mask

Experiments

mask names an image shown as a backward mask after the stimuli are hidden. It renders in its own dedicated slot on the screen. Use it in perception/priming designs where the stimulus offset must be masked instead of leaving a blank screen.

Syntax

Put the mask image’s filename in the cell, normally WITHOUT extension (e.g. noise_mask); the stimFormat extension is appended exactly as for other image stimuli, unless the cell already ends with it. Leave the cell empty for no mask. The mask is always an image; text patterns are not supported.

Options

Value	Behavior
empty cell	No mask; on timed simultaneous trials the stimuli are simply hidden after presTime
<basename>	Preloaded and displayed as an image, centered on the canvas
<basename>.<ext>	Extension kept if it matches the stimFormat

There are no sub-options.

Defaults & missing values

When the column is absent or the cell is left blank, no mask is shown. The mask image is preloaded only on image trials; on other trial types it is never loaded (see Tips & gotchas). A mask name containing a %...% variable is not preloaded.

Works with

• presTime (simultaneous image trials): with presTime set, the stimuli are replaced by the mask when their time is up, instead of simply disappearing. The mask then stays visible until the trial ends. Without presTime, the mask never shows.
• ISI (sequential/multi-screen trials): the mask is shown during every inter-screen gap after each screen’s presTime and hidden again when the next screen starts. It is NOT shown after the LAST screen, which is the opposite of the simultaneous case where the mask appears after the single screen ends.
• Size and position: the mask displays at its natural image size (scaled with the overall display); stimSize and stimPos do NOT apply. It is always centered on the canvas.
• Trial text: when a mask exists, its extent is taken into account when placing the trial text vertically.
• type learn: on masked trials, the trial auto-advances when the mask appears.
• responseWindow afterStim behaves differently when a mask is present: the response-window start and the trial-text show/hide tied to stimulus offset do not apply in the masked case.

Examples

type	stimFormat	target	presTime	mask	keyboard	key
test	.jpg	prime_word	50	noise_mask	f j	f

prime_word.jpg for 50 ms, immediately followed by noise_mask.jpg (centered), which stays up while the participant answers with F/J.

type	stimFormat	stim1	stim2	stim3	ISI	presTime	mask
test	.png	item1	item2	item3	500;500	200;200;200	checker

Each item is shown 200 ms; during each 500 ms gap checker.png is displayed as the mask.

Tips & gotchas

Caution

Use mask on image trials only. On sequential WORD trials the mask image is never loaded, so the mask slot shows an empty or stale image from a previous image trial. Simultaneous word trials ignore mask entirely.

• A mask requires a numeric presTime; a mask with no presTime never shows.
• Masks do not apply on trials whose test column is CFPT.
• The mask can render at a slightly different position than the stimuli it replaces.
• In the simultaneous case nothing hides the mask before the next trial: it persists through the response period.

Common combinations

mask appears in these worked recipes:

• Masked priming: Flash a prime briefly, mask it, then time a choice response to a probe.