Sperry

Question 1

Describe the background to Sperry’s study

Answer 1

• Earlier research using split-brain animals showed many behavioural effect.

Other research by Sperry on both humans and monkeys who had undergone surgical section of the corpus callous suggested the behavioural effect of this surgery may be less severe than other forms of cerebral e.g frontal lobotomy.

Research by akelaitis also showed no important behavioural effects of surgical section of the corpus callosum in humans, supplied other brain damage was excluded.

More recent research by Sperry et al using appropriate tests has shown many behavioural effects that correlate directly with the loss of the neocortical commissures in man as well as animals.

Question 2

What did Sperry set out to do in his study?

Answer 2

Wanted to show that each hemisphere:

1) possesses an independent stream of conscious awareness
2) Has its own separate chain of memories that are inaccessible to the other

Question 3

What theories lie on Sperry’s study?

Answer 3

• Although the right and left hemisphere are in many ways mirror images of each other, there are distinct areas dealing with speech production and comprehension (Broca’s area and Wermicke’s area, respectively) showing their functional localisation.
• Fuctional lateralisation also exists because Broca’s and Wernicke’s areas are only found in the left hemisphere.
• The primary motor cortex is situated in the frontal lobe and areas in the right hemisphere receive information from and are concerned with the activities of the left side of the body and vice versa.
• Sperry believes that studies involving split-brain patients reveal the ‘true’ nature of the two hemispheres because a commissurotomie which reconnects the two hemispheres mean they can only work independently.

Question 4

What was the experimental method?

Answer 4

Quasi experiment - All of the participants had a split brain

Question 5

What was the IV?

Answer 5

IV was having a split brain or not

Question 6

Why had the participants undergone split brain surgery?

Answer 6

Patients with split-brains had already undergone hemisphere reconnection to reduce severe epilepsy.

Question 7

Why was a control group not necessary?

Answer 7

A control group wasn’t necessary for comparison in this study because the functions and abilities of the visual fields and hemispheres in non-split-brain individuals was already known.

Question 8

What was the DV in this study?

Answer 8

The DV was the participant’s ability to perform a variety of visual and tactile tests.

Question 9

Why could Sperry’s study be considered to be a collection of case studies?

Answer 9

It has been argued that because such extensive tests were carried out on a very small sample

11 split brain patients in total

This study can be considered a collection of case studies

Question 10

Describe the sample in Sperry’s study

Answer 10

• 11 patients who had undergone ‘an extensive midline section of the cerebral commissures to control severe epileptic convulsions not controlled by medication’
• The 1st patience (Male) had his surgery over 5 1/2 years before the study was conducted
• The 2nd patient, mother in her 30s, had her surgery more than 4 years before the study.
• The other 9 patients had their surgery at varying times but not long before the study was conducted.

Question 11

What was the aim of Sperry’s study?

Answer 11

The aim of Sperry (1968) was to show the independent streams of conscious awareness possessed by each hemisphere and to show how each hemisphere has its own memories.

Question 12

What are the main functions of the left and right hemisphere of the brain?

Answer 12

The lefts role is language, reasoning and logical thought.

The right hemispheres function is creativity, imagination and spacial awareness.

Question 13

What hemispheres of the brain control each hand?

Answer 13

The right hemisphere controls of the left hand, while the left hemisphere controls the right hand.

Question 14

What were the key tests conducted?

Answer 14

• Visual test

* Tactile test

Question 15

Outline the procedure (VISUAL)

Answer 15

1) The participant, with one eye covered with an eye patch, centred his gaze on a fixed point in the centre of an upright translucent screen.
2) Visual stimuli on 35-millimetre transparencies were arranged in a standard projector and were then back-projected at 1/10 of a second or less
- too fast for eye movements to get the information into the wrong visual field.
3) Everything projected to the left of the central meridian of the screen is passed via the LVF to the right hemisphere and vice versa
- regardless of what eye is used.

Question 16

Outline the procedure (TACTILE)

Answer 16

1) Below the translucent screen there was a gap so that participants could reach objects but not see their hands.
2) Objects were then placed in either the participant’s right / left hand or both hands
3) Information about objects placed in the left hand is processed by the right hemisphere and vice versa.

Question 17

What apparatus did Sperry use?

Answer 17

• Tachistoscope

The tachistoscope has a focal point in the middle and two areas where stimuli was presented. The participants using the tachistoscope would have one eye covered and were instructed to stare at the focal point.

Question 18

What other tests did Sperry conduct?

Answer 18

• Sperry also conducted a variety of other tests which highlighted the lateralisation of brain function. These can be found in the original study.

Question 19

What were the key findings from Sperry’s study (VISUAL)

Answer 19

• Information shown and responded to in one visual field could only be recognised again if shown to the same visual field.
• Information presented to the RVF (LH of a right-handed person) could be described in speech and writing (Right-hand). If the same information is presented to the LVF (RH), the participant insisted he either did not see anything or that there was only a flash of light on the left side
• information couldn’t be described in speech or writing
• However, the participant could point with his left hand (RH) to a matching picture of object presented among a collection of pictures/objects.
• If different figures were presented simultaneously to different visual fields e.g., $ sign to the LVF and ? to the RVF, the participant could draw the $ sign with his left hand but reported that he had seen a ?

Question 20

What were the key findings in Sperry’s study? (TACTILE)

Answer 20

• Objects placed in the right hand (LH) could be described in speech or writing (with the right hand). If the same objects were placed in the left hand (RH) participants could only make wild guesses and often seemed unaware they were holding anything.
• Objects felt by one hand were only recognised again by the same hand e.g, objects first sensed by the right hand could not be retrieved by the left
• When two objects were placed simultaneously in each hand and then hidden in a pile of objects, both hands selected their own object and ignored the other hand’s object.

Question 21

What were the three possible conclusions from Sperry’s study?

Answer 21

1) People with split brains have two separate visual inner worlds, each with its own train of visual images.
2) Split-Brain patients have a lack of cross-integration where the second hemisphere does not know what the first hemisphere has been doing.
2) Split-brain patients seem to have two independent streams of consciousness, each with its own memories, perceptions and impulses i.e two minds in one body.