Three-screen sequence

Present a context scene, a studied pair, and a memory probe as three timed screens within a single trial.

When to use it

Encoding-and-probe designs often need more than a prime and a target: a context screen, a study display, then a test display, each with its own duration and clean blank gaps in between. Splitting the sequence across separate trial rows breaks the design, because the response and its timing belong to the sequence as a whole, not to the last row. This recipe builds the whole sequence inside one trial, including a screen that holds two stimuli at once.

Trial file

type	stimFormat	title	content	stim1	stim2	stim3	stim4	presTime	ISI	keyboard	key	button1
instructions		Remember the objects	You will see a room and then two objects from it. After a pause a single object appears. Press F if it was one of the two and J if it is new.									NEXT
test	.png			scene_kitchen	obj_kettle	obj_mug	obj_kettle	2000;1000	500;;300	f j	f
test	.png			scene_office	obj_stapler	obj_lamp	obj_clock	2000;1000	500;;300	f j	j
test	.png			scene_garden	obj_spade	obj_flowerpot	obj_flowerpot	2000;1000	500;;300	f j	f
test	.png			scene_garage	obj_hammer	obj_torch	obj_saw	2000;1000	500;;300	f j	j
test	.png			scene_bathroom	obj_towel	obj_brush	obj_towel	2000;1000	500;;300	f j	f
test	.png			scene_bedroom	obj_lamp2	obj_book	obj_shoe	2000;1000	500;;300	f j	j

How it works

The screen layout is written entirely in ISI. Its entries describe the break after each stimulus in turn, and 500;;300 reads: a 500 ms gap after stim1, no break after stim2 (the empty middle entry), and a 300 ms gap after stim3. The empty entry is the grouping syntax: with no break between them, stim2 and stim3 share a screen. The result is three screens from four stimuli: the scene alone, the two objects together, and the probe alone. Do not add a trailing semicolon; a trailing empty entry still counts as a break and silently rearranges which stimuli reach the screen.

presTime then times the screens one entry each: 2000;1000 gives the scene 2000 ms and the study pair 1000 ms, and with exactly one entry missing the final screen deliberately has no duration, so the probe stays up until the F or J response. That missing-last-entry trick only works because every earlier screen has a positive duration; each gap is timed from the moment the previous screen comes down, so a 0 or empty duration mid-sequence stops the trial there and the later screens never appear.

The gaps themselves are genuinely blank. A gap only shows content when the trial has a mask, an ISI fixation, or ISI trialText configured; with none of them, the participant sees an empty screen for 500 and 300 ms. key scores the old and new probes against the two keyboard keys, and the measured gaps are written to the ISI_ms results column, so the realised timing is checkable per trial.

Variations

• Regroup without the empty entry: with fewer ISI entries than stimuli, the leftover stimuli land together on the last screen, so 500;300 gives scene, object, then a two-object final screen; drop keyboard, put the remembered object in slot 3, and score the click with key set to stim3.
• Fill the gaps deliberately: a mask image shows during every gap of a sequential image trial, or set fixation to the token ISI for a cross instead.
• Jitter the pauses with min_max entries such as 400_800;;300 in ISI; the draw happens once per row when the experiment loads.
• Equalise screen times with the repeat syntax: a presTime of 1000*2 is the same as 1000;1000.