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?

AS level Psychology

The Core studies

AS level Psychology

The Core studies

The Split Brain Studies - R Sperry 1968 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….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 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 FunctionsBrain 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 FunctionsBrain 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 procedureThe 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


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?


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


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


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)


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


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!!!


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.


Conclusion

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


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


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 HemisphereLeft Right Speech Production of

speech, comprehension of the literal meaning of speech

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

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

Role of each HemisphereLeft Right Vision

Details

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

Role of each HemisphereLeft Right Mode or Style

(How data are processed)

Details, parts, pieces

Gestalt, overall

configuration; global form

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?

Role of each HemisphereLeft Right

High spatial frequency

Low spatial frequencies:

Role of each HemisphereRight Left

High spatial frequency

Low spatial frequencies:

EVALUATION & CriticismEVALUATION & Criticism

The Ps were epileptic - CAN they be said to represent NORMAL

brains?

INDIVIDUAL DIFFERENCES - some people have more lateralised brains


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


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


Do the two halves of the brain represent two minds?

Evidence Hemispherectomy - the removal of

one half of the brain….. the SELF remained


SPERRY said…

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


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


What do you think?

SPERRY - QUESTIONSSPERRY - 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 researchRoger Sperry (1968) was given a NOBEL PRIZE for this research

READ this study up THE END

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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?