Whether you are left-handed, right-handed or ambidextrous, “laterality” is part of our identity.
But many people don’t realize that we have other biases, too, that aren’t unique to humans. My colleagues and I have published a new study that shows that aligning our biases with those of others can have social benefits.
Across cultures, human populations have a high rate of right-handedness (about 90%). We also have a strong demographic bias in how we recognize faces and their emotions.
A large majority of the population recognizes identities and emotions more quickly and accurately when they are located in the left visual field than in the right visual field.
These types of biases develop in our brains from early childhood. The left and right hemispheres of the brain control motor action on opposite sides of the body. If your left visual field is dominant, it means that the right side of your brain takes over in recognizing faces and emotions.
Until recently, scientists thought that behavioral biases were specific to humans. But animal research over the past few decades shows that behavioral biases exist in every branch of the vertebrate tree of life.
For example, chicks that peck for food with one eye oriented are better at distinguishing grains from pebbles. Additionally, chicks that have one eye oriented to watch for predators are less likely to be eaten than non-lateralized chicks.
Studies show that animals exhibiting bias tend to perform better on survival-related tasks in laboratory experiments, which likely translates to better survival rates in the wild.
But the chicks that are most at an advantage are those that have one eye turned toward the ground (to find food) and the other toward the sky (to watch for threats). One advantage of the “split brain” is that wild animals can forage for food and watch for predators—an important multitasking ability.
So why do animals have behavioral biases?
Research suggests that brain hemispheric biases evolved because they allow both hemispheres of the brain to control different behaviors simultaneously. They also protect animals from confusion.
If both sides of the brain had equal control over critical functions, they could simultaneously order the body to perform incompatible responses.
Thus, biases free up certain resources or “neural capacities,” making animals more efficient at finding food and protecting themselves from predators.
Animal studies suggest that it is the presence, not the direction (left or right), of our biases that matters for performance. But this does not explain why so many people are right-handed on motor tasks and have a left visual field bias for processing faces.
Every person should have a fifty-fifty chance of being left- or right-handed. Yet in the animal kingdom, the majority of individuals in a species have the same orientation.
This suggests that aligning your biases with those of others in your group might have a social advantage. For example, animals that align with the population when engaging in cooperative behavior (grouping, herding) dilute the chance of being captured by a predator. The few that turn away from the group or school become obvious targets.
Although humans are strongly lateralized, regardless of ethnicity or geographic origin, there is still a significant minority in the population, suggesting that this alternative bias has its own merits.
The prevailing theory is that deviating from the population gives animals an advantage in competitive interactions, by creating an element of surprise. This could explain why left-handers are overrepresented in professional interactive sports such as cricket and baseball.
In the first study of its kind, scientists from the universities of Sussex, Oxford, Westminster, London (City, Birkbeck) and Kent put our human behavioural biases to the test.
We investigated associations between hand strength and performance, as well as direction of bias and social ability. We chose a behavior that is consistent with animal research.
More than 1,600 people of all ages and ethnicities participated in the survey.
People don’t always use their preferred hand: some people are slightly, moderately, or strongly left-handed. So we measured our participants’ left-handedness using a timed color-matching task on a pegboard.
Not everyone knows whether they have visual field bias, so we assessed this in participants using images of faces expressing different emotions (such as anger and surprise) presented on a screen.
People with light to moderate hand strength (left or right) placed more colored pegs correctly than those with strong or weak hand strength. These results suggest that in humans, extremes may limit our performance flexibility, unlike in wild animals.
The majority of participants exhibited a standard bias (right-handedness for motor tasks, left visual field bias for face processing). But this is not the case for everyone.
To test for associations between social skills and bias direction, participants were categorized into four groups based on their hand and visual side biases: standard (right hand, left visual), right-cluttered (right hand, right visual), left-cluttered (left hand, left visual), and reversed (left hand, right visual). They also completed a survey assessing their social difficulties.
The standard profile, found in 53% of participants, was not associated with a social advantage over the crowded left or right groups. In contrast, the relatively rare inverted profile (12%), was associated with significantly lower social scores compared to the other groups.
People in the reversed group were four times more likely to have a self-reported diagnosis of autism or attention deficit hyperactivity disorder (ADHD).
This study does not allow us to determine whether there is a causal relationship between the reversed profile and autism and ADHD. However, we plan to conduct research to determine whether skewed profiles can serve as an early risk marker for autism and ADHD in early childhood, which could pave the way for earlier screening and diagnosis and the development of new interventions.
This study reminds us that we humans have an evolutionary history, much of which we share with other animals. We need to study ourselves in the context of the animal kingdom if we are to truly understand our modern brains and behavior.
Gillian Forrester, Professor of Comparative Cognition, University of Sussex
This article is republished from The Conversation under a Creative Commons license. Read the original article.