Between-subject conditions

Give each participant one of two stimulus sets, while shared screens run for everyone.

When to use it

Use this when a manipulation must differ between participants, for instance when seeing one condition would contaminate responses to the other. The tempting workarounds both cost you: duplicating the project per condition doubles maintenance and splits the results into separate files, while showing everyone everything quietly turns the design within-subject. Tagging rows with subjectGroup keeps one project, one results file, and an automatic condition label per participant. If every participant can safely see all conditions, prefer a within-subject design with random and a condition column instead.

Trial file

type	content	stimFormat	stim1	subjectGroup	random	keyboard	button1
instructions	Rate each image from 1 (unpleasant) to 7 (pleasant).						NEXT
test		.png	forest	1	1	1 2 3 4 5 6 7
test		.png	lake	1	1	1 2 3 4 5 6 7
test		.png	waterfall	1	1	1 2 3 4 5 6 7
test		.png	street	2	1	1 2 3 4 5 6 7
test		.png	carpark	2	1	1 2 3 4 5 6 7
test		.png	overpass	2	1	1 2 3 4 5 6 7
test		.png	grey_square			1 2 3 4 5 6 7

How it works

subjectGroup splits the sample: rows tagged 1 belong to the nature condition, rows tagged 2 to the urban condition, and each participant is assigned one subgroup per session (randomly by default, or evenly across participants when the project’s even-allocation setting is on). They then see only their subgroup’s rows plus every untagged row, so the instructions screen and the shared baseline image run for everyone. The assigned subgroup is saved into the results as a subjectGroup info column (1 or 2), which is your condition label at analysis time.

The rating itself needs no scoring, so there is no key column: keyboard lists the digits 1 to 7 and the pressed digit is recorded as the response. The tagged rows all carry 1 in random, so the six of them shuffle as one run; group filtering happens after the shuffle, leaving each participant their three rows in random order. The baseline row’s empty random cell keeps it last for everyone.

Use bare integers consistently: mixing them with named label:N values in one file makes the bare integers’ group depend on the shuffled order, and a bare word like A silently creates no group at all.

Variations

• Cross two factors: use named groups in subjectGroup (scene:1/scene:2 on these rows, order:1/order:2 on others); one subgroup is picked independently per label, and the results record something like scene:1 order:2. Use the named form everywhere or the bare form everywhere, never both.
• Balance the split: turn on the project’s even-allocation setting so subjectGroup assigns each new participant the least-filled subgroup instead of a random one.
• Give one condition its own rest point: a break row tagged 2 in subjectGroup is filtered like any trial row, so only that group gets the break.