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The rule: position N-back
Prefrontal Gym uses a 3×3 grid of dots. At each step one position lights up briefly and then goes dark. Your job is to decide whether the position lit now is the same as the one lit n steps earlier. If it is, tap "Same". If not, tap "Different".
Each lesson begins with n warm-up positions that you only watch, because there is not enough history to compare yet. After that, every new position needs an answer. Each correct answer earns a fixed number of points, and correct answers in a row build a combo. Matches are the minority in each sequence, so most answers are "Different". Do not assume an answer before you see the position.
Levels 1 and 2: 1-back
1-back only asks you to compare with the previous position. It sounds easy, but it already contains the core N-back action: hold, compare, update. Each new position has to be compared with the last one and then becomes the "old" position for the next comparison.
Level 1 runs at a gentle pace to help you learn the controls. Level 2 is faster, so you have less time to react and update. The most common mistake here is simply missing a flash because you looked away or blinked. Keep your gaze resting on the centre of the grid instead of staring at one particular dot.
Levels 3, 4 and 5: 2-back
Going from 1-back to 2-back is where most people feel a sudden jump in difficulty. You now need to hold two positions in mind, and at every step you drop the oldest and add the newest. This sliding-window style of updating is one reason researchers have long used N-back tasks to study working memory.
Level 3 is standard 2-back. Level 4 speeds up the pace. Level 5 uses a longer sequence, which tests endurance: can you keep updating through the whole lesson without losing track? Many people suddenly "drop" the sequence in the middle, and once that happens the next few answers suffer too.
Level 6: 3-back
3-back requires you to hold the order of three positions. At this level, raw effort alone often is not enough, and many people naturally start to use strategies, such as numbering the nine dots and silently repeating a short string like "five, one, nine", or imagining the light moving along a route.
A clearly higher error rate on 3-back is normal. It is better used as an occasional challenge than as your default daily warm-up.
Practical memory strategies
- Number the grid. Picture the 3×3 grid like a phone keypad, 1 to 9. Each time a dot lights up, say its number silently. You end up holding a short string of digits.
- Only keep the window. At any moment you only need the latest n positions. Letting go of older ones on purpose is just as important as remembering.
- Update right after answering. As soon as you respond, add the new position to your string. Do not dwell on whether the last answer was right.
- Do not guess by habit. Matches are relatively rare. If you are unsure, decide from memory rather than tapping the same button by default.
Reading your N-back results
The main things to watch on the results screen are accuracy and combo. Within the same level, changes in accuracy are more informative than changes in points. A reasonable signal to level up is that you keep fairly high accuracy over several sessions and do not finish feeling exhausted.
If accuracy drops after levelling up, you are in a normal adjustment period. Alternate between the old and new levels for a few days. If you stay at low accuracy for several days in a row, stepping back one level is not a failure; it is simply a more effective plan.
Combining N-back with other tasks
N-back emphasises updating working memory. Backward digit span emphasises holding and rearranging a string of information. The Schulte grid emphasises visual search. Rotating among them keeps practice from becoming dull. On a tired day, warm up with a Schulte round first and then decide whether you want N-back at all.
It is worth saying plainly that researchers hold different views on whether N-back practice meaningfully improves everyday abilities, and the findings are not consistent. We suggest treating it as a focus exercise with clear rules and feedback, not as a shortcut to "raising your IQ".
Frequently asked questions
Why don't I answer the first few positions? In n-back you compare with n steps earlier. At the start of a sequence there is no history yet, so the first n positions only build your memory. Answers begin from position n+1.
Couldn't I score well by always pressing "Different"? Because matches are less common, always pressing "Different" might get a fair number right, but it removes the whole point of the exercise and misses every match. Judging each item honestly is the only way to get useful feedback.
Does it matter if I use a phone or a computer? The rules are the same; only the controls differ. Choose whichever device you tap most reliably on, and stick to it so your results are comparable.
A sample week with N-back
If you are new to N-back, a gentle first week might look like this. On days one and two, play level 1 once a day and focus only on not missing any flashes. On days three and four, try level 2 and notice how the faster pace changes things. On day five, take a first look at 2-back on level 3; expect it to feel hard and do not judge yourself by the result. At the weekend, choose whichever level felt right and play one relaxed round, or take a break entirely.
After that first week, many people settle into 2-back as their everyday level and visit 3-back occasionally. Whatever you choose, keep each session short. N-back is demanding, and one focused round is more useful than several tired ones. When the round ends, carry that focus straight into your next real task instead of starting another round.