Biopsychology : Hemispheric Lateralisation Flashcards
What does hemispheric laterlisation mean?
Two hemispheres of the brain are functionally different and certain mental processes and behaviours are mainly controlled by one hemisphere rather than the other.
What does the right hemisphere process?
info from the left side of the body
What does the left hemisphere process?
info from the right side of the body
Whats split-brain research?
A series of studies that began in the 1960s, where epileptic patients who had experienced a surgical separation of the hemispheres of the brain. This allowed researchers to investigate the extent to which brain function is lateralised.
What is the nasal retina?
The inner part of your eyes (closest to nose)
Whats the temporal retina?
The outer part of your eyes (sides)
What’s the optic chiasm?
The part where the visual fields cross over
What is the corpus callosum
Where the info is combined – when it reaches the cortex
What does the left visual field project info to?
Left eye: nasal retina
Right eye: temporal retina
What does the right visual field project info to?
Left eye: nasal retina
Right eye: temporal retina
Where does info from the nasal retina go?
Info from the nasal retina crosses to contralateral hemisphere (opposite side) at the optic chiasm
Where does info from the temporal retina go?
Info from the temporal retina does not cross, so remains in the ipsilateral hemisphere (same side)
What happens to visual info if the corpus callosum is severed?
The info arriving at the context cannot be exchanged between hemispheres, each hemisphere will only be aware if the contralateral info
Who did split brain patient experiments plus what did they find?
Roger Sperry (1960s) found that…
The left hemisphere - language
The right hemisphere – processing faces and facial emotion
What do we mean by ‘split-brain’ patients?
people who have two separated hemispheres of their brain (left and right), occurred because of serious epilepsy.
What operation is considered to cure epilepsy?
Commisurotomy – cuts callosum so the electrical discharge of epilespy cant move across the whole brain. So, the main communication line between the two hemispheres was removed
Sperry’s (1969) split brain experiment - Background
he realised that split-brain patient who’d undergone a commissurotomy could be studied to independently probe the function of the 2 hemispheres.
Sperry’s (1969) split brain experiment - Aim
to examine the extent to which the two hemispheres are specially for certain functions
Sperry’s (1969) split brain experiment - Procedure
The divided field → Ps looked ahead at a dot in the centre of the screen and see one item to the left (of their visual field/ peripheral vision) and then one item to the right for 0.2 seconds (to prevent subjects fro movement their eyes and transferring info between visual fields)
In a normal brain, the corpus callosum would immediately share the info between both hemispheres giving a complete picture of the visual world. However resenting the image to one hemisphere through only one visual fields of a split barn patient meant tat the info could not be conveyed from that hemisphere to the other.
Sperry’s (1969) split brain experiment - Findings
found that Ps could say what he’d seen on the right side but said they ‘didn’t see anything.’ on the left. When asked to close their eyes and draw what they’d seen with their left hand, they thought they were drawing that they’d read in their left eye but were actually drawing what the ‘didn’t see’ in their left eye
Sperry’s (1969) split brain experiment - Conclusion
when seen on the left side, P could answer what they’d seen because the right vision info goes to the left hemisphere which is responsible for language. When seen in the left eye, info went to the right hemisphere which is responsible for processing faces and facial emotion (visual) but couldn’t communicate with the left hemisphere due to the corpus callosum being damaged. Therefore, they are unable to speak of what they saw and its almost as if they hadn’t seen anything.
But, when asked to draw with their left hand, controlled by the right hemisphere, they were able to draw what they ‘hadn’t seen’ because the right hemisphere had seen the info but just hadn’t been able to express that it had. They will draw whatever was seen in the left eye whether they wanted to or wanted to draw what they’d seen in the right eye
Strengths of hemispheric lateralisation
• Support from more recent studies → Luck et al (1989) showed that split brain patients are faster than normal (controls) at identifying the odd one out in an array of similar objects, huge lighting the specialised processing abilities of the hemispheres. Kingston’s et al (1995) suggests that in the normal brain, the superior processing abilities of the left hemisphere are ‘watered doiwn’ by the inferior right hemisphere.
Limitations of hemispheric lateralisation
• Methodological issues that impact generalisability and interval validity → the study was a quasi experiment so Ps weren’t randomised to groups, introducing a potential bias. Only individuals w severe epilepsy that needed surgery were in the experimental group while the control were healthy people majority without epilepsy. Furthermore, the sample size is 11 so population validity is a concern. This means you must generalise with caution to the general public.
• Opposite findings → Gassaniga (1998), and more recent studies such as the case study of JW (had left hemisphere removed due to epilespy and had fairly normal speech by 17) show that the brain is able to adapt and the oversimplification of the hemispheric lateralisation may not be correct.
• Lateralisation may dismish with age → Szaflarski et al (2006) found that lang functions because inc lateralised to the left hemisphere during childhood, but it reverses after the age of 25, suggesting split brain research is not applicable to all ages.
• Contributed to pop psych → Nielsen et al (2013) analsyed brain scans from over 1000 people and found evidence of lateralisation but no support for the idea of a dominant side of the brain (the “artist’s brain”)
