There is a cursor where the light phaser points. Only the bar around the target is illuminated. Find the color red and shoot it within 3 seconds. Miss once or let time expire, and you go back to the title screen. Complete all 20 rounds and your score is compared against a table that determines your average reaction time. You can use the d-pad instead of the light phaser, but it's much harder to get a good score.
By DragonFeet