Hemispheric lateralisation and split-brain research

Question 1

Describe language functions.

Answer 1

Localised AND lateralised

• Language is left hemisphere only – analyser
• The right hemisphere contributes to the emotional context of what is being said – synthesiser

Question 2

Describe motor functions.

Answer 2

Motor functions
localised NOT lateralised
- Cross wiring occurs in the motor area – this is called
- Contralateral (opposite sides)

Question 3

Describe visual functions.

Answer 3

Visual functions
localised AND lateralised
- LVF – processed in the right hemisphere
- RVF- processed in the left hemisphere
- Vision is contralateral (opposite sides) but also ipsilateral (same sides)

Question 4

Evaluate.

Answer 4

+ Research support: Fink et al used PET scans and found that when people a neurotypical brain completed a visual task the right hemisphere was more active/dominant for global elements (e.g., a forest) but the left hemisphere was more active/dominant for finer detail e.g. specific trees).

-Contradictory research: Nielsen et al analysed brain scans of over 1000 people (aged 7-29 years) and found people used different hemispheres for different tasks but no evidence of a dominant side.

+Research support: Lateralisation is adaptive as can lead to two tasks being performed better. Research showed lateralised chickens could find food whilst watching for predators.

• Counterpoint: Neuroplasticity is adaptive as after trauma shows functions can be adaptive and taken over by non-specialised areas in the right hemisphere.

Question 5

Outline Sperry’s split-brain research.

Answer 5

11 participants who were epileptics and had their corpus callosum split.
Procedure:
Drawing task:
- Word/image is projected to the left visual field and participant has to draw what they saw. PPs drew but could not say the word/image.
Visual task
-Word/ image is projected onto right visual field and participant is asked to describe what they saw. PPs could describe image.
Conclusions:
- The left hemisphere is dominant in terms of speech and language.
- The right hemisphere is dominant in terms of visual-motor tasks.

Question 6

Evaluate.

Answer 6

+ Case study: Kim Peek had an amazing memory for dates which suggests semantic memory could be lateralised.

• Counterpoint: Kim Peek was born WITHOUT a corpus callosum. He could read from both pages of a book. This suggests he had two language centres.
• Sperry’s research was not compared to a neurotypical control group therefore the differences could have been due to the confounding variable of epilepsy.
  + Counterpoint: Research with control group supports the idea that the left hemisphere and right hemisphere are distinct. The split brain patients were faster at odd one out tasks.