Sperry (classic Study) Flashcards
Lateralisation of function
The brain has left and right hemisphere and each hemisphere has a specific function
Left hemisphere specialises in…
Language and articulation of words
Right hemisphere specialises in
Emotions and creativity
What side of the body does the left hemisphere control?
Right side:
Right hand
Right field of view
What side of the body does the right hemisphere control?
The left side:
The left hand
The left field of view
What part of the brain links the 2 hemispheres?
The corpus callosum: bundle of the nerve fibres so signals can be spread across 2 hemispheres
Why would we cut the corpus callosum and separate the 2 hemispheres?
If someone had severe epilepsy: abnormal electrical impulses that cause seizures couldn’t spread across the brain if cut
Background of this study
Sherry had worked on split brain cats, and knew that 1 hemisphere could be completely oblivious to something the other hemisphere was taught: so test on humans
Using epilepsy patients who had corpus callosum cut
Aim of this study
Map lateralisation of brain function (aka determine function of 2 hemispheres) by presenting info to only 1 hemisphere in split brain patients and determining ability in tactile and visual tasks
The 3 experiments
Visual investigations
Tactile investigations
Right hemisphere tests
What type of study is this and why?
A quasi experiment because the independent variable, whether the participant was split brained or not, was naturally occurring
Independent variable
Whether participants were split brained or not
Dependent variable
The responses participants had to the tactile and visual tasks given
Experimental design
Independent measures: 2 categories of split brain compared to not split brain
We cannot manipulate this to be repeated measures
Sample size
11 split brain patients
9 recently undergone surgery
2 had it years before
Sample method
Opportunity
The apparatus name
Tachiotoscope
The set up 💯
Image back projected onto a screen the participant would look at
With a spot in the middle
Tactile objects behind screen out of view
Participants were told to…
Focus on the spot in the middle
When an image is presented to either side of the dot
Then the opposite hemisphere will internalise it and can perform actions based on its function
Field of view meaning
Either the eight side of the vision or left side
This is independent of left/right eyeballs: left field of view foes to right hemisphere and vice versa
Why project the image for 1/10 of a second?
To prevent eyes from moving to the image, we want to project the image to either enter the right or left field of view
We don’t want it to be the focus thus have it enter both hemispheres
How can we ensure that the information doesn’t enter both hemispheres?
Have participants sit in silence, information not sent to hemisphere by outwards speech
Have participant hide hands, only opposite hemisphere can control this hand so information not transferred by visually seeing the hands
In the visual investigations, when the image of key is shown to the right visual field what happens?
Information goes to left hemisphere which controls the language
So participant can say what they see, ‘key’
In the visual investigations, when the image of key is shown to the right visual field what happens?
Information goes to left hemisphere which controls the language
So participant can say what they see, ‘key’
In the visual investigations, when the image of key is shown to the left visual field what happens?
The information goes to the right hemisphere which controls emotions and creativity
The participant could use left hand to draw it but NOT name it
In the visual investigations, when the image of key is shown to the right visual field but an apple is shown to left visual field what happens?
Info of apple is sent to right hemisphere thus they can draw it with eyes closed using left hand
Info of key is sent to left hemisphere thus they say the image they saw was of a key and have no awareness of apple
Not understand why they drew an apple
In the tactile investigations, what happens when an object is given to the right hand
Information goes to left hemisphere so they could name what the object is
In the tactile investigations what happens when an object is put in the left hand?
Information goes to right hemisphere so they seem to have no conscious awareness of it (cannot name it)
But can point to it and find it by touch
Why are we Testing the right hemisphere specifically?
To see if the right hemisphere is able to make mental associations since we cannot use speech to show this (easy way)
Showing simple maths problems to the left field of view
Info Goes to right hemisphere
The left hand was able to solve this using blocks
But not solve this verbally
Presenting images to both visual field then showing a nude photo to the left visual field only
Participants could say they saw the shapes because shapes sent to both hemispheres
But showed non verbal cue eg giggle or blush when shown the nude, because nude info only went to right Visual field (controls emotions) but could not articulate why they giggled
Evaluate ecological validity
Tactile tasks have high ecological validity: reaching for objects out of view may be realistic
But highly controlled set up eg covering eyes and hands, sitting in silence and being told to not move eyes and focus on one spot not reflective of real life: perhaps not accurate reflection of real life
Evaluate population validity
Used a mix of genders
But only from USA: individual differences occurring within this study means we do not know of brain lateralisation and effect of commisuorotomy are species specific
Evaluate construct validity
Highly controlled quasi experiment to show what we measured is due to split brain:
Hands hidden from view, sitting in silence, focus on spot, only shown for 1/10 sec, covered eyes
So no info can be transmitted to other hemisphere via the outside: we know we are measuring the function of each hemisphere
