Masked priming

Flash a prime briefly, mask it, then time a choice response to a probe.

When to use it

Use this when the question is what a briefly presented prime does to the response that follows, without giving participants time to consciously inspect it. Simply flashing the prime and showing the probe is not enough: the visual trace of a 50 ms image outlives its offset, so an unmasked prime remains readable well past its nominal duration. Filling the gap with a pattern mask cuts that trace off at a known moment. If prime visibility is not a concern, drop the mask and just run two screens in sequence.

Trial file

type	stimFormat	stim1	stim2	mask	presTime	ISI	keyboard	key
test	.png	prime_doctor	probe_nurse	noise_mask	50	150	f j	f
test	.png	prime_table	probe_nurse	noise_mask	50	150	f j	f
test	.png	prime_doctor	probe_blint	noise_mask	50	150	f j	j
test	.png	prime_table	probe_blint	noise_mask	50	150	f j	j

How it works

The trial has two screens because ISI says so: stim1 (the prime) opens screen 1, and the single ISI entry pushes stim2 (the probe) onto screen 2. The presTime value 50 times the prime only. With two screens and exactly one duration listed, the probe screen deliberately has no duration, so it stays up until the participant responds.

The mask image is shown during each inter-screen gap, so noise_mask.png fills the whole 150 ms ISI between prime offset and probe onset. Two constraints from the mask page shape the design: the mask only loads on image trials (word trials leave the mask slot empty or stale), and it never shows without a numeric presTime on the screen before the gap. That is why the stimuli are images, with the extension declared once in stimFormat and bare basenames in the stim cells.

The participant makes a lexical decision on the probe: keyboard accepts F or J, and key scores F (word) or J (nonword) into the correct results column. Keep key lowercase; a response that matches only after ignoring case is recorded as unscored rather than incorrect.

Variations

• Vary the prime duration per row, for example 33|50 as the first presTime entry; the value is drawn once per row when the experiment loads.
• Stretch or shrink the prime-to-probe interval by changing ISI; the mask fills whatever gap you set.
• Add a response deadline with responseWindow, for example 2000; a timed-out trial records the response timeout.
• Show a fixation cross before the prime by adding an ITI duration plus fixation set to the exact token ITI.