| Reference | Downloads | Github

Delay in movie stimulus display

URL of experiment: Alice Drew / cinema_short · GitLab

Psychopy version: v2020.2.10 (also checked with latest version 2021.2.3 and problem still occurs)
Mac OS Catalina 10.15.4

Description of the problem: Hi, I’m running an experiment where participants watch movies and have to click a mouse at certain times in the movie (which I later compare to a matrix of timings with the moments I’m interested in). After finding my pilot data somewhat strange (I.e. not aligning with expectations), I checked for the start and stop times of the movie and noticed that the movies tend to last about half a second longer than their actual length when played online (my pilots were using Macintosh or Windows and either Google Chrome or Firefox, the recommended browsers for timing)… My guess is that there might be some accumulated delay online. This makes it virtually impossible for me to make sense of the responses as I won’t know with certainty what participants were clicking at. Has anyone experienced this and does anyone know how to fix it? If there is a way to control for it, that would be great. If, as I fear, there will be individual variability based on computer, internet quality, open tabs etc, then it might be harder.

Looking forward to any insight! Thank you in advance!

Hi Alice,

How did you store the start and stop times of the movies out of interest? Was it via a code comp? (asking because I don’t think component start and stop times work yet online).

It is possible that if your participant had other background processes happening that frames were dropped during movie presentation (perhaps not if you were piloting yourself?).


Hi Becca,

Thanks so much for your response. Yes, I stored the start and stop times using code, as I saw the Save Onset/Offset function was only functional offline for now. It seems to save correctly as the output displays like this: Screen Shot 2021-11-10 at 1.55.56 PM

I worry that you’re right - ppts might have open tabs/different internet quality but since the response I’m recording is ‘free’ (i.e. following instructions about what happens in the movie but not measured relatively to a stimulus for instance), I worry that it will be very hard to control for this, as regardless of what participants say, I will never know exactly what they are seeing on the screen (i.e. what exact point of the movie). Here is the code I used: I also tried it in ‘each frame’ to see if it gave more insight.

Have you ever come across something similar? Thank you very much again for your help.

Hi @alicealbertinidrew

PsychoPy cannot translate thisExp.addData() properly. Change it (in the right panel only) into psychoJS.experiment.addData(). Though I do not if it will work for the reason @Becca mentioned.

Hi Yiannis, thanks for this suggestion, I tried it but it still yields the same result (as in the delays I show above)

Hi There,

Actually the newest release can translate this! so I would suggest updating to the newest release (infact I would highly recommend that in general - I just saw that you are on a 2020 release and things have improves alot since then).


1 Like