsible for?

Spatial comprehension, emotions and face recognition

How do the two hemispheres communicate?

1. Information from the right visual field (that’s the right half of what you see) goes to the visual cortex in the left hemisphere

2. Information from the left visual field goes to the visual cortex in the right hemisphere

3. Information passes through the corpus callosum to whichever side of the brain needs to deal with it

Split brain surgery

Severs the corpus callosum to treat severe epilepsy

What method did Sperry use when investigating the effects of split-brain surgery on brain functions?

• The study involved a combination of case studies and experiments

• The 11 participants had undergone split-brain surgery as a result of epilepsy that couldn’t be controlled by medication

• A control group had no hemisphere disconnection

• In one of the experiments, participants covered one eye and looked at a fixed point on a projection screen

• Pictures were projected onto the left or right of the screen at high speeds so that there was no time for eye movement

What were the results of Sperry’s study?

• If the picture was shown in the right visual field, all of the participants could say or write what it was without a problem

• But if the image flashed onto the left the split-brain participants couldn’t say or write down what they’d seen

• They could however select a corresponding object with their left hand, which represented what had been shown to their left eye (right hemisphere), even though they didn’t know why they had selected this object

What was the conclusion of Sperry’s study?

• This shows that different areas of the brain specialise in different functions

• The left hemisphere (which receives visual information from the right visual field) can convert sight into spoken and written language

• Usually, information entering the right hemisphere can cross over to be processed in the left.

• As the results show, this can’t happen in split brains, so the information going to the right hemisphere can’t be converted into language at all

• However, the right hemisphere can still produce a non-verbal response

What was the evaluation of Sperry’s study?

• Using case studies as well as experiments meant that Sperry obtained both qualitative and quantitative data

• Using both research methods meant that the reliability and the validity of the study were increased

• The study only used 11 participants, which is a very small sample size for being able to generalise the results to others

• It would have been difficult to find a large number of split-brain patients to study

• Epilepsy is usually caused by brain damage and the patients had also been on medication which may have affected their brains

• It is hard to conclude that the ways they processed information would be the same as for people without epilepsy or split-brain treatment

• The study has also been criticised in terms of ecological validity- the experimental situation was artificial, so it’s difficult to generalise the results to real-life situations