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Asked: 2026-06-12T07:47:52+00:00

I’ve managed to install the psychtoolbox-3 from the NeuroDebian repository without any explicit errors,

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I’ve managed to install the psychtoolbox-3 from the NeuroDebian repository without any explicit errors, but running AssertOpenGL yields this very verbose error message.

My system specs are as follows: Intel-based PC with Ubuntu 12.04 LTS

I’ve tried adding ~/Documents/MATLAB and all it’s subdirectories to the Matlab pathdef, as this is where I pointed the DownloadAdditionsForNeuroDebian function to. Similarly, I’ve tried adding /usr/share/octave/site/m/psychtoolbox-3/ and it’s subdirectories to the matlab path as well.

The error seems to be originating from a failed call to Screen; according to the above error message, Screen can’t be found. That having been said, I’m able to run Screen at the Matlab console, although I get this error:

>> Screen

In place of the expected mex file this placeholder file was executed:

  Screen

This mex file seems to be missing or inaccessible on your Matlab path or it is dysfunctional:

  Screen.*

Hmm. I cannot find the file on your Matlab path?!?

One reason could be that your Matlab path is wrong or not up to date
for the current Psychtoolbox. You may want to run SetupPsychtoolbox to 
fix possible path problems.

??? Error using ==> AssertMex at 210
Missing or dysfunctional Psychtoolbox Mex file for this operating system. Read the help text above carefully!!

Error in ==> Screen at 161
AssertMex('Screen.m');

Running SetupPsychtoolbox yields an error that is very similar to the first one.

I tried installing the suggested packages, but they were all already installed — nothing seems to work.

I have absolutely no idea where to go from here. Does anyone have any suggestions?

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1 Answer

  1. Editorial Team

    The SetupPsychtoolbox command seems to have a bug. What is happening for you (and for me, when I tried this) is that the folder containing Screen.mex is being placed at the bottom of the search path. Here’s how to fix;

    type “pathtool” at the Matlab commandline

    find the PsychtoolboxAddons entry and move it to the top (for me this was /usr/share/psychtoolbox-3/PsychtoolboxAddons)

    If you don’t have a folder PsychtoolboxAddons you may need to follow the instructions at http://docs.psychtoolbox.org/DownloadAdditionsForNeuroDebian

    Don’t forget to move your personal Matlab directory to the top also (the SetupPsychtoolbox command moves your personal directory to be underneath it’s directories, which is a bit mean).

    Save the path. Don’t ever run SetupPsychtoolbox again!

    Good luck!

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