When prompted, press the spacebar. Stare at the cross in the center. 5 to 7 seconds later, a symbol will flash on either the right or left side. You will have to click the symbol that you saw from a selection of 4 symbols. In total, you will repeat this ten times, progress being show in the top-left hand corner. You can find you score in by clicking the button fittingly named "Scores".
I created this for a school project, but anyone can use it. Enjoy!
