Sperry (1968) split brain study

Sperry (1968) Split brain study

‘Hemisphere deconnection and unity in conscious awareness’

American Psychologist 23 pp723-33


introduction

• brain has 2 hemispheres

• connected by commissural fibres

• lateralisation of function – each has different functions – cognitive / motor

• split to treat extreme epilepsy



the studies: subjects

• 11 'most radical disconnection'

• 2 benefited; others 'recent'


designs: natural experiments

• variables occur 'naturally

• e.g. socio-economic- but in this case surgical procedures

• carefully controlled tests

• also case studies

• open ended interviews etc


procedure • one hand feeling unseen objects • attention to one ‘visual field’ • image shown for 1/10th sec (to prevent eyes

moving to prevent use of other visual field)• 2 images shown for 1/10th s; one to each field• etc


results: visual test 1

• subject show image in one visual field

• recognised if in that field before

• not recognised if re-shown in other field

Right visual fieldLeft visual field


results: visual test 2

• RH subjects shown objects in each field

• could describe object in R field

• said no object in L field, or ‘just a flash'

• able to respond non-verbally (pick up object with L hand) to object in L field


results: visual / drawing test

• 2 objects shown 1in LVF, 1RVF

• drew object with shielded L hand

• reported they had drawn object in R field!

When asked to say what they

had drawn they would name the object shown to their RVF (e.g.

banana)!

they could draw, with the left

hand, the object (e.g. pen) that

had been presented to their

LVF.


results: tactile test

• objects in R hand => verbal description

• object in L hand => only NV response

• L hand unable to respond to stimulus in R hand

When they felt and object with the right hand patients could

name the object

When they felt and object with

the left hand patients could

not name object(but could

identify it non-verbally, by picking it out from a group)

Patients would feel one object with each hand

Left hand could not respond to what the right

hand felt


results: 'competing tasks'

• R and L hand had different tasks

• could do both at same time

• non-split brain subjects slowed by this

• only useful for odd lab tasks!


discussion: Sperry’s conclusions

• apparent doubling of most areas of conscious awareness

• hemispheres appear unaware of each other

• easier to think of two hemispheres as two people


discussion: not a simple tale! • R side could (literally) tell L side what it

knew! • in lab had to be prevented from talking • = sides not so isolated • so personality / intelligence effects limited • some STM / concentration difficulties


discussion

• difficult to generalise!

• variation even between only 11 subjects

Education

Sperry (1968) split brain study