After you click the button to begin, a rectangle will appear to the right of the button. Half of the time the rectangle is small and half of the time it is big. The simulation is started by clicking t...After you click the button to begin, a rectangle will appear to the right of the button. Half of the time the rectangle is small and half of the time it is big. The simulation is started by clicking the button in the lower left of the screen. Clicking this button begins a series of trials where a another button appears on the right and you will be asked to click this button as quickly as possible.