Gif display times varying?

thv — Thu, 19 May 2016 11:46:04 GMT

Hello,
I am programming an experiment that presents several .gif images, however the times of the gifs seem to be varying unexpectedly (even when they should be the same length).
When I changed it to present the same gif for 4 trials in a row, the first trial is often about twice as long as the rest of them, but occasionally other trials are much longer than the others. (It does not have this issue for static images.)
Has anyone encountered this issue, or know how to solve it? Any help would be much appreciated.

Here's a bit more information:
I tried recording the time each image was displayed for (as suggested in this post http://www.millisecond.com/forums/Topic16654.aspx?Keywords=time-spent-on-page). According to that post, because its being recorded starting from ontrialbegin (rather than the stimulus onset) it will record the times with some additional variability (up to 100ms), which is not actual variability in the presentation times. I see this when I time some static images, but the variability in my gifs is definitely more that that (several hundred ms) and is noticeable to the naked eye.

Here's how I'm recording the times, and below is some of the times I recorded
<trial fastfractaltrial>
/ ontrialbegin = [values.t_start=script.elapsedtime;]
/ stimulusframes = [1 = fastfractals]
/ response = timeout(1)
/ recorddata = false
/ ontrialend = [values.t_end=script.elapsedtime;]
</trial>

<values>
/ t_start = 0
/ t_end = 0
</values>

<expressions>
/ imagedisplaytime = (values.t_end-values.t_start)
</expressions>

Here is an example where I took 2 different gifs (one shorter and one longer), and presented them in blocks of 4.
The largest delay seem to be the first time each gif is used, though e.g. the 3rd trial here is also much longer.

trialtype	imagedisplaytime
short	734
short	295
short	796
short	312
long	793
long	547
long	463
long	461
short	276
short	308
short	295
short	295
long	477
long	445
long	467
long	494

RE: Gif display times varying?

Dave — Thu, 19 May 2016 11:46:04 GMT

I seem to be unable to reproduce this. Here's the code I'm using, which mimics yours:

<expt>
/ blocks = [1-4 = myblock]
</expt>

<block myblock>
/ trials = [1-4 = mytrial]
</block>

<trial mytrial>
/ ontrialbegin = [values.t_start=script.elapsedtime;]
/ stimulusframes = [1 = mygif]
/ response = timeout(1)
/ ontrialend = [values.t_end=script.elapsedtime;]
</trial>

<video mygif>
/ items = ("short.gif", "long.gif")
/ playthrough = true
/ select = sequence
/ selectionrate = block
/ resetinterval = 0
</video>

<values>
/ t_start = 0
/ t_end = 0
</values>

<expressions>
/ imagedisplaytime = (values.t_end-values.t_start)
</expressions>

<data>
/ columns = [blocknum trialnum stimulusitem values.t_start values.t_end expressions.imagedisplaytime]
/ separatefiles = true
</data>

The "short" GIF has 10 frames and an expected duration of approx. 700ms given the GIFs settings and the test system's refresh rate. The "long" GIF has 20 frames and an expected duration of a little more than twice that of the "short" GIF. Both files are attached. The tests were conducted using the latest Inquisit 4 release (if you are using some older version, please update). The data I'm getting corresponds well with what would be anticipated under those circumstances:

blocknum    trialnum    stimulusitem1    values.t_start    values.t_end    expressions.imagedisplaytime
1                    1                 short.gif               64                        754                     690
1      2                 short.gif               904                      1625                  721
1                    3                 short.gif               1642                    2345      703
1                    4                 short.gif                2362                   3066                  704
2                    1                 long.gif                 3150                   4591                  1441
2                    2                 long.gif                 4608   6049      1441
2                    3   long.gif   6065                   7507                  1442
2                    4                 long.gif    7523    8964      1441
3                    1    short.gif    9050                   9752   702
3                    2   short.gif               9769                   10473   704
3                    3                 short.gif               10489               11193                 704
3                    4                 short.gif               11210                 11914               704
4                    1                 long.gif                11999                 13439                1440
4                    2                 long.gif                13455                 14896      1441
4                    3                 long.gif                14913                 16354      1441
4                    4                 long.gif                16371                 17812                1441

I suppose there must be some additional factors at play here, although I am not sure what they may be. Perhaps it's something about the specific GIFs you are using. Perhaps there is some deeper issue with the system you have observed this on (this could be ruled out by replicating it on other systems). If you can think of anything, please add it to this thread. It would also be interesting to know the results of running the attached test script on your system(s).

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Gif display times varying?

RE: Gif display times varying?