A square flashes in one of eight places, and a letter is spoken. Press A if the square is where it was n trials ago; L if the letter is the same. Do nothing when neither matches. After each block, n rises if both streams had fewer than three mistakes, and falls if either had more than five. Twenty blocks is a session, about twenty minutes. Letters are spoken — turn the sound on.
The board is a three-by-three grid with the middle left empty, so there are eight places a square can appear. Every three seconds one trial happens: a single square fills in for half a second, and at the same moment a voice says one letter, drawn from B, F, H, J, M, Q, R and W. Then the square clears and you wait for the next trial. The two streams are independent — the square and the letter know nothing about each other — which is what makes it dual n-back. If your browser cannot speak, the letter is printed in the middle of the grid instead.
You are not asked to remember the whole sequence. You are asked one question per trial, about each stream separately: is this the same as n trials ago? At 2-back you compare the current trial against the one from two trials earlier — not the one just before it, and not any earlier one. There are four possible answers each trial, and three of them require you to press something:
Press any time while the trial is on screen; you have the full three seconds, not just the half second the square is lit. Pressing the same key twice in one trial is harmless. On a phone or tablet, tap the two on-screen buttons instead of typing. The first n trials of every block have nothing behind them to compare against, so they can never be matches — watch and listen, but do not press.
Positions are named by where they sit in the grid. Read down the table one row at a time and cover the last column until you have decided for yourself.
| Trial | Square | Letter | Compare against | Correct response |
|---|---|---|---|---|
| 1 | upper-left | Q | — nothing yet | nothing |
| 2 | right | B | — nothing yet | nothing |
| 3 | upper-left | M | trial 1: upper-left, Q | A — same place, different letter |
| 4 | bottom | B | trial 2: right, B | L — same letter, different place |
| 5 | bottom | H | trial 3: upper-left, M | nothing |
| 6 | bottom | B | trial 4: bottom, B | A and L — both |
| 7 | left | W | trial 5: bottom, H | nothing |
| 8 | bottom | W | trial 6: bottom, B | A — same place, different letter |
Two rows there are traps worth naming. On trial 5 the square is at the bottom and so was the square on trial 4, one trial earlier — but one back is not two back, so you press nothing. On trial 8 you have just heard W on trial 7, which feels like a match and is not; the letter you must compare against is trial 6's B. Almost every mistake beginners make is this one: answering against the trial you just saw rather than the one n trials back. The sequences here are built with such near-misses on purpose.
Each stream is scored on its own, and each trial can cost you at most one mistake per stream. Missing a real match costs one; pressing when there was no match costs one. Staying silent through a trial with no match is correct and costs nothing. A block at n-back runs 20 + n trials and contains six position matches and six letter matches, two of which are the same trial — so roughly a quarter of trials want a press and the rest want silence. Withholding is a skill in itself.
You start at 2-back. At the end of each block the line under the grid reports your errors in each stream and what happens next:
Drifting down is not failure; the whole point is that the task tracks you and keeps sitting just past what you can comfortably hold. A session is twenty blocks, about twenty minutes, and your score is the mean n across those blocks. Your last mean, your best mean and your highest n are kept in this browser.
A position · L letter
Mean n: 0