How to make a disc stimulus flicker

Samy Rima's Avatar

Samy Rima

31 Jan, 2018 04:41 PM

Hello,
I would like to present 2 discs that flicker at different frequencies. Could you advise me on how to go about this?
Thank you

  1. Support Staff 1 Posted by Christopher Sta... on 01 Feb, 2018 03:31 PM

    Christopher Stawarz's Avatar

    Hi,

    Can you be more specific? By "flicker", do you mean you want the disk to disappear and reappear repeatedly, or do you want it to change color? What are some specific on/off cycles that you'd like to use (e.g. 200ms on, 100ms off)?

    Thanks,
    Chris Stawarz

  2. 2 Posted by Samy Rima on 01 Feb, 2018 04:37 PM

    Samy Rima's Avatar

    Hello,
    I would like it to switch between black and white. I would like one disck to flicker at a 100 Hz and the other at 150 Hz fro example.
    Thanks for your help

  3. 3 Posted by Michael Schmid on 02 Feb, 2018 04:17 PM

    Michael Schmid's Avatar

    Hi Chris
    We'd like to connect to a ProPixx projector that according to specs can go up 1440 Hz refresh rate. Is there any experience whether mworks can handle this?
    If so then we would like to modulate the luminance of a disk at 65 Hz which is known as frequency tagging in EEG/MEG. We are at present playing with the Live Queue command to see whether this does the trick. Or is this the wrong way to think about it?
    Thanks, Michael Schmid

  4. Support Staff 4 Posted by Christopher Sta... on 05 Feb, 2018 07:25 PM

    Christopher Stawarz's Avatar

    Hi Michael,

    We'd like to connect to a ProPixx projector that according to specs can go up 1440 Hz refresh rate. Is there any experience whether mworks can handle this?

    I've never tested MWorks on a display with a refresh rate that high. I think it's very unlikely that the GPU would even come close to keeping up with 1440Hz, even on a Mac Pro.

    However, 65Hz should be no problem. 100-150Hz may be possible, too, depending on the GPU.

    If so then we would like to modulate the luminance of a disk at 65 Hz which is known as frequency tagging in EEG/MEG. We are at present playing with the Live Queue command to see whether this does the trick. Or is this the wrong way to think about it?

    If you need precise, frame-level timing, then the frame list stimulus is the right tool for the job. You give it a set of stimuli (as a stimulus group), and the frame list displays one per frame, optionally looping through the list indefinitely. I've attached a simple example, which presents a disk that flickers at the native refresh rate of the display.

    It's also possible to use a frame list to make the disc flicker at a non-native refresh rate. To accomplish this, you'll need to add multiple copies of the black and white discs to the stimulus group. For example, to produce a flicker at one third the native refresh rate, the stimulus group must contain three white discs, followed by three black discs.

    Will you need to vary the flicker rate at run time (e.g. on a per-trial basis)? That would be trickier, but we may be able to come up with a solution.

    Cheers,
    Chris

  5. Christopher Stawarz closed this discussion on 07 Mar, 2018 02:52 PM.

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