Introduction to Lateralisation
Welcome! In this chapter, we are going to explore one of the most fascinating parts of the brain: the fact that it is split into two halves. Even though your brain looks like a symmetrical walnut, the two sides (called hemispheres) actually have different "specialties." This is known as lateralisation of function.
Think of it like a professional kitchen. You have a chef who specializes in pastry and another who specializes in sauces. They are in the same kitchen and work together, but they have very different jobs! Understanding this helps us see how our brain manages so many complex tasks at once.
What is Lateralisation?
Lateralisation refers to the idea that the two halves of the brain are not exactly the same. Each hemisphere has specific roles that the other side might not do as well. This leads to something called asymmetrical function.
Asymmetrical function simply means that the two sides of the brain are "not balanced" or "unequal" in terms of what they control. One side might take the lead on talking, while the other takes the lead on drawing.
The Role of the Corpus Callosum
If the brain is split into two halves, how do they talk to each other? That is where the corpus callosum comes in.
The corpus callosum is a thick bundle of nerve fibers that acts like a bridge or a high-speed "data cable" connecting the left and right hemispheres. It allows messages to be sent back and forth constantly so that your brain can act as one single unit.
Note: To see what happens when this bridge is "cut," you can look at the Sperry (1968) study in the next chapter!
The "Personalities" of the Hemispheres
While the two sides usually work together, they do have preferred "hobbies" or functions:
The Left Hemisphere
For most people, the left side of the brain is the "logical" side. Its main roles include:
• Language: This is a big one! The left side usually handles speaking, reading, and writing.
• Logic and Analysis: Dealing with numbers, facts, and step-by-step thinking.
• Control of the right side: The left hemisphere controls the movements of the right side of your body.
The Right Hemisphere
The right side is often seen as the "creative" or "spatial" side. Its main roles include:
• Spatial Awareness: Helping you navigate a room or understand maps.
• Recognizing Faces: Helping you tell your friends apart.
• Creativity and Music: Processing emotions and artistic expression.
• Control of the left side: The right hemisphere controls the movements of the left side of your body.
Quick Memory Trick:
Left = Language and Logic.
Right = Recognizing faces and Reading maps (Spatial).
Key Takeaway: Lateralisation means the brain's functions are divided. The left focuses on language/logic, and the right focuses on spatial/creative tasks, with the corpus callosum connecting them.
Lateralisation and Sex Differences
Psychologists have wondered if the "amount" of lateralisation explains why males and females sometimes perform differently on certain tasks. This theory suggests that male and female brains are "wired" slightly differently.
The Theory:
• Males are thought to be more lateralised. This means their brain functions are strictly divided into one side or the other. This is often used to explain why males might be stronger at specific spatial tasks (like map reading).
• Females are thought to be less lateralised (more bilateral). This means they may use both hemispheres for the same task, like language. This is often used to explain why females might be stronger at language-based tasks.
Evaluating the Sex Differences Explanation
Don't worry if this seems a bit "stereotypical"—psychologists evaluate this theory by looking at its strengths and weaknesses.
Strengths:
• Scientific Evidence: Some brain-scanning research has shown that when performing language tasks, women often show activity in both hemispheres, while men show activity mainly in the left.
• Supporting Studies: Research into brain damage often shows that if a woman has a stroke in the left hemisphere, she is less likely to lose all her language skills than a man, because she might be using her right hemisphere for language too.
Weaknesses:
• Small Differences: Many studies find that the differences between male and female brains are actually very small. Most of us use our brains in very similar ways.
• Effect of Environment: The theory might ignore nurture. Maybe boys are encouraged to play with spatial toys (like LEGO) and girls are encouraged to talk more, which develops the brain differently. It might not be "built-in" from birth.
• Contradictory Results: Not all studies show these differences. Some researchers argue that there is more variation between two individual men than there is between "the average man" and "the average woman."
Did you know? This debate links back to the Nature vs. Nurture debate you will see in other parts of the course!
Quick Review Box
1. What is the corpus callosum? The bundle of fibers connecting the two hemispheres.
2. Which hemisphere usually handles language? The left hemisphere.
3. What does "asymmetrical function" mean? That the two sides of the brain do different things.
4. What is a weakness of the sex differences theory? Differences found are often very small and might be caused by how we are raised (environment) rather than just biology.
Key Takeaway: While there is some evidence that male brains are more lateralised than female brains, it is a controversial area of psychology with plenty of arguments on both sides.