Sperry

What was the background to this study?

Focused on epilepsy. In the 1940s a treatment was developed called ‘split brain surgery’ (commissurotomy) that included the corpus callosum being cut so that the abnormal electrical impulses could not spread throughout the brain. Sperry thought patients who’d undergone this surgery were perfect to study what each hemisphere of the brain does.

Define lateralisation of function

One side of the brain has a different role from the other.

Define corpus callosum

Fibres that carry the majority if information between the two hemispheres of the brain.

Define contralateral control

The idea that each side of your body is controlled by the other side of your brain.

Define commissurotomy

Surgical operations to sever the corpus callosum.

What was the overall aim?

To study the functions of separated and independent hemispheres.

Describe the sample used in the study

Epileptic- 11 patients (male and female) who had undergone a commissurotomy as a treatment for their epilepsy. They were obtained from a surgery within America.

Non epileptic- group of people who had not undergone surgery.

What are some strengths and weaknesses of the sample?

Strengths

• Able to test the hemispheres independently as they were separated in the surgery

Weaknesses

• Small sample size

• 2 people had the surgery 4-5 years ago so may have recovered

• Perhaps the cause of results was epilepsy

How was the tachistoscope used?

It’s a piece of equipment that allows researchers to show participants images to only one of the visual fields in each eye. The images are presented for 0.1 seconds.

What controls were used?

• The items

• The images/lasted same time

• The fixation point

• Hands out of view

• Symbols displayed

• One eye covered

• Set up of tachistoscope

Describe 2 things Sperry found during the visual tasks

1. Objects were flashed to the right visual field-went to the left hemisphere-participant COULD name the object verbally

2. Objects were flashed to the left visual field-went to the right hemisphere-participant COULD draw or point to object with left hand-participant COULD NOT say what they’d seen

Describe what Sperry found during the tactile tasks

1. Objects were felt by the right hand (unseen)-went to left hemisphere-participant COULD name what they’d felt or write it

2. Objects were felt by the left hand (unseen)-went to right hemisphere-participant COULD find/point to object with left hand-participant COULD NOT say what they’d held

What did Sperry conclude about the left hemisphere?

It has language ability (both written and verbal) and controls the right hand side of your body.

What did Sperry conclude about the right hemisphere?

It can only communicate non-verbally and controls the left hand side of your body.

What ethical guidelines were upheld and broken?

Upheld

• Confidentiality

• Informed consent

• Deception

Broke

• Protection from harm- upsetting/embarrassing to not have full capabilities or understanding present

• Debrief- not clear if they had one

Evaluate the ethnocentrism

Quite ethnocentric because it’s only participants from America but since it’s linked to the brain it’s global + applicable.

Evaluate the reliability

Internal reliability

Very standardised as many things were controlled and each participant likely had the same experience e.g. images shown for 0.1 seconds

External reliability

• Only 11 people who had epilepsy so small sample, no consistent effect

Evaluate the validity

Construct validity

• Epilepsy could’ve effected the results

Population validity

• All Americans

• Both genders

• Specific to epileptic people who have had split brain surgery

Ecological validity

• Visual tasks- not normal to be flashed images through a tachistoscope + for only 0.1 seconds

• Tactile tasks- normal to touch objects daily without seeing hands e.g. in the dark

Which debates does this study link to and why?

• Nature vs nurture- your brain is biological and there’s no influence from environment

• Reductionism vs holism- only looking at hemisphere of brain/biological reasons

• Usefulness of research- useful since it shows how each hemisphere of the brain works and can be used in medicine for potential brain injuries and peoples’ capabilities + support needed