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Background:
Theory:
Sperry himself had conducted similar previous research on cats and monkeys with split brains. The LH of the brain is responsible for speech and the RH is responsible for more creative acts. The RH is known as the 'speechless right' as it would not be able to say what it can see without assistance from the LH. Sperry wanted to test if his thoughts were true to human split brain patients. You should also know that Sperry was awarded the NOBEL PRIZE as a result of his work and findings on the animals.
Aim:
Experimental Design: Repeated measures (ps were used for all the tasks)
IV: Whether someone has their corpus callosum severed
DV: Ps performance on various tactile and visual tasks
Sampling Technique: Opportunity (Sperry took advantage of the ps that were available to be studied)
Sample:
VISUAL:
Evaluation:
Method:
+ = Enables researcher to investigate variables that are not able to be investigated in strict lab experiments
+ = Sperry developed techniques to allow the 2 hemispheres of the brain to be studied, which was previously IMPOSSIBLE
+ = Highly controlled, objective lab equipment and procedures. E.g all ps had to be silent during the visual and tactile tasks.
+ = Quasi- allows investigation of lateralisation of function of hemispheres. E.g ps already had split brains --> corpus callosum and speechless right can be studied
+ = The apparatus designed by Sperry was a scientific breakthrough, allowing these patients to be studied for the 1st time.
-= Quasi, limited control over IV
Sample:
+ = Sperry made good use out of the few ps available for the study who had undergone surgery to sever their corpus callosum (approx only 60 people have had the surgery), so in this way the sample can be considered relatively large.
+ = As all 11 ps experienced SIMILAR effects, the sample is REPRESENTATIVE of people who are or have undergone the same operation as the ps in this study (a commisurotomy).
-= As Sperry didn't test the ps before they had the operation we do not know whether their brain functioning would have been atypical (different from the norm) before the operation. This would make it more difficult to draw CONCLUSIONS about the function of the hemispheres in non-separated brains.
- = Sample too small- not representative of the population of people who have severed corpus callosum's. For e.g they may answer the visual and tactile tasks differently to the other split brain patients.
- = Didn't test the ps before they had the surgery, this would have been good results to compare against.
Type of data:
+ = Mainly quant data, enabled conclusions to be drawn about the 2 different functioning hemispheres
+ = Qual data of the ps experiences during the study are important in helping us UNDERSTAND their experiences. E.g when ps denied they had saw a nude image presented to their RH, but laughed shows more about the functioning of the 'speechless right' than quantitative data could. So here the ps knew what they had saw was funny, but they didn't know what it was that they found funny.
+= As both qual and quant data used, VALIDITY and RELIABILITY are increased.
- = Qual-unable to compare
- = Quant-doesn't get rich meaningful data in why something could not be identified by the ps
Reliability:
+ = Sperry's work has been supported by other researchers
+ = Sperry's conclusion that the 2 spheres of consciousness with their own private sensations, perceptions, thoughts, feelings and memories is now ACCEPTED.
- = Individual differences have not been taken into account-making the study REDUCTIONIST, for ot considering other reasons that the ps brains may have functioned in the way they did.
- = It can be argued that if the ps were tested a long time after their operation there may have been different results found, as their brains might have undergone significant reorganisation, onset by long-standing abnormalities. E.g their brains may have adjusted to their new arrangement and their anterior commissure . may adapt and be able to transfer larger bits of info from one hemisphere to the other over a long period of time.
- = More RECENT research has suggested that the degree of separation of the 2 hemispheres in NORMAL people is perhaps not as great as once thought. This means each hemisphere does some of the function that the other hemisphere is known for doing. E.g it has been demonstrated that the RH has some understanding of language (which we normally associate with being with the LH) and that the LH may have the responsibility for the production of imagery (which we normally associate with being with the RH)
Validity:
+ = Revealed facts about the lateralisation of functions between the 2 hemispheres that had previously only been suggested in previous studies
+= Having their corpus callosum severed was a part of the ps life, so high in ecol valid
- = Low Ecol valid as Sperry's techniques artificially separate the visual and tactile information received by the individual. Recognition of an object/patients ability to use hemispheres independently doesn't affect them in real life as they can use both their hands and visual fields together to identify what is presented to them. It was conducted in ARTIFICIAL SETTING as images not normally seen for 1/10 of a second, through just one visual field. In real life they would have time to compensate by moving their eyes so the material is received by both visual fields allowing them to correctly identify the material.
Ethics:
+ = Used ps who had had their corpus callosum severed to control their epilepsy and NOT for the purpose of the research.
Improvements & Implications:
1) Sample:
Increase sample size from 11 to 30. Would go through the relevant hospitals clinical database to find the patients that have had the operation and them invite them take part in the study.
Get ps to do visual and tactile tasks BEFORE and after they have their operation. Would go through the relevant hospitals clinical database to find the patients that have had the operation and them invite them take part in the study.
- Sperry was interested in the connection between brain structure and behaviour.
- Corpus callosum- largest bundle of nerves that connects the LH and RH. It allows info to be COMMUNICATED from one hemisphere of the brain to the other. This means info from the LH can be interpreted by the RH an vise versa.
- Anterior commissure- can communicate BASIC info and EMOTIONAL responses to either hemisphere as it is not severed, but is LIMITED as it cannot communicate complex responses, which would have helped the brain be more aware of its surroundings.
- People who suffer from severe epilepsy and cannot be treated effectively with drugs can have an operation called a COMMISUROTOMY to DISCONNECT the 2 hemispheres to LIMIT the damage from an epileptic seizure (caused by the storm of ELECTRICAL ACTIVITY in the brain).
- Once patient had the operation it was almost as if they had 2 SEPARATE brains that both work INDEPENDENTLY. Theses were the types of ps Sperry used in his study.
- Note: 'Split brain' refers to patients that had undergone the operation to sever the corpus callosum. 'Visual field' refers to the eye of the ps, i.e Left or Right, hence LVF and RVF. The LH is responsible for the RHS of the body and vise versa.
- HEMISPHERE DECONNECTION- The two cerebral hemispheres have been disconnected through severing the connecting tissue known as the corpus callosum.
- FOR A MORE INTERACTIVE INSIGHT INTO EPILEPSY (WHICH MAY BE INTERESTING TO THOSE OF YOU WHO WANT TO KNOW MORE OF THE BACKGROUND INTO EPILEPSY), CHECK OUT THIS FROM HEALTHLINE:
Theory:
Sperry himself had conducted similar previous research on cats and monkeys with split brains. The LH of the brain is responsible for speech and the RH is responsible for more creative acts. The RH is known as the 'speechless right' as it would not be able to say what it can see without assistance from the LH. Sperry wanted to test if his thoughts were true to human split brain patients. You should also know that Sperry was awarded the NOBEL PRIZE as a result of his work and findings on the animals.
Aim:
- To investigate the functions of separated hemispheres of the brain a severed corpus callosum on the functioning of the 2 brain hemispheres
- To show that the LH and RH have different functions.
- To show that info from one hemisphere is not accessible from the other hemisphere without the corpus callosum.
- (Basically: to test the functioning of separated and independent hemispheres).
Experimental Design: Repeated measures (ps were used for all the tasks)
IV: Whether someone has their corpus callosum severed
DV: Ps performance on various tactile and visual tasks
Sampling Technique: Opportunity (Sperry took advantage of the ps that were available to be studied)
Sample:
- 11 patients
- whom had had an operation to sever their corpus callosum in an attempt to reduce the severity of their epileptic seizures
- 2 had been operated on a long period before the experiments took place. The other 9 had RECENTLY undergone surgery.
- (Note: during the several years it took to complete the study, each ps was tested at one point of time during this period).
- ps had to be SILENT during the study, unless asked a Q by the experimenter.
- the experimenter controlled which visual field receives the info as the stimuli is flashed for 1/10 of a second.
- The ps had one eye covered and was asked to gaze at a fixation point in the centre of a projector screen in front of them. Visual stimuli were back-projected onto the screen, either to the right or left of the screen, at a very high speed– one picture every 1/10th of a second or less. This meant that the eye only had time to process the image in the visual field where it was placed (ie if the image was shown to the left visual field there was not time for the ps to move their eye or head so the right visual field might also receive the image). Below the screen was a gap so the ps could reach objects but not see his or her hands. Visual investigations were then conducted which involved flashing one stimuli at a time to one visual field or two stimuli simultaneously to different fields and ps were asked to identify what they saw through speech, writing or drawing.
- Tactile investigations involved placing an object in one hand or the other, or both hand simultaneously without the ps being able to see what they were holding and then asking them to identify what they had been holding through speech, writing, drawing or manual selection from various objects.
- ps had to cover one eye
- ps had to be silent during the study unless asked a Q by the experimenter
VISUAL:
- Information presented to the RVF could be described in SPEECH and writing (as it would be processed by the LH, which is responsible for speech).
- Information presented to the LVF could not be identified through speech or writing, (hence the RH is named 'speechless right'. In fact they will INSIST they haven't seen anything).
- Information presented to the LVF could be identified non-verbally (e.g pointing with the left hand).
- If DIFFERENT images are SIMULTANEOUSLY FLASHED to each visual fields and the ps was asked to DRAW what they had saw using their out of sight LEFT HAND, they will regularly draw the image that they saw in the LVF. However if they are asked what he had drawn he would say the image that had been presented to the RVF.
- If two different words were flashed simultaneously to the right and left visual fields the participant would select with the left hand the object presented to the left visual field but if asked to write the word with the right hand or spell out the word he would write or spell the word presented to the right visual field
- If information was presented to one visual field it could only be recognised again if presented to the same visual field (as the other hemisphere is unaware of having seen it before. If the same image was presented to the other visual field, the ps would respond as if seeing the visual stimuli for the 1st time).
- An object placed in the ps right hand could be identified or named in speech or writing whereas if the same object was placed in the left hand the ps could only make wild guesses/seemed unaware that they had been given anything.
- Confirm that patients who have had their corpus callosum severed effectively have '2 minds in the same body'.
- Hemispheres operate independently in slit brain patients, but emotions can be transferred across (through the anterior commissure- fires that also connects the 2 hemispheres).
- The right hemisphere controls emotional responses.
- Language skills are based in the left hemisphere.
- The left hemisphere controls words and the ability to speak.
- The left hemisphere allows us to reason things out.
- The right hemisphere is the ‘pictures’ hemisphere and specialises in tasks such as drawing, spatial awareness and intuitive tasks.
- Information received by one hemisphere is not accessible to the other hemisphere in split-brain patients (There is no transfer in info between the hemispheres).
- The individual has separate streams of consciousness.
- Objects placed in right hand are identified by left hemisphere which controls speech.
- Objects placed in left hand are identified by right hemisphere which has no speech capacity.
- Objects can only be retrieved by the same hand because information cannot be passed to the opposite hemisphere as the corpus callosum had been severed.
- Two objects can be retrieved at the same time with the original hand because the hemispheres work independently.
- Because split-brain people have had the two hemispheres deconnected so information cannot be passed across/the two hemispheres cannot communicate with each other.
Evaluation:
Method:
+ = Enables researcher to investigate variables that are not able to be investigated in strict lab experiments
+ = Sperry developed techniques to allow the 2 hemispheres of the brain to be studied, which was previously IMPOSSIBLE
+ = Highly controlled, objective lab equipment and procedures. E.g all ps had to be silent during the visual and tactile tasks.
+ = Quasi- allows investigation of lateralisation of function of hemispheres. E.g ps already had split brains --> corpus callosum and speechless right can be studied
+ = The apparatus designed by Sperry was a scientific breakthrough, allowing these patients to be studied for the 1st time.
-= Quasi, limited control over IV
Sample:
+ = Sperry made good use out of the few ps available for the study who had undergone surgery to sever their corpus callosum (approx only 60 people have had the surgery), so in this way the sample can be considered relatively large.
+ = As all 11 ps experienced SIMILAR effects, the sample is REPRESENTATIVE of people who are or have undergone the same operation as the ps in this study (a commisurotomy).
-= As Sperry didn't test the ps before they had the operation we do not know whether their brain functioning would have been atypical (different from the norm) before the operation. This would make it more difficult to draw CONCLUSIONS about the function of the hemispheres in non-separated brains.
- = Sample too small- not representative of the population of people who have severed corpus callosum's. For e.g they may answer the visual and tactile tasks differently to the other split brain patients.
- = Didn't test the ps before they had the surgery, this would have been good results to compare against.
Type of data:
+ = Mainly quant data, enabled conclusions to be drawn about the 2 different functioning hemispheres
+ = Qual data of the ps experiences during the study are important in helping us UNDERSTAND their experiences. E.g when ps denied they had saw a nude image presented to their RH, but laughed shows more about the functioning of the 'speechless right' than quantitative data could. So here the ps knew what they had saw was funny, but they didn't know what it was that they found funny.
+= As both qual and quant data used, VALIDITY and RELIABILITY are increased.
- = Qual-unable to compare
- = Quant-doesn't get rich meaningful data in why something could not be identified by the ps
Reliability:
+ = Sperry's work has been supported by other researchers
+ = Sperry's conclusion that the 2 spheres of consciousness with their own private sensations, perceptions, thoughts, feelings and memories is now ACCEPTED.
- = Individual differences have not been taken into account-making the study REDUCTIONIST, for ot considering other reasons that the ps brains may have functioned in the way they did.
- = It can be argued that if the ps were tested a long time after their operation there may have been different results found, as their brains might have undergone significant reorganisation, onset by long-standing abnormalities. E.g their brains may have adjusted to their new arrangement and their anterior commissure . may adapt and be able to transfer larger bits of info from one hemisphere to the other over a long period of time.
- = More RECENT research has suggested that the degree of separation of the 2 hemispheres in NORMAL people is perhaps not as great as once thought. This means each hemisphere does some of the function that the other hemisphere is known for doing. E.g it has been demonstrated that the RH has some understanding of language (which we normally associate with being with the LH) and that the LH may have the responsibility for the production of imagery (which we normally associate with being with the RH)
Validity:
+ = Revealed facts about the lateralisation of functions between the 2 hemispheres that had previously only been suggested in previous studies
+= Having their corpus callosum severed was a part of the ps life, so high in ecol valid
- = Low Ecol valid as Sperry's techniques artificially separate the visual and tactile information received by the individual. Recognition of an object/patients ability to use hemispheres independently doesn't affect them in real life as they can use both their hands and visual fields together to identify what is presented to them. It was conducted in ARTIFICIAL SETTING as images not normally seen for 1/10 of a second, through just one visual field. In real life they would have time to compensate by moving their eyes so the material is received by both visual fields allowing them to correctly identify the material.
Ethics:
+ = Used ps who had had their corpus callosum severed to control their epilepsy and NOT for the purpose of the research.
Improvements & Implications:
1) Sample:
Increase sample size from 11 to 30. Would go through the relevant hospitals clinical database to find the patients that have had the operation and them invite them take part in the study.
- += Sample more REPRESENTATIVE of the split brain patients
- - = Might not have 30 ps willing to take part and condition is rare so difficult to access and increase sample size
- - = Time CONSUMING
Get ps to do visual and tactile tasks BEFORE and after they have their operation. Would go through the relevant hospitals clinical database to find the patients that have had the operation and them invite them take part in the study.
- + = Individual differences would be considered and kept constant.
- + = Establishes C & E as we will know if the ps had abnormal functioning of the brain before they they took part in the split brain experiment.
- + = Would allow us compare functioning of the brain with and without their corpus callosum being severed.
- - = DCs are possible if ps realise the aim and falsify their results, (by e.g saying they hadn't seen the word when they had).
- - = Only get ps who have severe epilepsy- not representative as the majority of people don't have epilepsy.