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Populating Loop cells from file

I have a program that populates loop-object fields from a csv file. When run "within browser" in OpenSesame, it works fine. When run through Jatos, the program hangs at the initial "loading experiment" page. Tested with an identical version in which the loop field values are hard coded within OpenSesame, and it works fine in Jatos, so there seems to be a limitation in using the file reference.

Any workaround to avoid this problem?

The goal of using the file reference is to avoid limitations on complex counterbalancing in OSWEB/JATOS. The plan was to use a different programming environment to do the counterbalancing and simply generate subject-specific lists of all the trial-level values (variable values and image files), with the appropriate loop file loaded for each subject based on subject number.

Thanks in advance,



  • Hi Andrew,

    If you could tell us what error messages, if any, you see in the console, we'll figure out where the problem is.

    But also, you can add a counterbalancing script in JATOS if you're willing to write a bit of JavaScript. We have some example studies in the JATOS docs that can serve as a good starting point.



  • Hi Andrew,

    What is the file path you are using for your file?



  • edited April 2020

    Thanks for the replies. This is a bit of an odd situation, because I want to get an existing experiment up and running quickly online without having to re-do all the counterbalancing script that we originally wrote in VisualBasic/E-prime. But, yes, the next step is to just re-do that code in JS if we can't get this kludgy workaround to work.

    And, apologies in advance for trying to do this with minimal working knowledge of OpenSesame or JS.

    So, I have simply been testing whether it is possible to use the "file" option in a loop object to specify the trial structure of the experiment on a subject-by-subject basis. To do that test, I first started with a visual search experiment that Sebastiaan sent me as JATOS-ready that I knew would work. I've uploaded it to the test server as "Visual Search Original". Of course, it runs perfectly.

    Then I have made one change to that OpenSesame program in the "block_loop" object, changing the method for populating the loop object fields to "file", saving the original contents of the loop object to a csv file, and then including the csv file in the file pool

    Runs perfectly fine within OpenSesame itself, even when run in a browser.

    I've uploaded this modified version to the test server as "Visual Search CSV".

    When running through JATOS, however, it hangs at the "loading experiment" screen:

    So, yes, probably a path problem, but its not clear to me how OpenSesame defines the path for files associated with loop objects.



  • Hi Andrew,

    I think your problem may be related to the fact that you use a 'file' as source. As described in the OSWeb manual, using files to populate loop cells is not supported (; see 'Supported functionality' section). If I am right, this is then more an OSWeb issue than a Jatos problem.



  • Thanks, that's it.

  • Glad that I found this post with the link to the osweb manual, as I've just run into the same problem, and has not noticed that 'except' in the 'supported' details. I was using files to avoid the bug where loop table column names are alphabetized but the rest of the rows are left alone, making garbage of the table. I will have to go back and paste my files into the loop template, having first made sure the columns are already in alphabetical order I suppose. Pity the compatability check doesn't spot this one as

  • Hi @Andrew,

    (ping @elisa @kri @GorinS @jmplym)

    As GorinS pointed out, the problem relates to the fact that not all functions and objects in OS work in OSWeb (the problem is not with JATOS). I ran into the same problem (in my experiments, the sequence of trials must usually follow fairly complex rules that may not even be practical to implement in Javascript because sometime the algorithm can't find a solution on the fly). Anyway, I started to explore an alternative solution to reading stimuli sequences from files that would work in OSWeb (it basically relies on creating memory arrays that are equivalent to the files, and reading from these). I described it here:

    It is a little cumbersome, for sure, but I share it (as is) in case it can help others. Hopefully, the developers of OSWeb will work our a way to authorize reading stimuli sequences from files in a future update (fingers crossed) - that and allowing the use (and extension) of the "constrain" command in the loop's script.

    There was a recent post by Sebastiaan describing a solution using Javascipt to present images or sounds from a URL: I wonder whether this kind of solution may possibly also be adapted to read from a csv file and posted the question. I don't have the Javascript expertise to solve that one. Hopefully someone out there can...


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