A pair of stimuli is shown together — a symbol and a number — and after a short delay you are asked to recall which number belonged with which symbol. Every option on offer is something you genuinely saw during study, so recognising it is worthless; only the correct binding scores.
Why airlines test it
Associative or paired-associate memory is not the same skill as remembering a list. It measures whether a candidate can bind two unrelated pieces of information into a single durable link, then retrieve that link intact after a delay designed to let it interfere with everything else studied around it. Selection boards care about this because flying is full of arbitrary pairings that must not cross-contaminate: this frequency with that station, this restriction with that waypoint, this clearance with that aircraft. A candidate who confuses which number went with which symbol under mild interference is showing exactly the failure mode that produces a misapplied clearance on a busy frequency.
In the cockpit
On a congested frequency you are holding several callsign–instruction pairs at once — who was told to hold, who was cleared to descend, who still owes you a readback — and the aircraft themselves are not shown to you in a tidy list; you have to keep the bindings straight purely from memory while other traffic talks over the top of them. The danger is not forgetting an instruction outright, it is misattributing it: applying the descent clearance meant for one aircraft to another with a similar callsign, which is precisely a paired-associate error.
For example: ATC issues 'Speedbird 23, descend to FL80, QNH 1013' followed thirty seconds later by 'Speedbird 32, descend to FL100, QNH 1015' on the same frequency. If you bind the FL80/1013 pair to the wrong callsign under the interference of the second transmission, you read back — and fly — the wrong level and the wrong pressure setting for your own aircraft, a paired-associate slip with real separation consequences.
How to practise
Play Associative Memory and resist the urge to just recognise numbers — during the study phase, actively narrate each symbol–number pair to yourself rather than passively looking at them, since passive familiarity is exactly what the retention delay is designed to strip away. Track your accuracy rather than your raw score: a wrong recall costs a point precisely because guessing on a pair you never actually bound is worse than admitting you do not know, so treat every confident wrong answer as a sign your binding, not just your memory, needs work.