AS level Psychology The Core studies

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AS level PsychologyThe Core studies
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The Split Brain Studies - R Sperry 1968

• THREE Questions...
• What happens when the two halves of the brain are
  disconnected?
• Do the hemispheres perform different functions?
• Does each hemisphere have its own memories,
  perceptions and concepts?

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Some background.

• Why are there two halves to the brain?
• The corpus callosum joins the two halves of the
  brain
• A commissurotomy is the division of the two
  hemispheres by surgery

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The two hemispheres

• The RIGHT side of the brain processes info from
  LEFT half of body
• The LEFT side of brain processes info from RIGHT
  half of body
• VISUAL PATHWAYS CROSS OVER

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Brain Functions

• The supposition
• The left half of the brain is specialised for
  language
• linguistic expression both symbolic and logical
• The right half of the brain is specialised for
  perception
• visuospatial and artistic

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Brain Functions

• Can this be supported by evidence?
• Sperrys experiment was
• A NATURAL EXPERIMENT
• 11 participants
• Sperrys Ps were epileptics who could not be
  treated with drugs

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The split brain procedure

• The subject has one eye covered
• Gazes at a fixation point on an upright
  translucent screen
• slides are projected either side of the fixation
  point for 1/10th sec

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The split brain procedure

• What happened?
• When an object is displayed on one half of the
  screen (ie the left) and then in the other the P
  has no recollection of seeing it before
• TWO SEPARATE MEMORIES?

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The split brain procedure

• Speech and writing
• When an object is displayed in the right visual
  field (thus processed in the left hemisphere) Ps
  can describe it in speech and writing

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The split brain procedure

• Speech and writing
• When an object is displayed in the left visual
  field (thus processed in the right hemisphere) Ps
  insist they have not seen anything
• BUT
• if asked to use the LEFT HAND to point to a
  matching object on the table can do so, while
  STILL insisting nothing was seen

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The split brain procedure

• TWO different objects displayed
• e.g. CASE and KEY
• Ps asked to draw what they see with their left
  hand
• DREW what was on the LEFT half of the screen
  (CASE)
• BUT said they had drawn what was on the RIGHT
  half of the screen (KEY)

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The split brain procedure

• OBJECTS placed in RIGHT HAND for IDENTIFICATION
  BY TOUCH
• Ps described the object in speech and writing
• OBJECTS placed in LEFT HAND for IDENTIFICATION
  BY TOUCH
• Ps made wild guesses - seemed unaware of object
  in their hand

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The split brain procedure

• Two different objects placed in each hand - then
  hidden for retrieval in pile of items
• Each hand hunts searching for its own object but
  ...If the left hand picks up the object which the
  right hand is looking for, the object is
  rejected but the other hand continues to
  search!!!

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The split brain procedure

• An APPLE flashed LEFT side of the screen
• If the P uses his LEFT HAND to find an apple on
  the table he cannot name each object he picks
  up but can pick up the apple
• If he uses his RIGHT HAND he can name each object
  he picks up - but cannot SAY what his RIGHT hand
  is searching for
• Because the RIGHT hemisphere that could recognise
  the correct answer gets no feedback from the
  RIGHT hand

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Has the right hemisphere the ability to process
language?
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• The hemisphere that processes language (usually
  the left) is known as the major hemisphere.
• The other hemisphere is known as the minor
  hemisphere.
• Sperry was able to demonstrate limited language
  processing ability in the minor (right)
  hemisphere.
• In one experiment a picture of a wall clock would
  be shown to the minor hemisphere, and the patient
  was able to pick out a wristwatch with the left
  hand (which is controlled by the right
  hemisphere).

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• As a wristwatch is physically nothing like a wall
  clock, it can be assumed that the patient was not
  guided by a visual image alone.
• It is reasonable to assume that semantic
  processing took place, as the link between the
  two objects (being their similarity of function)
  is purely semantic.
• In another experiment, when the subject was asked
  to pick out a 'piece of silverware', for example,
  their left hand could successfully retrieve a
  fork.

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Can the right hemisphere perform calculations?

• Sperry was also able to demonstrate that the
  right hemisphere can perform simple arithmetical
  calculations. This is normally more efficiently
  performed within the left hemisphere. Simple sums
  would be presented to the left visual field, and
  therefore processed by the right hemisphere. The
  left hand was able to indicate the answer by
  pointing to or writing the correct answer.

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Emotion in the right hemisphere

• The minor (right) hemisphere can express emotion.
  A pin-up of a nude presented in the left visual
  field (and hence processed by the right
  hemisphere) would produce blushing or giggling,
  but no verbal report of having seen the picture.

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Emotion in the right hemisphere

• An unpleasant smell presented to the right
  hemisphere (through the right nostril) would
  produce the response 'phew' but no verbal report
  of what the smell was like.

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The split brain procedure

• Conclusion
• It seems that one half of the brain does not know
  what the other half is doing

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The split brain procedure

• SUMMARY
• The LEFT hemisphere (in right handed people) is
  specialised for speech and writing and for the
  organisation of language
• It can communicate the visual experiences of the
  RIGHT VISUAL FIELD and about the experiences of
  the RIGHT half of the body

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The split brain procedure

• SUMMARY
• The RIGHT hemisphere is MUTE and cannot speak or
  write
• (aphasic and agraphic)
• but can show NON VERBALLY that mental processes,
  centred around the LEFT VISUAL FIELD and the LEFT
  half of the BODY, are present

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Role of each HemisphereLeft Right

• Speech
• Production of speech, comprehension of the
  literal meaning of speech

• Emotional inflections, understanding jokes
  humour, sarcasm, emotional content of speech

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Role of each HemisphereLeft Right

• Auditory System 
• Sounds related to speech
• Emotions
• Expressions of happiness

• Non-language environmental sounds (e.g.,
  rain)Music
• Expressions of anger, fear, disgust interpreting
  the emotional expressions of other people

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Role of each HemisphereLeft Right

• Vision
• Details

• Overall configuration spatial processing (e.g.,
  arranging pieces of a puzzle or drawing a picture)

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Role of each HemisphereLeft Right

• Mode or Style
• (How data are processed)
• Details, parts, pieces 

• Gestalt,
• overall configuration
• global form 

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Role of each HemisphereLeft Right

• Spatial Frequency Hypothesis
• (What data are processed) 
• High spatial frequency
• many and frequent visual changes 

• Low spatial frequencies
• few visual changes 

In the following examples what layout do you
prefer?
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Role of each HemisphereLeft Right
Low spatial frequencies
High spatial frequency
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Role of each HemisphereRight Left
High spatial frequency
Low spatial frequencies
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EVALUATION Criticism

• The Ps were epileptic -
• CAN they be said to represent NORMAL brains?
• INDIVIDUAL DIFFERENCES - some people have more
  lateralised brains

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EVALUATION Criticism

• SEX DIFFERENCES
• Women have less lateralised brains
• Perhaps RIGHT HANDED male brains are more RIGHT
  ltgt LEFT specialised?
• KIMURA reported more aphasia in men who had left
  brain damage

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EVALUATION Criticism

• A REDUCTIONIST explanation for human behaviour
• (BRAIN not MIND)
• Most tasks involve a mixture of LEFT and RIGHT
  brain skills
• When we hear speech we decode meaning from the
  WORDS AND the EMOTIONAL TONE in the voice

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The split brain procedure

• Do the two halves of the brain represent two
  minds?
• Evidence
• Hemispherectomy - the removal of one half of the
  brain..
• the SELF remained

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The split brain procedure

• SPERRY said
• When the brain is disconnected we see two
  separate selves, each with its own memory and
  will

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The split brain procedure

• MACKAY (1987) said...
• Not TWO people with TWO free wills... but one
  person who under certain circumstances is liable
  to show a strange form of absent mindedness

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The split brain procedure

• What do you think?

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SPERRY - QUESTIONS

• Does the size of the sample matter?
• What was unusual about the participants?
• Why was this a NATURAL experiment?
• What was the IV?
• Are there any ethical problems?

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Roger Sperry (1968) was given a NOBEL PRIZE for
this research

• READ this study up
• THE END