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Do you need to send stimulus triggers from PsychoPy when running EEG study?

I have a question about running EEG research, which I’m new to. I am working with a few other researchers to set up a new EEG study where we’ll basically show people images and ask them to make keypresses using PsychoPy. We are also going to record EEG data using Emotiv EPOC headsets. I’ve been trying to convince my colleagues that we should try to get 2 computers connected via a parallel or serial port so we can send triggers from PsychoPy to the EEG software automatically when an image is shown, which will be recorded at the exact time the image actually appeared in the EEG data.
However, I’ve now been told that this is not how they normally run things. Instead they present the stimuli and record the EEG on separate computers and do not send any triggers at all. Instead they match the stimuli to the EEG manually, and in some cases time the stimulus presentation using a stopwatch. Is this normal practice?

In my eyes this will lead to inaccurate results as we cannot be 100% sure that the data we analyse belong to the trial we think, as we might be slightly off in matching the stimuli to the EEG. However, I’m not sufficiently experienced in EEG to confidently say that their method is not ok.

Can anyone offer any advice on this?


This almost seems like a parody post?

No that wouldn’t be normal. Yes, you should send triggers, and they should ideally be timed to exact onset of the stimulus display (this can be done in PsychoPy code by using the .callOnFlip() function of the visual.Window class).

Thanks for the response, Michael. Unfortunately this is not a parody post but a situation I’m dealing with right now.

That was kind of my though as well as I’ve worked with fMRI and know how important stimulus onset timings are in neuroscience research. It’s just difficult to argue with people who have claimed to do this before while I’ve never used EEG in my own research previously.

I guess I’ll have to make a stronger case to invest the necessary time to set this up properly!

Good luck. By comparison, fMRI is MUCH more tolerant timing-wise than EEG, given it’s own much lower time resolution.

Hey, how do we send trigger for each stimuli in the builder view?

Assuming that you are using parallel port triggers, insert a component for one of those with the same onset time as the corresponding stimulus.

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Hi @Michael Could you please elaborate. I have just begun using PsychoPy.

Look in the component panel on the right side of the Builder window. You might need to click on the “I/O” tab to make the parallel port component visible. Click it to insert like any stimulus component.

I can’t advise on the content of that component: the value that gets sent and the duration of the pulse depends on your particular EEG hardware/software. The manual for that should tell you what the communication protocol. You also need to select what the parallel port address is on your PC (the one running PsychoPy). You’ll need to Google for how to that (I’m a Mac person, I’d need to Google it myself).

Thank you. The device is Cyton biosensing board. Any idea about how to trigger?

Hello, I was reading your post about emotiv EPOC EEG. How do you solve the problem? Thak you.