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Side-Dominant Science: Are You Left- or Right-Sided?

A sidedness selection from Science Buddies



George Resteck

Key concepts
Brain
Laterality
Handedness
Sidedness
Left/right dominance

Introduction
If you write with your right hand, you might also prefer to draw a picture, throw a ball or eat food with the same hand. But have you ever wondered if your right foot is also more dominant than your left foot? What about your right eye and ear—do you prefer to use them more than your left ones? In this activity you'll get to find out whether people have a sidedness—that is, whether they generally prefer to do most activities with one side of their body—and which side that is.

Background
Each person's brain is divided into two sides—the left and right hemispheres. In some cases, one hemisphere may be more active than the other during a certain activity. For example, when someone processes language, one hemisphere is usually more active than the other. Doing this or other activities, however, is not absolutely limited to using one hemisphere or the other, or even certain hemispheric parts. Different brain areas are important and work together for different activities, such as speech, hearing and sight. But if part of a hemisphere is damaged when a person is young, other parts of the brain can often take over doing whatever the damaged regions of the brain used to do.

What do the brain's hemispheres have to do with sidedness? When someone is processing language, one hemisphere is usually working harder than the other. There is also some correlation between the side(s) we use in our brain and the side we use on our body. This preference to use one side of the body over the other is known as sidedness, laterality or left/right dominance.

Materials
• Paper
• Pen or pencil
• A coin
• Paper towel tube or toilet paper tube
• A seashell or phone
• At least five volunteers

Preparation
• Have all of the materials ready so that you will be able to quickly test each volunteer.
• Prepare a small data table on a piece of paper to record your results. Going down the left side of the paper, write: "Hand," "Foot," "Eye" and "Ear." Going across the top of the paper, write your volunteers' names.

Procedure
• Ask your first volunteer to write their name on a piece of paper. Which hand do they write their name with? Record the result (writing either "Right" or "Left") in your data table in the row labeled "Hand," in the column under the volunteer's name.
• Place a coin on the floor directly in front of your first volunteer. Ask them to step onto the coin. Which foot is used to step on the coin? Record the result in your data table in the "Foot" row, under the volunteer's name.
• Give your first volunteer a paper towel tube or toilet paper tube and ask them to look at a distant object through it. Which eye do they use to look through the tube? Record the result in your data table in the "Eye" row, under the volunteer's name.
• Give your first volunteer a seashell or phone and ask them to listen to it. Which ear do they put the shell or phone up to? Record the result in your data table in the "Ear" column, under the volunteer's name.
• Repeat this process with at least four other volunteers. Be sure to record the results under the new volunteer's name each time.
Are more of your volunteers right-handed or left-handed? What about right-footed versus left-footed, right-eyed versus left-eyed and right-eared versus left-eared? What side is the most common overall?
How many people that are right-handed are also right-footed? (How about for lefties?) What about for the other possible combinations? Do you see a correlation?
Extra: In this activity you only used one test to check for dominance in your volunteer's hands, feet, eyes and ears. Using additional tests would help you check and confirm your results. Can you think of other ways to test for sidedness using objects from around your home? Using other tests, are the results the same as the ones you got doing the original activity?
Extra: If you collect additional data on your volunteers and test more volunteers, you can check your results and also test whether sidedness is linked to another factor. Does the trend in your results hold as you test more volunteers? Do you see a correlation between sidedness and other factors, like age, gender or being genetically related?
Extra: Sometimes sidedness can run in families. Try to find volunteers from different families and then group your results by family. Do different families have similar or different percentages?

Observations and results
Were more of your volunteers right-handed than left-handed? If a person was right-handed, did they usually also use their right foot, eye and ear?

You probably already know that most people are right-handed. In fact, roughly 70 to 90 percent of people are right-handed. From this activity, you probably saw that most people who are right-handed are also right-sided overall. That is, they mostly prefer to use their right foot, eye, and ear as well. But there are certainly exceptions, particularly with eyes and ears—a right-handed person may prefer using their right foot and right ear, but prefer their left eye over their right one. Similarly, a right-handed person may prefer their right foot and eye, but prefer their left ear. You may have seen a similar trend with left-handed people. Because the majority of people who are right-handed are also right-footed, in some cases where a person writes with their right hand but prefers to use their left foot, they may have been predisposed to being left-handed but were raised to use their right hand.

Overall, whereas the vast majority of the global population is right-handed, it's thought that a smaller percentage is right-footed, an even smaller percentage is right-eyed, and yet an even smaller percentage is right-eared (perhaps a little over half), but this trend is unlikely to be visible using only five volunteers. Why might people have a weaker preference for an eye or ear that matches their dominant side? Perhaps one ear or eye is stronger than the other.

More to explore
Neuroscience for Kids, from Eric H. Chudler, University of Washington in Seattle
Science Experiments for Kids: Test Your Dominant Side, from Science Kids
What Does Handedness Have to Do with Brain Lateralization?, from M. K. Holder, Indiana University Bloomington
Are You Left- or Right-Sided?, from Science Buddies



 

This activity brought to you in partnership with Science Buddies

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