The quick and the dead: evidence that movement is swiftest in response to events
3 February 2010
The research, funded by the Wellcome Trust and the Biotechnology and Biological Sciences Research Council (BBSRC), is published today in 'Proceedings of the Royal Society B'.
Nobel Laureate Niels Bohr, inspired by movies of the Wild West where the man who draws his gun first is the one to get shot at, suggested that the intentional act of drawing and shooting is slower than the act of firing in response to another's initial action. In other words, the 'quick draw' is the one responding to their opponent's action rather than the one initiating the dual.
Dr Andrew Welchman, who led the research, says: "In our everyday lives, some of the movements we make come about because we decide to make them, while others are forced on us by reacting to events. Bohr's suggestion reflects this everyday intuition. We wanted to know if there was evidence for these reactive movements being swifter than the equivalent proactive ones."
The researchers set up a competition between two people who were challenged to press a row of buttons faster than their opponent. There was no 'go' signal so all they had to go by was either their own intention to move or a reaction to their opponent.
The team found that the participants who reacted to their opponent executed the movement on average 21 milliseconds faster than those who initiated the movement. However, they did not respond as accurately in the test.
"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," says Dr Welchman. "21 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 team are now interested to know if there are two different brain processes happening for the two types of action. For example, people with Parkinson's disease find intentional movements far more difficult than reactive ones - they find it much harder to pick up a ball than to catch the same ball if it were thrown at them. This might be evidence that particular areas of the brain affected by Parkinson's contribute more to intentional actions than reactive ones. If this turns out to be the case, then it might also be possible to develop strategies to ease movement in such patients.
Image: Four cowboys. Credit: anyjazz65 on Flickr
Reference
Welchman AE, et al. The quick and the dead: when reaction beats intention. Proc. R. Soc. B 2010 [Epub ahead of print]
