A01 Split-Brain Research Into Hemispheric Lateralisation

• Hesmispheric lateralisation


  Language is subjected to the left hemisphere and therefore is subject to hesmispheric lateralisation. This led to Sperry et al to do split-brain research to see if other neural processes may be organised this way.
• Sperry et al study

  Invited a unique group of individuals all of whom had undergone the same surgicial procedure, commissurotomy, where the corpus callosum and other tissues that connect the two hemispheres were cut in the middle to separate them.
• Consequence of the commissurotomy


  Therefore, the main communication line between the two hemispheres was removed and allowed to see extent to which the two hemispheres were specialised for certain functions and whether the hemispheres performs tasks independently of one another.
• Sperry et al study procedure

  Devised a general procedure where an image/word could be projected to an individual's right visual field (which is processed by the left hemisphere) and the same or different word could be projected to the left visual field (which is processed by the right hemisphere). Due to the split-btrain in the patients, information could not be conveyed from one hemisphere to the other.
• Findings - describing what you see

  When picture shown to right visual field (left hemisphere) the ppt could easily describe what was seen. But when the same object was shown to let visual field (right hemisphere), the ppts couldn't describe it.
• Exlanation for Sperry's findings

  Ppts inability to describe objects in the left visual field was because of the lack of language centres in the right hemisphere. In the normal brain, messages from the right hemisphere would be relayed to the language centres in the left hemisphere.
• Recognition by touch


  Although the ppts couldn't attach verbal labels to objects projected in left visual field, they were able to select a matching object from a grab-bag of different objects, using their left hand (which is linked to the right hemisphere).

  The objects were placed behind a screen so as not to be seen.
• Further function of left hand (Recognition by touch)

  Left hand was also able to select object most closely associated with object presented in the left visual field. Ppts were not able to verbally identify but could still understand what the object was using the right hemisphere and select the corresponding object accordingly.
• Composite words


  If two words were presented simultaneously, one on either side of the visual field (for example, a key on the left and a ring on the right), patients would write with their left hand the word key (left visual field goes to the right hemisphere linked to left hand) and say the word ring. Shows the superiority of the right hemisphere in terms of drawing.
• Matching pairs


  The right hemisphere apperas dominant in terms of recognising faces. When asked to match a face from a series of other faces, the picture processed by the right hemisphere was consistently selected whilst the left hemisphere was consistently ignored.
• Composite pictures


  When a composite picture of two different halve-faces was presented, the left hemisphere dominated in terms of verbal descripation whilst the right hemipshere dominated in terms of selecting a matching picture.