You will hear 15 notes, every time 220Hz. Some of them have a flipped phase. Below you see two lines of 14 buttons. After every note you have to decide if the note sounded identical to the note before, or if it changed. (Example: If you think note One and Two sounded alike, you press the upper button in the first row. If you think note Two and Three sounded different, you press the lower button in the second row and so on.)

You can replay the sample as often as you want, but only submit the form one time.