Lateralisation

Hemispheric Lateralisation

Hemispheric lateralisation refers to the brain and hemispheres. We can define hemispheric lateralisation as:

The brain has two hemispheres, the right and left, connected by the corpus callosum (a thick mass of around 300 million nerve fibres), allowing them to communicate. Certain functions are localised to the hemispheres, and either hemisphere may perform more efficiently with different processes when compared to the other.

Lateralisation Psychology: The Role of the Hemispheres

As we mentioned above, the corpus callosum connects the left and right hemispheres and allows them to communicate. When we sever the corpus callosum and disrupt the connection, the brain cannot share information from one hemisphere to another.

The Role of the Left Hemisphere

The left hemisphere is involved in controlling the right side of the body, although both hemispheres constantly communicate with one another to ensure information is processed correctly. Pinpointing the exact locations of functions is difficult, but we can generally estimate where functions are occurring based on neuroimaging techniques.

The role of the left hemisphere includes:

• Controlling the movement on the right side of the body (the left motor cortex controls the right hand, leg, and other bodily movements made on the right side of the body).
• Broca's area is responsible for speech production in the left hemisphere, and Wernicke's area is responsible for speech comprehension; therefore, the left hemisphere specialises in language;
  • When you talk, Broca's area is hard at work to produce speech, and when damaged, it results in Broca's aphasia, an inability to speak properly.
  • When you speak to a friend, understanding what they are saying involves Wernicke's area. When damaged, it results in Wernicke's aphasia, an inability to understand or comprehend speech.
• Logical processing, such as analysing writing, reading, and making calculations
  • Research suggests brain hemispheres can be dominant, for example, which hand you prefer to complete actions (left-handed versus right-handed).
  • People tend to be right-handed, and a long time ago, those who were left-handed were viewed with suspicion. Attempting to switch handedness didn't always go well, but language is a uniquely human skill and being right-handed when writing alludes to the left hemisphere's dominance in language.
• Memory association formation, alongside paying attention to specific information.
• Expressions focused more so on positive emotions and perceiving positive emotional behaviour in others.

The Role of the Right Hemisphere

The right hemisphere controls the left side of the body, the opposite of the left hemisphere. It also specialises in certain functions; the role of the right hemisphere includes:

• Controlling the movement on the left side of the body (the right motor cortex controls the left hand, leg, and other bodily movements on the left side of the body).
• Visual and acoustic processing (interestingly, this also includes musical proficiency; our ability to hear pitch, melody and the different intonations involved in speech and conversation, as well as the music we hear, alludes to why many refer to the right hemisphere as the creative hemisphere).
• Emotional regulation and the perception of negative emotions and behaviours in others.
• Recognition of faces.
• Spatial awareness; the right hemisphere specialises in spatial tasks.

The hemispheres of the brain differ in structure and function, brain infographic vector created by freepik - www.freepik.com.

Lateralisation Psychology Evaluation

Now that we know what lateralisation is in psychology and the roles of the hemispheres, we can evaluate the strengths and weaknesses of lateralisation as an explanation of sex differences between males and females. Physical differences exist between males and females, which can allude to distinctions between the behaviour of the sexes and cognitive function and ability.

• When we examine the brain and the differences between sexes, females show less brain lateralisation for language skills, suggesting they are better at processing and performing language feats than males. They show more bilateral activity (on both sides) for language skills.

• Males, however, show greater lateralisation when considering their language skills, and it is suggested that males are better at performing spatial tasks and activities. They use one hemisphere more dominantly than the other.
• Sperry (1968) highlights how severing the corpus callosum demonstrates evidence for lateralisation of function.

Strengths of Lateralisation in Psychology

Let's explore some of the supporting evidence for differences in the sexes.

• According to Ardekani et al. (2013), females have a larger corpus callosum than males on average, when controlling for potential confounding variables that may affect the ratio measurement. A thicker corpus callosum suggests why their bilateral activity is occurring so efficiently.
• Rilea et al. (2005) examined sex differences in spatial tasks, specifically lateralisation and dominance of the right hemisphere. The preceding theory was that males should have an advantage in spatial tasks, shown by how right-hemisphere dependent the task is
  • They found some advantages for males: the mental rotation task showed males had right-hemisphere advantages, whereas women showed no hemisphere difference, but sex differences were non-existent. However, men performed better than women in the water level task, with both sexes showing right-hemisphere advantages. Although not as pronounced, the study shows how males tend to show right-hemisphere dominance in spatial tasks.

Weakness of Lateralisation in Psychology

Let's explore the research that disputes the lateralisation differences in sexes.

• First, we can highlight how Rilea et al. (2005) found no significant sex differences in all investigated categories. More often than not, there were no sex differences rather than the presence of sex differences in lateralisation. This demonstrates how the dominant hemispheres are not as profound as once thought.
• According to research by Ardekani et al. (2013), smaller brains have a larger corpus callosum, regardless of gender differences. Although they controlled for this by collecting two groups of males and females with matching brain sizes, other research on brain size and sex differences needs to consider potential confounding variables.
• Daphna et al. (2015) examined the MRI (magnetic resonance imaging) scans of male and female brains to establish if distinct features that could be labelled male or female-specific could be identified. Daphna et al. (2015) highlighted how, whilst genital differences exist, after analysing 1,400 brains, there are minor sex/gender differences in the brain in terms of features, but this does not warrant a distinction between male brain and female brains, suggesting they are more similar than they are different.