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hemispheric lateralisation - Coggle Diagram
hemispheric lateralisation
Sperry's Research Procedure
Sperry used a tachistoscope to present visual stimuli to the participants.
The tachistoscope has a focal point in the middle and two areas where stimuli was presented. The participants using the tachistoscope would have one eye covered and were instructed to stare at the focal point.
Information presented to the left of the focal point would be seen in the left visual field which would then travel to the right hemisphere. Information presented to the right of the focal point would then travel to the left hemisphere.
All visual stimuli was presented for only 0.1 seconds. This was a control as it is too quick for eye movements to cause visual information to enter both visual fields.
Wearing an eye patch and staring at the focal point were controls. These controls ensure that stimuli was presented only to the desired visual field.
research to support
Split Brain Research (Sperry, 1968)
• Sperry (1968) used a quasi experiment in a laboratory with an independent measures design.
• The independent variable was whether the individual had a split-brain or not.
• There were dependent variable was that individual’s performance on visual and tactile tasks.
functions of the hemispheres
Language is localised in the left hemisphere
Corpus Collosum – bundle of nerve fibres that connect the right and left hemisphere
counterlateralisation - opposite sides of the brain control opposite sides of the body (muscles and sensory information)
Left Hemisphere – logic, maths, facts
Right hemisphere – creativity, imagination
Sperry's Research Results:
• Information presented to the right visual field (processed in left hemisphere) could be described in speech and writing (with the right hand).
• If the same information is presented to the left visual field (right hemisphere), the participant insisted he either did not see anything or that there was only a flash of light on the left side; the information could not be described in speech or writing.
• However the participant could point with his left hand (controlled by the right hemisphere) to a matching picture / object presented among a collection of pictures / objects.
• Participants would only recognise stimuli if the stimuli was presented again to the same visual field. If participants were shown stimuli in the right visual field, but then shown the same stimuli to the left visual field, they would claim to have not seen it before.
what is lateralisation?
Lateralisation is the idea that the two halves of the brain are functionally different and that each hemisphere has functional specialisations, e.g. the left is dominant for language, and the right excels at visual motor tasks.
The two hemispheres are connected through nerve fibres called the corpus callosum, which facilitate interhemispheric communication: allowing the left and right hemispheres to ‘talk to’ one another.
evaluation
Strengths
– Quasi study – as there was no manipulation by the experimenter, establishing cause and effect becomes more difficult than a traditional experiment.
Ethics – as the study used a quasi methodology, Sperry did not need to manipulate anything, which is more ethical than studies which manipulate variables.
Limitations
The external validity in this study may be considered low because the stimuli was selectively delivered to one hemisphere. This does not happen in real life and thus is not representative of the everyday experience of ‘split-brain’ patients.
No control group, Sperry did not use a control group, which makes it difficult to truly establish cause and effect. However, it is important to note that in this study a control group was not needed as the results of the tasks for people without split corpus callosums were already known.