AS level Psychology The Core studies

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?

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

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

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

Brain Functions Can this be supported by evidence? Sperry’s experiment was A NATURAL EXPERIMENT 11 participants Sperry’s Ps were epileptics who could not be treated with drugs

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 1/10 th sec

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?

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

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

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)

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

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!!!

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

Has the right hemisphere the ability to process language?

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).

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.

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.

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.

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.

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

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

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

Role of each Hemisphere LeftRight Speech Production of speech, comprehension of the literal meaning of speech Emotional inflections, understanding jokes & humour, sarcasm, emotional content of speech

Role of each Hemisphere LeftRight 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

Role of each Hemisphere LeftRight Vision Details Overall configuration; spatial processing (e.g., arranging pieces of a puzzle or drawing a picture)

Role of each Hemisphere LeftRight Mode or Style (How data are processed) Details, parts, pieces Gestalt, overall configuration; global form

Role of each Hemisphere LeftRight 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?

Role of each Hemisphere LeftRight High spatial frequency Low spatial frequencies:

Role of each Hemisphere RightLeft High spatial frequency Low spatial frequencies:

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

EVALUATION & Criticism SEX DIFFERENCES Women have less lateralised brains Perhaps RIGHT HANDED male brains are more RIGHT <> LEFT specialised? KIMURA reported more aphasia in men who had left brain damage

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

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

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

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

The split brain procedure What do you think?

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?

Roger Sperry (1968) was given a NOBEL PRIZE for this research READ this study up THE END