Bilateral transfer

Bilateral transfer refers to the ability to learn to perform a task or skill with the opposite limb from the one that initially learned it. Learning the skill with the second limb is easier than learning it with the first limb because some of the learning has transferred to the second limb. While the limb in question is very often a hand or arm, bilateral transfer can also happen with lower limbs; this aspect has specific applications for athletes and those who suffer injuries to one limb. Researchers have determined that practicing a task or skill with one limb will help a person's ability to perform the task with the opposite limb and that this type of information transfer is stronger than imagining doing the task with the second limb. While the amount of learning that can be transferred is limited by such factors as side dominance and speed versus accuracy, bilateral transfer can still be helpful in learning and reinforcing some skills.

Background

The word bilateral is made up of two Latin words: bi, meaning "two," and lateralis, meaning "belonging to the side." Bilateral body parts are, therefore, those that come in pairs and have a matching or corresponding part on the opposite side of the body, such as the eyes, ears, arms, hands, legs, and feet. Researchers at Yale University first observed the ability of a part on one side of the body to more easily learn a task after the other side had already learned it about 1800. However, it was not until the 1950s that scientists began to understand how this bilateral transfer of information occurred. Researchers had theorized that a transfer of information took place in the brain. They conducted experiments on monkeys and other animals to attempt to understand where and how it happened.

Ronald Myers, a University of Chicago graduate student working with noted neuropsychologist and neurobiologist Roger Sperry, followed up on some of the earlier experiments. He taught cats to touch an image of a circle when it appeared on a screen in front of them, but he did it with one of the cat's eyes covered. When he later had the cats perform the task with the opposite eye covered, he found the cats still knew to touch the circles when they appeared. He had demonstrated that a skill learned on one side of the body could transfer to the other.

Myers then attempted to teach the same skill to another cat after severing its corpus callosum. The corpus callosum, which means "tough body" in Latin, is a thick bundle of nerves that connects the right hemisphere, or side, of the brain with the left. The right hemisphere of the brain controls the action on the left side of the body, while the left hemisphere controls the functions of the right side. The corpus callosum serves as an information conduit between the two. Myers performed surgery to ensure the left eye was only connected to the left hemisphere of the brain and the right eye was only connected to the right hemisphere.

Myers discovered that while the cat with the severed corpus callosum could learn to touch the circles with one eye, it had to learn the task again when Myers covered that eye and uncovered the other. His experiment documented that the transfer of learning from one side of the body to the other occurs through the corpus callosum. His experiment also showed that one side of the body could benefit from training in a skill or task received by the other side.

Overview

In the years since Myers conducted his experiments, researchers have determined that this transfer of learning occurs with other body parts as well. The ability has specifically been noted in the limbs as researchers have devised experiments that show that teaching one side of the body to perform a task, such as typing keys on a keyboard in a specific sequence, allows the other side of the body to master the task more quickly.

It has also been noted that this bilateral transfer takes place regardless of whether the limb in question is on the user's dominant or non-dominant side. Known as lateral dominance, this tendency to be right-handed or left-handed does impact bilateral transfer to the extent that the dominant side will learn the skill or task more easily and more proficiently, at least at first. However, even the non-dominant side will learn the task more readily when it has already been mastered by the dominant side. Bilateral transfer also occurs with those who are ambidextrous, or equally able to perform a task with either hand or leg.

The concept of bilateral transfer, also known as cross-education or intermanual transfer, is of particular interest in the world of sports. It has been shown that once an athlete learns a skill with one limb, it is easier to learn the task using the opposite limb. For instance, kicking a football or soccer ball involves a specific set of techniques to enable the kicker to control the distance and direction the ball will travel. Once the kicker has learned the necessary techniques with one foot, usually the dominant foot, it is much easier to master the technique with the other foot as well.

Medical researchers are also interested in bilateral transfer because of the potential for helping those with an impairment that affects one side of the body to recover function in the impaired part. Research has been conducted that indicates that practicing an activity with the non-impaired side of the body helps the impaired side as well. As muscles and nerves master the movements needed to perform a function, such as grasping an object, the muscles and nerves on the other side develop the same memory of the function, researchers believe. In some instances, these opposite muscles and nerves may eventually be able to perform the same function. This research is being applied to recovery from major medial episodes, such as stroke.

Researchers are also investigating the function of imagery in bilateral transfer. When test subjects are asked to imagine performing a function with one side of the body, both sides of the body seem to be able to more readily complete the task when asked to physically perform it. For instance, test subjects asked to imagine typing keyboard keys in a certain order with their dominant hand were also able to type the keys in order with their non-dominant hand, even though neither hand had practiced the task. Researchers have noted differences in speed and accuracy; however, they are able to conclude that bilateral transfer of learning can occur either through real or imagined experience.

Bibliography

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Land, William M., et al. "Effects of Physical Practice and Imagery Practice on Bilateral Transfer in Learning a Sequential Tapping Task." PLOS ONE, vol. 11, no. 4, 2016, p. e0152228, doi.org/10.1371/journal.pone.0152228. Accessed 16 Dec. 2024.

Mota, Deise M., et al. "Bilateral Transfer of Performance between Real and Non-Immersive Virtual Environments in Post-Stroke Individuals: A Cross-Sectional Study." International Journal of Environmental Research and Public Health, vol. 20, no. 4, 2023, p. 3301, doi.org/10.3390/ijerph20043301. Accessed 16 Dec. 2024.

Muller, K. et al. "Effects of Force Level and Hand Dominance on Bilateral Transfer of a Fine Motor Skill." University of Texas, 2016, repositories.lib.utexas.edu/items/7d05b0b6-cf39-41d4-b253-7b8363445e40. Accessed 16 Dec. 2024.

Sperry, Roger Wolcott, and Colwyn B. Trevarthern. Brain Circuits and Functions of the Mind. Cambridge University Press, 1990, xx-xxi.

Uggetti, Carla, et al. "Bilateral Transfer Phenomenon: A Functional Magnetic Resonance Imaging Pilot Study of Healthy Subjects." The Neuroradiology Journal, vol. 29, no. 4, 2016, p. 250, doi.org/10.1177/1971400916631992. Accessed 16 Dec. 2024.

Yao, Wan X., et al. "Bilateral Transfer of Motor Performance As a Function of Motor Imagery Training: A Systematic Review and Meta-analysis." Frontiers in Psychology, vol. 14, 2023, p. 1187175, doi.org/10.3389/fpsyg.2023.1187175. Accessed 16 Dec. 2024.