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[solved] Detecting keypress is different in Psycho and Legacy mode?

edited January 2013 in OpenSesame


I run an experiment where subjects press lshift or rshift when they see a left or right arrow.
The loop definition includes

setcycle 0 correct_response "rshift"
setcycle 0 t1 "rshift"
setcycle 1 correct_response "lshift"
setcycle 1 t1 "lshift"

Then in keyboard response I define:

set allowed_responses "lshift;rshift"

In the logger I ask (among other things):

log "response_keyboard_response"

This works nicely in Legacy mode, but when I swith to Psycho mode (for more timing precision), both right and left key press are recorded as "lshift".

Is there anything I can change to fix this?

Thanks in advance


  • edited January 2013

    Dear Guido,

    The fact that right-shift key presses are coded as 'lshift' is a known issue, see this previous thread.

    Like you mentioned, this occurs only with the PsychoPy back-end (and solely when running experiments on Windows, on Ubuntu right-shifts are coded as "rshift"). It probably has something to do with low-level libraries this back-end uses for keyboard-response detection, and is therefore outside the control of OpenSesame. We will notify the developers of PsychoPy about it. For now, if running your experiment on Ubuntu or using different response keys is not an option, I would suggest the following:

    You mention that you're using the PsychoPy back-end to obtain more precise timing. In this case perhaps you could switch to the Expyriment back-end, which is the default back-end as of OpenSesame 0.27. This back-end has excellent timing properties too, and is in this sense equivalent to PsychoPy. And, importantly, it does detect right-shift key presses as "right shift".

    OpenSesame 0.27, the latest stable version of OpenSesame, can be obtained here:

    I hope this helps!

    Best wishes,


  • edited 10:40AM

    Dear Lotje,

    The experiment now works fine with the Expyriment Back End.

    Many thanks.

    Guido :\">

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