Sperry

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  • Created by: Emily
  • Created on: 09-05-13 17:45

Relation to the physiological approach.

  • All that is pyschological is first physiological.
  • This approach could explain the difficulties experienced by individuals with a "split-brain" as their brains work differently to those of "normal" people.
  • As a result of having their corpus callosum severed, the two hemispheres of the brain work independently and, unlike a "normal" brain, do not transfer info from one side to the other.
  • This inability to transfer info means that split-brain patients cannot do certain things a "normal" person can.
  • This was shown in Sperry's study, this showed that if an object was presented in the left visual field, which was registered by the right hempishere of split-brain patients, they were unable to name what they had seen.
  • A "normal" person would have no difficulty naming the object.
  • This is because the language centre of the brain is in the left hemisphere, and in split-brain patients, info presented to the right hemisphere cannot be transferred to the left for indentification through language.
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Background.

  • Previous research using split-brain animals showed numerous behavioural effects (Myers 1961: Sperry, 1967.)
  • Other research by Sperry, on humans and monkeys that had undergone surgical section of the corpus callosum, suggested the behavioural effects of this surgery may be less severe than other forms of ceberbral surgery.
  • Research by Akelaitis (1944) also showed no important behavioural effects of surgical section of the corpus callosum in humans, provided other brain damage was excluded.
  • More recent research by Sperry using appropriate tests, has actually shown a large number of behavioural effects that correlate directly with the loss of the neocratical commissure in man as well as animals.
  • Sperry therefore set out in this study using split-brain patients, to show how each hemisphere:

     -Possesses an independent stream of conscious awareness.

     -Has its own seperate chain of memories that are inaccessible to the other hemisphere.

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Theories on which the study is based.

  • 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 Wernike's area, respectively) showing their functional localisation
  • The primary motor cortex is situated in the frontal lobe, and areas in the right hemisphere recieve info from and are concerned with the activities of the left side of the body and vice versa.
  • Sperry believes that the studies involving split-brain patients reveal the "true" nature of the 2 hemispheres, because a commissurotomy, which deconnects the 2 hemispheres, means they can only work independently.
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Research Method.

  • Natural/Quasi experiment as the IV (having a split-brain or not) was not directly manipulated by the researchers.
  • Participants with split-brains had already undergone hemisphere deconnection to reduce severe epilepsy.
  • No control group needed as the functions and abilities of the visual fields and hemispheres in non-split-brains were already known.
  • The DV was the participants ability to perform a variety of visual and tactile tests.
  • Can be considered a collection of case studies as the extensive tasks were carried out on a small sample size (11 participants.)
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Presenting Visual Information.

  • The participant, with one eye covered, centred the gaze on a fixed point in the centre of an upright translucent screen.
  • Visual stimuli on 35mm transparecies were arranged in a standard projector and were then back-projected at one-tenth of a second or less- too fast for eye movements to get the info into the wrong visual field.
  • 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 which eye is used.)
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Presenting Tactile Information.

  • Below the screen there was a gap so that participants could reach objects but not see their hands.
  • Objects were then placed in either the person's right/left or both hands.
  • Information about the objects placed in the left hand is processed by the right hemisphere and vice versa.
  • Participants undertook a variety of both visual and tactile tests.
  • This apparatus is called a tachistoscope.
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Key Findings Visual Tests.

  • Info shown and responded to in one visual field could only be recognised again if shown to the same visual field.
  • Info presented to the RVF could be described in speech and writing (with the right hand)
  • If the same info is presented to the LVF participants insisted either that they did not see anything or that there was only a flash of light on the left side - that is, the info couldn't be described in speech or writing.
  • However, participants could point with the left hand to a matching picture/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), participants could draw the $ sign witht the left hand but reported that they had seen a ?.
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Conclusions.

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

Usefulness:

  • Helping patients with brain damage.
  • Before, little was known about the abilities of the right (minor) hemisphere, but now tests show that this hemisphere has a range of higher-order mental abilities, including some verbal comprehension. and it is dominant in such abilities as spatial awareness and emotion.
  • The study revealed the importance of the corpus collosum as a pathway for internal communication between 2 sides of brain and behavioural limitations that may result from damage to it.
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