Lateralisation

• What is the definition of lateralisation? the idea that 2 halves of the brain are functionally different and certain processes, activities or behaviours are controlled by one hemisphere.
• What is the definition of hemispheric lateralisation? The 2 hemispheres of the brain are functionally different
• What is the right hemisphere and what is its function? The right side of the brain processes info from the left half of the body (e.g. visual info from the left eye). Its function is face recognition (and emotions on face), drawing ability and spatial tasks.
• What is the left hemisphere and what is its function? The left side of the brain processes information from the right half of the body (e.g. visual info from the right eye). Its function is language (localised and lateralised).
• Who are the split brain patients? A unique group of patients who had a corpus callosotomy - where the corpus callosum is severed so that the two hemispheres are separated and don't communicate with each other. This was done to control frequent and severe eplieptic fits.
• Who was the key researcher for lateralisation?

  Sperry (1968)
• What was the aim of Sperry's study? To investigate what functions of the brain are lateralised.
• What was the procedure of Sperry's study? Compared split brain patients to others with no hemisphere separation. Different activities were tried with the patients including touch of objects and visual presentation of stimuli to see how the different sides perform on tasks. (visual and tactile tasks)
• What are visual tasks? A word or picture is projected into the left or right visual field and the patient will be asked something about that stimuli.
• What are tactile tasks? Tactile tasks (tasks with objects) were carried out with the p's hands underneath a screen so the p's couldn't see what they were doing. They had to use 'feel' only.
• What were the findings of Sperry's study when describing what they had seen in visual field? - if a picture was shown to the left visual field, they could not describe it (often reported that there was nothing there) e.g. can't see pen.

  - if the picture was shown to the right visual field, they could easily describe the picture shown to their right visual field e.g. apple.
• What were the findings of Sperry's study for recognition by touch? - If the object was shown to the left visual field, they would be able to select the object because it was 'seen' by the right hemisphere, and the left hand is also controlled by the right hemisphere (but they couldn't say anything about the object).

  - If two different objects were placed into each hand the left hand would pick up the right object.
• What was the findings for Sperry's study - drawing? The drawings were consistently better when drawn by the left hand (controlled by right hemisphere). This reveals that the right hemisphere (and therefore the left hand) has superior drawing ability.
• What were the findings for Sperry's study - composite words? If a patient was shown two different words to their left and right visual field, they would say ring as it is processed by the left hemisphere and they would pick up the key (processed by right hemisphere)
• What were the findings of Sperry's study - face recognition? When shown an image of a person (left half woman and right half man) as the left hemisphere deals with language, the person would be likely to say "man". If the split brain patient was asked to pick out a matching photo, as the right hemisphere deals with face recognition, they are more likely to select and image of the woman.
• What were the conclusions of Sperry's study? - It seems that in these patients, the hemispheres of the brain process information separately.

  - Hemispheres do have differing functions (e.g. language left and drawing ability right)

  - P's seem to have two separate streams of consciousness with their own memories and perceptions.
• Evaluation of Sperry's study: + The study is a quasi experiment in controlled conditions = standardised procedures so good internal validity, however lack of ecological validity

  + Light was flashed very quickly (1/10th of a second) - didn't have time to move their eye across the image to process it

  - low population validity (only 11 patients, and they were epileptic patients)
• Strength of lateralisation - advantages to having a lateralised brain: P - It is generally assumed that there are advanatages to having a lateralised brain.

  E - It increases neural capacity by using one hemisphere to engage in a particular task leaving the other one free to engage in another function. In chickens, brain lateralisation was associated with enhanced abilities to find food and stay vigilant for predators at the same time. (Rogers et al)

  E - provides evidence that brain lateralisation enhances brain efficiency in cognitive tasks that demand the simultaneous but different use of both hemispheres

  H- this study uses animals - ethics? also low population validity so inappropriate to generalise the findings to humans.
• Limitation of lateralisation - disadvantages to having a lateralised brain: P - There are also a number of disadvantages associated to having a lateralised brain.

  E - There is a link between lateralisation and the immune system, in that being left handed is linked with poorer immunity (Tonnessson et al)

  E - This suggests that they same genetic processes that lead to lateralisation may also affect the development of the immune system.
• Strength of lateralisation - can change over time: P - There is research to support that lateralisation can actually change over time

  E - Szaflarski et al (2006) found that language became more lateralised to the left hemisphere with increasing age in children and adolescents., but after the age of 25, lateralisation actually decreased with each decade of life.

  E - this supports that age can be a factor that can affect lateralisation of the brain. One possibility is that using the extra processing resources of the other hemisphere may in some way compensate for age - related declines in function - lateralised brain only a feature for young adults and not the case for everyone.
• Limitation of lateralisation - disputed evidence: P - some of the early claims about lateralisation have been disputed with evidence.

  E - Gazzangia (1998) suggests that some of the early discoveries from split-brain patients have been disconformed by more recent studies. JW developed the capacity to speak out of the right hemisphere and can now speak if info is presented to the left or right brain.