Two streams.
The same simple rule.

Each cue shows a square and plays a spoken letter. Compare each with the cue exactly N steps earlier.

Start with N = 1.

Prefer to try it? Take the guided lesson, or step through the visual N=2 example.

At N = 1, compare with the previous cue. At N = 2, compare with the cue two steps ago, ignoring the one in between. Positions and letters are separate: either, both, or neither can match.

Press the buttons, not the square.

Tap Position and Sound, or use A and L on a keyboard. Press any time after a cue appears and before the next one starts. The square disappears quickly; you still have time to respond. Each button records one press per cue.

The first N cues are for remembering.

They cannot match anything yet, so the response buttons stay off. After those first cues, a round has 20 scored cues. Each cue lasts three seconds.

Check the sound first.

Turn up your volume and use Sound check. You should hear “C.” Keep this page in front while playing. Switching tabs, leaving the window, or losing audio stops the round. Use Stop round or Escape whenever you need a break.

Read your result.

Position and Sound each get a score. A correct press on a match and a correct wait on a non-match both count. Missed matches and extra presses count as errors. The overall score is the lower of your two scores, not an IQ or health measure.

Pick a level that lets you follow the rule. You can replay at the same level or change N yourself. Browser results are not saved or shared.