Bluetooth transmission lag and ERP experiments

PeterNocPeterNoc PeterNoc
edited April 23 in Cyton

Hi All,

I was going through:
BrainHack2020 EEGNotebooks

John Griffiths mentions that BT introduces 20-30 ms lag to the data acquisition.
Does this not bother people who run ERP experiments with Cyton/Ganglion ?
Is there a cable USB connection Project on the way somewhere ?

Peter

Comments

  • wjcroftwjcroft Mount Shasta, CA

    Peter, hi.

    Many ERP experimenters use some type of synchronized 'trigger' recorded signal, such as this tutorial:

    https://docs.openbci.com/Examples/VideoExperiment/

    Since the trigger is recorded exactly at the same time as the EEG channels, the Bluetooth or USB buffering has no impact.

    Although the link above uses Cyton, a similar trigger recording can be done with Ganglion, by using one of the 4 channels for trigger.

    Regards, William

  • PeterNocPeterNoc PeterNoc

    Thx William
    So You are saying that the stimulus signal and the EEG data is is not received from the receiver application which combines the real time stimulus and delayed EEG data but stimulus signal is the sent to the Cyton board which combines it into the EEG stream and sends to the receiver application all with exactly same delay (which does not really matter now) ?
    What is the name of the channel in the data transmitted from Cyton that contains the stimuli timing info ?
    How people combine this (hardwarewise) with systems like psychopy which is software runing on a computer and not a easily connected electronics board ?

    Regards
    Peter

  • wjcroftwjcroft Mount Shasta, CA
    edited April 22

    Did you READ the link I gave? The 'trigger' signal is recorded at EXACTLY the same moment in time as the relevant stimulus recorded with the EEG. The trigger is presented on the screen and sensed with a photodiode. A small square on the monitor screen is devoted to the trigger and the diode taped to that screen area. The visual stimuli are presented at the same instant that the trigger lights up. Other possible triggers can be used, see below.

    Cyton has three 'Aux' channels which can be configured to receive digital or analog signals in the 0 to 3.3V range.

    https://docs.openbci.com/Cyton/CytonSDK/#board-mode

    re: PsychoPy & parallel port triggers

    https://psychopy.org/hardware/parallelPortInstr.html

  • PeterNocPeterNoc PeterNoc

    Did read, although I missed the part with sticking the photodiode to the screen.
    Thx a lot for your help
    Regards
    Peter

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