Hemispheric lateralisation | AQA A-Level Psychology Revision
- Revision Notes
- Aug 3
- 22 min read
Updated: Aug 23
For 7182 specification, first teach in September 2025
AQA A-Level Psychology | Free Revision Notes
Estimated study time: 50 minutes
These Hemispheric lateralisation A-Level Psychology revision notes explain how some functions are mainly controlled by one side of the brain. You will examine the role of the corpus callosum and explore how split-brain research investigated the abilities of the left and right hemispheres separately. The topic develops your understanding of specialised areas within the cerebral cortex and prepares you to consider how the hemispheres may adapt following damage in changes to brain organisation.
Learning Objectives 🎯
By the end of this revision page, you should be able to:
Define hemispheric lateralisation.
Distinguish hemispheric lateralisation from localisation of function.
Explain the role of the corpus callosum.
Describe the procedure used in split-brain research.
Explain the main findings of split-brain research.
Apply visual-field and hand information to unfamiliar scenarios.
Evaluate research into hemispheric lateralisation.
Revision Notes 📚
Hemispheric lateralisation A-Level Psychology revision overview
The brain is divided into two cerebral hemispheres:
The left hemisphere.
The right hemisphere.
The hemispheres appear similar in their overall structure, but they are not completely identical in their functions.
Hemispheric lateralisation is the principle that some physical and psychological functions are mainly controlled or processed by one cerebral hemisphere rather than being shared equally between both.
For example:
Language is usually more strongly associated with the left hemisphere.
Some visuospatial and face-processing abilities are more strongly associated with the right hemisphere.
Each hemisphere mainly controls movement on the opposite side of the body.
Each hemisphere mainly receives visual information from the opposite visual field.
The hemispheres normally work together, exchanging information through the corpus callosum.
The two cerebral hemispheres
The cerebral hemispheres are the two halves of the brain.
Hemisphere | Side of the brain |
Left hemisphere | Left side |
Right hemisphere | Right side |
Each hemisphere contains areas associated with:
Movement.
Bodily sensation.
Vision.
Hearing.
Language and communication.
Higher cognitive processing.
Some functions are represented in both hemispheres, while others are more strongly lateralised.
Lateralisation does not mean that one hemisphere performs all of a function entirely by itself.
What does lateralisation mean?
A function is lateralised when one hemisphere makes a greater contribution to it than the other.
For example, language production is usually described as left-lateralised because Broca’s area is normally located in the left hemisphere.
However, language also involves:
Auditory processing.
Memory.
Attention.
Emotional tone.
Motor control.
Communication between several brain areas.
A function can therefore be lateralised without being produced by one isolated hemisphere.
Lateralisation and localisation are different
Localisation of function concerns particular areas within the brain.
Hemispheric lateralisation concerns differences between the two cerebral hemispheres.
Localisation of function | Hemispheric lateralisation |
Particular areas perform particular functions | Some functions are more strongly associated with one hemisphere |
Focuses on specific brain regions | Focuses on differences between the left and right hemispheres |
Example: the visual centre is in the occipital lobe | Example: language is usually left-lateralised |
Can occur within either hemisphere | Involves hemispheric specialisation |
Broca’s area illustrates both concepts:
It is localised in a particular area of the frontal lobe.
It is usually lateralised to the left hemisphere.
The relationship between named brain centres and their functions is covered in motor, sensory and language centres.
Contralateral control
Many pathways in the brain are contralateral.
This means that one hemisphere primarily controls or processes information from the opposite side.
For movement:
The left hemisphere mainly controls the right side of the body.
The right hemisphere mainly controls the left side of the body.
Hemisphere | Main side of body controlled |
Left hemisphere | Right side |
Right hemisphere | Left side |
Damage to the motor centre in the left hemisphere may therefore affect voluntary movement on the right side of the body.
Contralateral sensory processing
Bodily sensory information is also mainly processed contralaterally.
Sensory information from the right side of the body is mainly processed in the left hemisphere.
Sensory information from the left side of the body is mainly processed in the right hemisphere.
This arrangement becomes especially important in split-brain research because researchers can present information to one hand or one visual field.
Visual fields and hemispheres
Visual information is divided according to the visual field, not simply according to the eye receiving it.
The visual fields are:
The left visual field.
The right visual field.
Information from the visual fields is processed contralaterally:
Visual field | Hemisphere receiving the information |
Right visual field | Left hemisphere |
Left visual field | Right hemisphere |
Information from the right visual field is received by both eyes but is transmitted primarily to the left hemisphere.
Information from the left visual field is also received by both eyes but is transmitted primarily to the right hemisphere.
⚠️ It is therefore inaccurate to say:
The right eye sends all information to the left hemisphere.
The left eye sends all information to the right hemisphere.
The important distinction concerns the visual field, not the eye.
Example of visual-field processing
Imagine a participant focuses on a dot in the centre of a screen.
The word BOOK appears briefly to the participant’s right.
Because the word appears in the right visual field:
The visual information travels primarily to the left hemisphere.
The left hemisphere processes the word.
The participant is likely to be able to say what they saw because language production is usually left-lateralised.
Now imagine that the word appears to the participant’s left.
Because it appears in the left visual field:
The information travels primarily to the right hemisphere.
A split-brain participant may process the visual information.
They may be unable to say the word because the information cannot reach the language centres in the left hemisphere.
The corpus callosum
The corpus callosum is a thick bundle of nerve fibres connecting the left and right cerebral hemispheres.
Its function is to allow information to pass between them.
In an intact brain, the hemispheres share information rapidly.
For example:
An image appears in the left visual field.
The information reaches the right hemisphere.
The corpus callosum transfers relevant information to the left hemisphere.
Language areas in the left hemisphere help the person describe what they saw.
This communication usually makes the two hemispheres appear to operate as one coordinated system.
The role of interhemispheric communication
Communication through the corpus callosum allows the hemispheres to combine their specialised abilities.
For example, answering a question about an image may involve:
Visual processing.
Recognition.
Memory.
Language comprehension.
Speech production.
Motor control.
Some of these processes may be more strongly associated with one hemisphere, but successful performance depends on communication between both.
Hemispheric specialisation therefore does not mean that the hemispheres normally work independently.
Split-brain surgery
Some people with severe epilepsy underwent an operation in which the corpus callosum was cut.
This procedure is known as a commissurotomy or corpus callosotomy.
The purpose was to prevent epileptic activity from spreading between the hemispheres.
After the operation:
The left hemisphere continued to function.
The right hemisphere continued to function.
Communication between them was greatly reduced.
Information presented to one hemisphere could not transfer normally to the other.
People who had undergone this operation became known as split-brain patients.
What is split-brain research?
Split-brain research investigates people whose corpus callosum has been severed.
The research examines what happens when information is presented to only one hemisphere.
This allows psychologists to study the abilities of each hemisphere more independently than would usually be possible.
The best-known research was conducted by Roger Sperry and colleagues.
Sperry investigated how split-brain participants responded when visual or tactile information was directed to one hemisphere.
Participants in Sperry’s research
Sperry studied a small group of people who had undergone split-brain surgery as a treatment for severe epilepsy.
The participants differed from typical members of the population because they:
Had experienced epilepsy.
Had undergone major brain surgery.
May have taken medication.
Had reduced communication between the hemispheres.
Could differ in the amount of neural tissue severed.
These characteristics are important when evaluating whether the findings generalise to people with intact brains.
The purpose of Sperry’s research
Sperry aimed to investigate the specialised abilities of the two hemispheres.
In a typical brain, information can pass through the corpus callosum, making it difficult to determine which hemisphere first processed it.
In split-brain participants, information presented to one hemisphere remains largely within that hemisphere.
Researchers could therefore test questions such as:
Can the left hemisphere recognise an object?
Can the right hemisphere understand a simple word?
Can the participant say what was shown to the right hemisphere?
Can one hand select an object that the participant cannot verbally name?
Controlling visual presentation
To direct visual information to one hemisphere, the participant focused on a central point on a screen.
A word, picture or object was then presented very briefly to one side.
The presentation needed to be brief because eye movements could allow the information to enter both visual fields.
Presentation position | Hemisphere receiving the information |
Right of fixation point | Left hemisphere |
Left of fixation point | Right hemisphere |
By controlling where the stimulus appeared, researchers could control which hemisphere received it first.
Why participants had to fixate
The participant was instructed to keep their eyes focused on a point in the centre of the screen.
This was necessary because:
Moving the eyes changes the visual field.
A longer presentation would allow the participant to look directly at the image.
The information might then reach both hemispheres.
Researchers would no longer know which hemisphere had processed it.
The procedure therefore depended on rapid presentation and careful control of eye movement.
Testing the left hemisphere
To send information to the left hemisphere, a stimulus was presented in the participant’s right visual field.
For example:
The participant focused on the centre of a screen.
The word KEY appeared briefly in the right visual field.
The information travelled to the left hemisphere.
The participant was asked what they had seen.
The participant could usually say “key”.
This supports the conclusion that the left hemisphere is normally dominant for language production.
Testing the right hemisphere
To send information to the right hemisphere, a stimulus was presented in the left visual field.
For example:
The participant focused on the centre of a screen.
The word KEY appeared briefly in the left visual field.
The information travelled to the right hemisphere.
The participant was asked what they had seen.
The participant was usually unable to name the word verbally.
They might report that they saw nothing.
This did not necessarily mean that the right hemisphere had failed to process the stimulus. It meant that the information could not transfer to the left hemisphere’s language-production systems.
Selecting an object with the left hand
Although the participant could not verbally name an item shown to the right hemisphere, they might be able to select the correct object with their left hand.
This occurs because:
The left visual field sends information to the right hemisphere.
The right hemisphere controls the left hand.
The right hemisphere can guide the left hand towards the matching object.
The information does not need to transfer to the left hemisphere for verbal identification.
For example:
The word “spoon” is shown in the left visual field. The participant says they did not see a word but uses their left hand to select a spoon from several hidden objects.
This demonstrates that the right hemisphere processed the information even though the participant could not report it verbally.
Why the right hand may select incorrectly
The right hand is mainly controlled by the left hemisphere.
If a stimulus is shown only to the right hemisphere:
The right hemisphere processes it.
The left hemisphere does not receive the information.
The right hand is controlled by the uninformed left hemisphere.
The participant may be unable to select the correct object using the right hand.
The split between verbal and manual performance provides evidence that the hemispheres have different abilities.
Tactile tasks
Sperry also used tactile tasks, involving the sense of touch.
An object could be placed in one hand while hidden from view.
Because each hand is mainly controlled and processed by the opposite hemisphere:
Hand receiving the object | Hemisphere receiving most tactile information |
Right hand | Left hemisphere |
Left hand | Right hemisphere |
If an object was placed in the right hand, the left hemisphere received the information and the participant could usually name it.
If the object was placed in the left hand:
The right hemisphere received the tactile information.
The participant might be unable to name the object.
They could still recognise it non-verbally.
They might select or use the object appropriately with the left hand.
Drawing tasks
Split-brain participants could sometimes draw an object shown to the right hemisphere using the left hand.
For example:
A picture was presented in the left visual field.
The information reached the right hemisphere.
The participant could not verbally name it.
The left hand could draw or select the object.
This suggests that the right hemisphere can guide visuospatial responses without relying on verbal language.
Composite-image tasks
Researchers could also present different images to the two visual fields.
For example:
One half of a face might be shown to the left visual field.
A different half might be shown to the right visual field.
When asked to describe what they saw verbally, participants tended to report information received by the left hemisphere.
When asked to select a matching face non-verbally, the right hemisphere’s information could have a stronger influence.
Such findings supported the view that the hemispheres differ in their relative strengths.
Main findings of split-brain research
Sperry’s research produced several important findings.
Finding 1: Language is usually left-lateralised
Participants could normally name words and objects presented to the right visual field because the information reached the left hemisphere.
They were usually unable to name information presented only to the right hemisphere.
This supports the view that speech and language production are mainly controlled by the left hemisphere.
Finding 2: The right hemisphere can process information without verbal reporting
A participant might say they saw nothing but still select the correct object with the left hand.
This showed that failure to verbalise did not mean failure to process.
The right hemisphere could:
Recognise some visual information.
Guide a manual response.
Complete some visuospatial tasks.
Process information independently of speech production.
Finding 3: The hemispheres have specialised abilities
The results suggested that:
The left hemisphere is generally more specialised for language.
The right hemisphere is generally stronger in visuospatial and some face-processing tasks.
However, these are relative differences rather than absolute divisions.
Finding 4: The hemispheres normally operate together
The unusual responses occurred because communication through the corpus callosum had been disrupted.
In people with an intact corpus callosum:
Information can pass between the hemispheres.
The left hemisphere can verbally describe information first processed on the right.
The specialised abilities of both hemispheres are integrated.
Summary of Sperry’s visual-field findings
Stimulus presentation | Hemisphere receiving it | Likely verbal response | Likely hand response |
Right visual field | Left hemisphere | Can usually name the item | Right hand can usually select it |
Left visual field | Right hemisphere | Usually cannot name the item | Left hand can usually select it |
This table applies to a split-brain participant under controlled conditions.
It does not describe the ordinary performance of someone whose corpus callosum is intact.
Applying visual-field information
Consider this situation:
A split-brain participant sees a picture of a cup briefly presented in the left visual field.
The likely sequence is:
The picture is transmitted primarily to the right hemisphere.
The corpus callosum cannot transfer the information normally.
Language-production areas in the left hemisphere do not receive it.
The participant is unlikely to say “cup”.
The right hemisphere controls the left hand.
The participant may select a cup using the left hand.
Applying right visual-field information
Now consider:
The word “pencil” is presented briefly in the right visual field.
The likely sequence is:
The word reaches the left hemisphere.
The left hemisphere includes the main language centres.
The participant can usually say “pencil”.
The left hemisphere controls the right hand.
The participant can usually select the pencil using the right hand.
Applying tactile information
Consider this scenario:
A split-brain participant closes their eyes. A coin is placed in their left hand.
The likely outcome is:
Tactile information is transmitted mainly to the right hemisphere.
The participant may be unable to say that the object is a coin.
They may be able to identify or use it correctly with the left hand.
The right hemisphere has processed the object’s shape and texture.
The information cannot transfer normally to language areas in the left hemisphere.
A method for answering split-brain application questions
Use the following steps.
1. Identify the visual field or hand
Was the stimulus presented to:
The left visual field?
The right visual field?
The left hand?
The right hand?
2. Identify the receiving hemisphere
Use the contralateral rule.
Input | Hemisphere |
Left visual field | Right hemisphere |
Right visual field | Left hemisphere |
Left hand | Right hemisphere |
Right hand | Left hemisphere |
3. Identify the required response
Is the participant being asked to:
Speak?
Point?
Draw?
Select an object?
Use the left or right hand?
4. Identify the hemisphere controlling the response
Speech production is usually controlled by the left hemisphere.
The left hand is mainly controlled by the right hemisphere.
The right hand is mainly controlled by the left hemisphere.
5. Consider the severed corpus callosum
Ask whether the hemisphere receiving the information can share it with the hemisphere producing the response.
Worked application example
A split-brain participant is shown the word “apple” in the left visual field and is asked to say what they saw.
A developed explanation would state:
The word is presented in the left visual field.
It is therefore transmitted primarily to the right hemisphere.
Language production is normally lateralised to the left hemisphere.
The severed corpus callosum prevents the information transferring normally to the left hemisphere.
The participant is therefore unlikely to say “apple”.
They may still be able to select an apple using the left hand because the right hemisphere controls that hand.
Strength: controlled procedures
One strength of Sperry’s research was the high level of control.
Researchers controlled:
Where the stimulus appeared.
How long it was visible.
Where the participant looked.
Which hand completed the task.
What response was required.
The type of material presented.
This allowed the researchers to isolate input to one hemisphere.
A standardised procedure also made it possible to repeat tasks across participants and conditions.
This supports the reliability of the findings.
Strength: objective measurements
Responses in split-brain research were often clear and observable.
Researchers could record whether a participant:
Named a word correctly.
Selected the matching object.
Drew the presented item.
Used the correct hand.
Recognised a face.
Reported seeing nothing.
These responses were less dependent on subjective interpretation than an unstructured description of experience.
Objective behavioural measures support psychology’s use of scientific methods.
Strength: consistent patterns
Despite differences among split-brain participants, several patterns appeared repeatedly.
For example:
Information presented to the left hemisphere could usually be named.
Information presented to the right hemisphere could not normally be verbally reported.
The left hand could identify objects processed by the right hemisphere.
The right hemisphere showed strengths in some visuospatial tasks.
Repeated patterns increase confidence that the findings reflect meaningful hemispheric differences.
Strength: support for lateralisation
Split-brain research provides direct evidence that the hemispheres have specialised functions.
When communication was disrupted:
The left hemisphere showed stronger verbal abilities.
The right hemisphere could guide non-verbal responses.
Information available to one hemisphere was not always available to the other.
This would be difficult to observe in people with intact corpus callosums because information normally transfers between the hemispheres.
Strength: practical understanding of the brain
Research into hemispheric lateralisation has contributed to understanding:
The organisation of language.
The role of the corpus callosum.
Contralateral control.
The integration of specialised functions.
The possible effects of brain surgery or injury.
This knowledge may contribute to the assessment and support of people with neurological damage.
Limitation: small and unusual sample
Sperry’s research used a small group of split-brain patients.
These participants were unusual because they:
Had severe epilepsy.
Had undergone major brain surgery.
May have received long-term medication.
Had different medical histories.
Could differ in the extent of their disconnection.
The findings may not generalise fully to:
People without epilepsy.
People with intact corpus callosums.
The wider population.
The sample provided rare and valuable evidence, but it was not representative.
Limitation: individual differences
Not every split-brain participant produced exactly the same result.
Differences may have resulted from:
The extent of the surgery.
The age at which surgery occurred.
The length of time since the operation.
Previous experience.
Recovery and neural adaptation.
The severity of epilepsy.
Differences in language lateralisation.
A general conclusion about “the split brain” may overlook variation between individuals.
Limitation: epilepsy as a confounding variable
The participants had experienced severe epilepsy before the operation.
Epilepsy itself may affect:
Brain structure.
Brain functioning.
Cognitive performance.
Attention.
Memory.
Language.
Medication used to manage epilepsy may also influence performance.
It is therefore difficult to know whether every difference resulted solely from severing the corpus callosum.
Limitation: no random allocation
Participants could not be randomly assigned to have their corpus callosum cut.
The research involved a naturally occurring difference between people who had undergone the operation and those who had not.
This means:
Participant variables were not fully controlled.
The research was not a conventional laboratory experiment.
Causal conclusions require caution.
Differences may have existed before surgery.
The design allowed detailed investigation but could not provide complete experimental control.
Limitation: artificial tasks
The tasks used in split-brain research were highly artificial.
Participants might have been asked to:
Stare at a fixation point.
View an image for a fraction of a second.
Identify objects hidden from view.
Respond with only one hand.
Process unrelated words or pictures.
These tasks differ from everyday life, where:
People move their eyes freely.
Stimuli remain visible for longer.
Both hemispheres usually receive information.
People use several senses together.
Behaviour occurs in a meaningful context.
The research may therefore have limited ecological validity.
Why everyday effects may be less noticeable
Split-brain patients often functioned relatively normally in everyday life.
This may be because:
Everyday information is available for longer.
People can move their eyes.
Both hemispheres can receive the same information.
Other communication pathways may remain.
Participants can use environmental clues.
Practice may help them adapt.
The dramatic separation seen in controlled tasks may therefore exaggerate the difference experienced in ordinary situations.
Limitation: repeated testing
Split-brain participants often completed many research tasks.
Repeated testing could allow them to:
Learn what researchers expected.
Develop strategies.
Anticipate stimuli.
Compensate for difficulties.
Practise particular responses.
Performance may therefore reflect both hemispheric organisation and experience with the procedure.
Limitation: oversimplifying the hemispheres
Split-brain findings are sometimes reduced to simple claims such as:
The left hemisphere is logical.
The right hemisphere is creative.
People are either left-brained or right-brained.
These claims oversimplify the research.
Complex activities usually involve:
Both hemispheres.
Several localised regions.
Communication through neural networks.
Learning and experience.
Interaction between cognitive processes.
A person should not be classified as a “left-brained” or “right-brained” personality based on split-brain findings.
Relative rather than absolute specialisation
A function being lateralised does not mean the other hemisphere makes no contribution.
For example:
Language is usually left-lateralised.
The right hemisphere may contribute to emotional tone, context and other aspects of communication.
Visuospatial processing is often associated with the right hemisphere.
The left hemisphere may still contribute to many spatial tasks.
It is more accurate to describe relative dominance than total exclusivity.
Limitation: conclusions about intact brains
Split-brain research investigates brains in which the usual communication pathway has been deliberately disrupted.
The behaviour of these participants may not show exactly how an intact brain ordinarily operates.
In an intact brain:
Information transfers between hemispheres.
Functions are coordinated.
Performance reflects integrated processing.
One hemisphere may compensate for or support the other.
Split-brain research reveals what each hemisphere can do under separation, but this may differ from its role within a connected system.
Lateralisation and plasticity
The brain can adapt following experience or damage.
After split-brain surgery:
Participants may develop compensatory strategies.
Other neural connections may support some communication.
Practice may improve task performance.
Functions may reorganise to some extent.
This means performance may change over time.
The brain should not be viewed as permanently fixed immediately after surgery.
The capacity for change is considered in experience, damage and neural reorganisation.
Lateralisation and functional recovery
If a hemisphere or specialised area is damaged, other brain regions may sometimes support recovery.
This could involve:
Homologous areas in the opposite hemisphere.
Reorganisation of nearby tissue.
Development of new neural pathways.
Increased use of existing connections.
This does not remove evidence for lateralisation. It suggests that lateralised functions can sometimes become more widely distributed following damage.
These processes are examined further in recovery following brain trauma.
Evidence from fMRI
Functional magnetic resonance imaging can contribute to research into lateralisation.
Researchers can compare activity in the left and right hemispheres while participants complete tasks.
For example, an fMRI study may investigate whether:
Language produces greater activity in the left hemisphere.
Face processing produces greater activity in the right hemisphere.
Both hemispheres contribute to a complex task.
A major advantage is that fMRI studies the living, connected brain.
However:
It measures blood-oxygenation changes indirectly.
Activity does not prove exclusive responsibility.
High activity in one hemisphere does not mean the other is inactive.
The method is reviewed in blood oxygenation and functional brain maps.
Evidence from EEGs and ERPs
EEGs and ERPs can investigate when the hemispheres respond to stimuli.
Researchers may place electrodes across both sides of the scalp and compare electrical activity following an event.
This provides:
High temporal resolution.
Evidence about the timing of hemispheric responses.
Information from the living brain.
However, EEGs and ERPs have relatively poor spatial resolution, so the precise source of activity may be difficult to identify.
The techniques are covered in electrical brain activity and event-related responses.
Evidence from post-mortem examinations
Post-mortem examinations may identify damage in one hemisphere and connect it with behaviour recorded during life.
For example, damage to language areas in the left hemisphere may be associated with aphasia.
This can support lateralisation, but:
The brain cannot be observed functioning.
Damage may affect several regions.
The relationship is often correlational.
Information about earlier behaviour may be incomplete.
The strengths and limitations of this evidence are explained in structural examination of the brain after death.
Combining different sources of evidence
Evidence for hemispheric lateralisation comes from several methods:
Method | Contribution |
Split-brain research | Tests hemispheric abilities after communication is disrupted |
fMRI | Compares activity in the hemispheres during tasks |
EEGs and ERPs | Measures the timing of electrical responses |
Post-mortem examinations | Connects structural damage with behaviour during life |
Brain-damage cases | Shows possible effects of damage to one hemisphere |
Agreement across several methods strengthens the conclusion that some functions are lateralised.
However, each method has different limitations, so evidence should be interpreted together.
Writing an effective description of split-brain research
A strong answer might state:
Sperry investigated participants whose corpus callosum had been severed to treat epilepsy. Participants focused on a central point while words or images were presented briefly to one visual field. Information shown in the right visual field travelled to the left hemisphere and could usually be named. Information shown in the left visual field travelled to the right hemisphere and could not normally be named, although participants could select the matching object with their left hand. The findings support left-hemisphere dominance for language and right-hemisphere strengths in non-verbal and visuospatial processing.
This answer:
Identifies the participants.
Explains the corpus callosum.
Describes visual presentation.
Applies contralateral processing.
Gives key findings.
Links findings to hemispheric functions.
Writing an effective evaluation paragraph
A developed evaluation paragraph might state:
One strength of Sperry’s research was the use of highly controlled procedures. Stimuli were presented briefly to one visual field while participants maintained central fixation, allowing researchers to direct information to one hemisphere. This made the findings easier to replicate and supported conclusions about hemispheric specialisation. However, the tasks were artificial because people do not normally view isolated stimuli for fractions of a second while keeping their eyes fixed. The findings may therefore exaggerate the independence of the hemispheres in everyday life.
This paragraph:
Identifies a methodological strength.
Explains why it matters.
Introduces a connected limitation.
Explains its effect on validity.
Overall conclusions from split-brain research
Split-brain research suggests that:
The hemispheres have specialised functions.
Language is usually left-lateralised.
The right hemisphere can process information that cannot be verbally reported.
The right hemisphere shows strengths in some visuospatial tasks.
Each hemisphere mainly controls the opposite hand.
Each hemisphere mainly receives information from the opposite visual field.
The corpus callosum normally integrates information.
The hemispheres are specialised but not completely independent.
The most accurate conclusion is not that people have two separate minds.
Instead, the research shows that the hemispheres make different contributions and normally combine these through interhemispheric communication.
Key Words 🔑
Key word | Student-friendly definition | How it may be used in an exam |
Hemispheric lateralisation | The principle that some functions are more strongly associated with one cerebral hemisphere. | Define the topic or explain differences between the hemispheres. |
Cerebral hemisphere | One of the two main halves of the brain. | Identify where lateralised functions are located. |
Left hemisphere | The left half of the brain, usually dominant for language. | Explain verbal responses in split-brain tasks. |
Right hemisphere | The right half of the brain, associated with some non-verbal and visuospatial abilities. | Explain manual or visuospatial responses. |
Corpus callosum | A bundle of nerve fibres connecting the two hemispheres. | Explain how information normally passes between hemispheres. |
Split-brain patient | A person whose corpus callosum has been surgically severed. | Identify the participants used in Sperry’s research. |
Commissurotomy | Surgery that severs connections between the cerebral hemispheres. | Explain how split-brain participants differed from typical participants. |
Contralateral | Relating to the opposite side of the body or visual field. | Work out which hemisphere receives or controls information. |
Visual field | The area visible to a person while looking at a particular point. | Identify which hemisphere receives a briefly presented stimulus. |
Left visual field | The left half of visual space, processed primarily by the right hemisphere. | Apply split-brain findings to a stimulus presented on the left. |
Right visual field | The right half of visual space, processed primarily by the left hemisphere. | Apply split-brain findings to a stimulus presented on the right. |
Fixation point | A central point that participants must continue looking at during visual presentation. | Explain how researchers control which hemisphere receives information. |
Tactile task | A task involving information received through touch. | Explain how objects placed in one hand are processed. |
Interhemispheric communication | The transfer of information between the two hemispheres. | Explain the normal function of the corpus callosum. |
Language lateralisation | The tendency for language functions to be mainly controlled by the left hemisphere. | Explain verbal findings from split-brain research. |
Visuospatial processing | Processing the position, shape and arrangement of visual information. | Explain a relative strength of the right hemisphere. |
Ecological validity | The extent to which findings represent behaviour in everyday situations. | Evaluate the artificial nature of split-brain tasks. |
Generalisation | Applying findings beyond the participants who were studied. | Evaluate the small and unusual sample. |
Brain plasticity | The brain’s ability to change through experience or following damage. | Explain why split-brain performance may change over time. |
Common Mistakes ⚠️
Mistake: Describing lateralisation and localisation as the same concept.
Why this is incorrect:Localisation concerns specialised areas, whereas lateralisation concerns differences between the two hemispheres.
How to improve:State clearly whether you are discussing a specific region or hemispheric dominance.
Mistake: Saying that the left eye sends information only to the right hemisphere.
Why this is incorrect:Visual information is divided according to visual fields, not individual eyes.
How to improve:Remember: left visual field to right hemisphere, right visual field to left hemisphere.
Mistake: Saying that the left hemisphere controls the left hand.
Why this is incorrect:Motor control is mainly contralateral.
How to improve:Remember: left hemisphere controls the right hand, and right hemisphere controls the left hand.
Mistake: Saying split-brain participants had one cerebral hemisphere removed.
Why this is incorrect:Both hemispheres remained. The corpus callosum connecting them was severed.
How to improve:Describe split-brain surgery as disrupting communication between the hemispheres.
Mistake: Assuming that a participant who cannot name an object has not processed it.
Why this is incorrect:The right hemisphere may process the object and guide the left hand even when the left hemisphere cannot name it.
How to improve:Distinguish verbal reporting from non-verbal recognition.
Mistake: Saying that information presented to the left visual field reaches the left hemisphere.
Why this is incorrect:Visual information is processed contralaterally.
How to improve:Use the rule: left visual field to right hemisphere.
Mistake: Saying that the right hemisphere has no language ability at all.
Why this is incorrect:Language is usually dominated by the left hemisphere, but the right hemisphere can contribute to communication and may process some simple verbal information.
How to improve:Describe language as mainly left-lateralised rather than completely absent from the right hemisphere.
Mistake: Describing the hemispheres as two entirely independent brains.
Why this is incorrect:In an intact brain, the hemispheres communicate and work together through the corpus callosum.
How to improve:Refer to specialised but integrated processing.
Mistake: Claiming that people are either left-brained or right-brained.
Why this is incorrect:Complex behaviour normally involves networks across both hemispheres.
How to improve:Use lateralisation to describe relative specialisation, not personality types.
Mistake: Ignoring the participants’ epilepsy when evaluating Sperry’s research.
Why this is incorrect:Epilepsy, medication and surgery may have influenced brain functioning and performance.
How to improve:Consider participant variables and limits to generalisation.
Mistake: Saying controlled procedures automatically produce high ecological validity.
Why this is incorrect:Control can improve reliability while making the task less representative of everyday behaviour.
How to improve:Balance scientific control against the artificiality of brief visual-field tasks.
Mistake: Giving findings without explaining the procedure.
Why this is incorrect:The findings make sense only when the examiner understands how information was directed to one hemisphere.
How to improve:Refer to fixation, brief presentation, visual fields and the severed corpus callosum.
Exam-Style Questions ✍️
Question 1
Which one of the following best defines hemispheric lateralisation?
A. The ability of the brain to recover after trauma
B. The principle that some functions are mainly associated with one hemisphere
C. The idea that every function occurs equally throughout the brain
D. The process of passing neurotransmitters across a synapse
[1 mark]
Question 2
Define the term corpus callosum.
[2 marks]
Question 3
Explain one difference between localisation of function and hemispheric lateralisation.
[4 marks]
Question 4
Describe how visual information was presented to participants in split-brain research.
[4 marks]
Question 5
A word is presented briefly in the right visual field of a split-brain participant.
Explain how the participant is likely to respond when asked to say what they saw.
[4 marks]
Question 6
A picture of a key is presented briefly in the left visual field of a split-brain participant.
The participant is then asked to:
Say what they saw.
Select the matching object using their left hand.
Explain the participant’s likely responses.
[6 marks]
Question 7
A split-brain participant closes their eyes while an object is placed in their left hand.
Explain why the participant may be able to use the object correctly but remain unable to name it.
[4 marks]
Question 8
Outline two findings from split-brain research.
[4 marks]
Question 9
Explain one strength and one limitation of Sperry’s split-brain research.
[6 marks]
Question 10
Discuss research into hemispheric lateralisation.
Refer to split-brain research in your answer.
[8 marks]
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