AX-CPT

Present a cue and then a probe as two screens of one trial, with the correct response depending on the cue-probe pair.

When to use it

Use this for cue-probe paradigms like the AX continuous performance task, where the response rule spans two events: press target only when the probe X follows the cue A, and non-target for every other combination (AY, BX, BY). The pair must behave as one unit, one reaction time, one accuracy, one row in the results, so both events belong inside a single trial as two consecutive screens, not in separate rows. The design’s signature conditions (BX probing cue-driven errors, AY probing probe-driven ones) are just rows with the right pairs and keys.

Trial file

type	content	stimFormat	stim1	stim2	presTime	ISI	pair	trialOrder	keyboard	key	button1
instructions	You will see two letters, one after the other. Press F only when X follows A. Press J for every other pair.										NEXT
test		word	A	X	500	1000	AX	1: shuffle; maxRun 2 pair	f j	f
test		word	A	X	500	1000	AX	1	f j	f
test		word	A	X	500	1000	AX	1	f j	f
test		word	A	Y	500	1000	AY	1	f j	j
test		word	B	X	500	1000	BX	1	f j	j
test		word	B	Y	500	1000	BY	1	f j	j
test		word	A	X	500	1000	AX	1	f j	f
test		word	A	Y	500	1000	AY	1	f j	j
test		word	B	X	500	1000	BX	1	f j	j
test		word	A	X	500	1000	AX	1	f j	f

How it works

stim1 is the cue and stim2 the probe, presented sequentially: presTime = 500 times the cue’s screen, and with one entry missing the probe screen deliberately has no duration, so the probe stays up until the response. ISI = 1000 is the cue-probe interval, a blank second in which the cue must be held in mind, which is the working-memory load the task exists to measure.

key encodes the pair rule row by row: f on AX rows, j everywhere else. Reaction time is measured from the probe by default, since responses open when the last stimulus appears. The pair column is a custom annotation passing the condition label through to the results, and the ordering spec 1: shuffle; maxRun 2 pair (written on any one row of the group) randomises the trials while keeping more than two of the same pair type from stacking up in a row.

The AX rows outnumber the others on purpose: the task works because AX is frequent enough to build a strong expectation, which BX and AY trials then violate in their two different ways.

Variations

• Make the cue-probe interval jitter: ISI = 800_1200 draws each trial’s interval once from that range when the session loads.
• A response deadline: responseWindow = 1300 scores slow responses as timeouts, the standard AX-CPT constraint.
• Longer cue exposure or a masked cue: adjust the first presTime entry, or insert the mask as stim2 and move the probe to stim3, giving the mask its own presTime and ISI entries (stimuli present in slot order).
• Scale the AX proportion by adding or removing AX rows; keep maxRun consistent with what the counts allow, or reduce the spec to 1: shuffle for a plain shuffle.