Reaction faster than action, study finds
British researchers inspired by the gunfights in old Westerns have found that people move faster when reacting to outside changes than when they decide to move on their own.
The scientists at the University of Birmingham say their work could lead to a better understanding of how the brain handles intentional and reactive movements differently, which is important for understanding conditions such as Parkinson's disease.
Each player in the game had three buttons in front of him, and each was challenged to push the three buttons faster than his opponent.
There was no starting signal, however, so a player either initiated the button-pressing movement or reacted to his opponent's movements.
The researchers found that players who reacted to an opponent completed the movement on average 21 milliseconds faster than those who drew first.
"As a general strategy for survival, having this system in our brains that gives us quick-and-dirty responses to the environment seems pretty useful," Welchman said in a statement.
"Twenty-one milliseconds may seem like a tiny difference, and it probably wouldn't save you in a Wild West duel because your brain takes around 200 milliseconds to respond to what your opponent is doing. But it could mean the difference between life and death when you are trying to avoid an oncoming bus."
The difference in the two types of movements can be seen in people with Parkinson's disease who, in some cases, can struggle to pick up a ball from a table but will easily catch a ball thrown at them, the researchers said.
The reason for the difference in speed between the two types of movement isn't clear, Welchman said, but it probably has to do with the different ways the brain handles actions we initiate and reactions to changes in our environment.
"Our experiment hasn't tested that directly, but one speculative idea is that there are different routes to the production of these different types of movements," Welchman said.
When we see a change in the environment and make a reaction to it, the signal comes in through the eye, gets sent to the back of the brain and from there to the areas that control movements.
When we initiate the movement ourselves, the signal originates in the decision areas at the front of the brain and goes from there to the movement centre.
"The key idea is that effectively the brakes get taken off faster when we're making a reactive movement, so we can get moving faster, than when we make an intentional movement," he said.