ITI

Experiments Surveys & forms Surveys apply the delay normally; form pages in old-style form projects default to 500 ms and read only a plain integer from the cell.

ITI (inter-trial interval) is the blank delay, in milliseconds, inserted at the START of a trial before its stimuli appear. During the delay the trial’s ITI fixation and ITI trial text (if configured) are visible. Use it to create rest gaps between trials or to guarantee a fixation period before each stimulus.

Syntax

Put the delay in milliseconds in the cell: an ITI of 1000 gives a one second blank before the trial’s stimuli appear.

Two other forms are available, both worked out afresh every time the trial is presented:

• min_max, a random whole number of milliseconds between the two values, inclusive
• a|b|c, one of the listed values picked at random

One value per cell. Semicolon lists and the V*N repeat syntax are NOT supported for ITI; they exist only for ISI and presTime.

Options

Value	Behavior
empty (or absent)	No delay: the stimuli appear immediately. ITI_ms stays blank for that trial.
0	Same immediate behavior. The column still counts as present for results.
positive integer	Stimuli appear after that many ms. Values at or below half a screen refresh fire immediately.
min_max	Random ms between min and max, fresh draw per presentation.
a|b|c	Random pick per presentation.
non-numeric	No delay, as for an empty cell.
Nf	Accepted as a frames value but the leading number is what counts, so it currently behaves as N ms (see the tips on the presTime page).

Defaults & missing values

Leave the cell blank, or leave the column out of the file, and there is no delay: the trial’s stimuli appear straight away, and ITI_ms stays blank for that trial.

There is no project-wide fallback for stimulus trials. Old-style form trials are the exception: they wait 500 ms when ITI is blank.

Works with

• Trial types: the delay applies to image and word trials, audio and video trials, surveys, and HTML app trials. Instruction screens skip it entirely.
• type=instructions with presTime: the screen advances by itself after presTime plus ITI (plain whole numbers only), even though no visible delay happens first.
• fixation: the value ITI (or the legacy 1) shows the fixation cross during the delay; it is hidden once the stimuli appear, unless allTrial, allStim or withStim keeps it on screen.
• trialTextOptions: the option ITI displays the first trialText segment during the delay, and hides it when the delay ends.
• auxiliary audio column on image and word trials: with an ITI above 0 the audio is fully buffered before the stimuli appear; with a blank or 0 ITI it starts immediately.
• old form trials: ITI replaces their 500 ms default, but only the leading number is used, so the random forms degrade there (500_1500 becomes 500).
• Results: the measured delay is saved as ITI_ms for each saved test trial, with ITI_f and ITI_fDuration alongside it. learn and practice trials are not recorded. The three columns appear as soon as any test trial has been saved, even if no trial ever used ITI.

Examples

1. Fixed 1 second gap with a fixation cross before each stimulus:

type	stimFormat	stim1	ITI	fixation	keyboard	key
test	.jpg	face01	1000	ITI	f j	f

2. Jittered gap, re-drawn every time the trial row is presented:

type	stimFormat	stim1	ITI	keyboard	key
test	.png	word	500_1500	a l	a

3. Discrete jitter from three alternatives:

type	stimFormat	stim1	ITI
learn	.jpg	study_item	800|1200|1600

Tips & gotchas

Note

The ITI belongs to the trial it delays, not to the trial before it. The last trial of a session therefore still pays its own ITI, and the first trial’s ITI runs before anything has been answered.

• Instruction screens never wait for ITI, but silently fold it into the presTime auto-advance total.
• Random ITI values do not work on instruction trials: a value such as 500_1500 counts as 0 there.
• The three ITI results columns can line up differently. ITI_f and ITI_fDuration get one entry per stimulus trial that actually waited (every type except learn and practice), while ITI_ms gets one entry per saved test trial, so a survey or form trial with an ITI adds rows to ITI_f with no matching ITI_ms row. A test trial whose delay was not measured can also report the previous trial’s measured value.

Common combinations

ITI appears in these worked recipes:

• Fixation, then stimulus: Show a fixation cross, then a single timed stimulus with a keyboard response.
• Fixed trial duration: Make every trial last exactly the same time whether the response comes early, late, or not at all.
• Jittered RT task: Measure choice reaction times with an unpredictable interval before each stimulus.
• Dot-probe task: Show a pair of images side by side, replace one with a probe, and measure how fast the probe’s location is reported, in one row per trial.