Video then buttons

Play a video clip and only reveal the response buttons once playback has finished.

When to use it

The participant must watch a clip in full before judging it. With buttons active from trial start, impatient participants answer mid-clip and their RTs mix viewing time with decision time. Gating the response window until playback ends keeps the clip unskippable and makes RT a clean decision time measured from the final frame. If the judgement is about which of several stimuli to pick rather than a verdict on one clip, clickable stimuli fit better than buttons.

Trial file

type	content	stimFormat	stim1	responseWindow	button1	button2	key
instructions	Watch each clip, then judge whether the smile is genuine or posed.				Start
test		.mp4	smile1	afterStim	Genuine	Posed	1
test		.mp4	smile2	afterStim	Genuine	Posed	2
test		.mp4	smile3	afterStim	Genuine	Posed	1
test		.mp4	smile4	afterStim	Genuine	Posed	2

How it works

stimFormat set to .mp4 makes each row a video trial: stim1 holds the basename and the extension is appended automatically. There is no presTime; the clip’s own length decides how long it plays.

responseWindow: afterStim is the gate. On video trials that start position opens the window only after playback ends, and because buttons appear once responses are enabled, Genuine and Posed are simply not on screen while the clip runs. When it finishes the buttons show, the window opens, and RT counts from that moment, so the recorded time is decision time rather than clip length plus decision time. The position is case-sensitive: afterstim is not recognised, and an unrecognised position means the window never opens and the trial hangs collecting nothing.

The buttons carry the response. A click records the button’s number, 1 or 2, not its label (the visible label is saved separately in the results), and key scores against that number: 1 marks Genuine correct, 2 marks Posed correct, filling the correct results column.

The button1 cell on the instructions row does double duty: on instruction trials it relabels the advance button, so the run opens with a Start button rather than the default NEXT.

Expect the automatic “enable media autoplay” screen at the start of the run; any project containing media inserts it, and it is what lets the clips start unattended.

Variations

• Add a post-clip deadline with afterStim_3000 in responseWindow; no click within 3 s records the response 999, marked as a timeout, and auto-advances.
• Show native playback controls with controls in stimOptions, or keep the final frame on screen behind the buttons with keep.
• Accept keys as well by filling keyboard (for example g p); buttons and keyboard coexist on the same trial, though key and button responses record different values, so score accordingly.
• Let the clip repeat until the response by adding loop to stimOptions for self-paced viewing (drop the afterStim gate in that case, since looping playback does not end).