The Simon effect [2] is a well known phenomenon in the field of experimental cognitive psychology; it is a basic measure of how quickly and accurately people can respond to visual information that contains "unconsciously distracting" information (which is very common in daily life too).
In the so called "Simon task", people need to respond quickly to images on the screen (in this case arrows), but responding is not always as easy as you think! For example, it is difficult to respond to an arrow that points to the left with a left-positioned button if that arrow appears on the right side of the screen (if you do not believe this, try it yourself).
I have created an on-line version that people from all over the world can participate in. People can see their own performance, as well as that of others. I hope that as many as possible people will participate in this study. Please spread the word about this study, which can participate in view this link: http://psytoolkit.gla.ac.uk/simon/ [3]