Sperry - Split brain research

Aim

To investigate the extent to which the two hemispheres are specialised for different functions.

Procedure

Participants focused on a fixed point in the centre of a screen. Stimuli were flashed for less than 0.1 seconds, preventing eye movements.

• Information presented to the left visual field was received only by the right hemisphere.
  Information presented to the right visual field was received only by the left hemisphere.

Because the corpus callosum had been cut, information could not pass between the hemispheres.

Tasks included:
Recognising words and pictures.
Identifying objects by touch.
Drawing images with either hand.

Visual tasks - findings

When an object was presented to the right visual field (left hemisphere), participants could describe it verbally.

Information presented to the left visual field (right hemisphere) could not be described verbally. Participants often reported seeing nothing. However, they could point to or select the correct object with their left hand. For example, if the word “KEY” was shown to the left visual field: Participant could not say “key”. But could select a key from a collection of objects with the left hand.

Tactile tasks - findings

When an object was placed in the left hand (right hemisphere) where the participant could not see the object, participants could not name it but could identify it by touch or pointing it out from a selection of images.

Drawing tasks - findings

Participants could draw objects presented to the right hemisphere with their left hand. They could also draw objects presented to their left hemisphere with their right hand.

Conclusion

Sperry demonstrated that the cerebral hemispheres are functionally specialised. The left hemisphere appears dominant for language production and verbal processing, whereas the right hemisphere is dominant for visuospatial skills and certain non-verbal functions. The findings provide strong evidence for hemispheric lateralisation.

Evaluation of Split-Brain Research

Strength: Controlled Scientific Research

Sperry used highly controlled laboratory procedures. This increased internal validity because researchers could be confident that differences in performance were due to hemisphere specialisation.

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Strength: Useful Evidence for Lateralisation

The research demonstrated that the two hemispheres have specialised functions. It significantly improved our understanding of brain organisation.

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Limitation: Small and Unusual Sample

Only 11 split-brain patients were studied. These individuals had severe epilepsy and had undergone major surgery, making them unrepresentative of the general population. This limits generalisability.

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Limitation: Low Ecological Validity

The tasks involved artificial laboratory procedures, such as briefly presenting images to one visual field. These tasks may not reflect how the hemispheres operate in everyday life.

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Limitation: Plasticity May Affect Findings

The brains of split-brain patients may adapt after surgery. Therefore, the findings may not fully represent the functioning of a normal brain.