Time Lag between stimulus and trigger

Builder
1

Hello everyone,
I am having slight trouble in sending trigger via parallel port.

I am currently using;
OS Windows 11 Pro
PsychoPy version 2023.2.3
Standard Standalone

What are you trying to achieve?
The psychopy on my desktop is connected to EEG and electric stimulation device via a parallel port. I am attempting that there are triggers that are sent to EEG and electric stimulation device every time there is a new word that flashes on the screen, via loop.

What did you try to make it work?
I am able to achieve triggers in EEG, where different triggers are coming for fixation and word (stimulus) although there is significant lag (2 sec) while sending/receiving trigger by the stimulation device and hence the electric stimulation is not given when the word is presented.

What should I do?

2

What EEG system are you using?

Depending on what manufacturer your EEG system is from, it is possible they have alternate ways to signal the EEG system with less latency.

If that’s not the case, then the next easiest approach is to use a photocell or diode and have that output to a trigger that the EEG system can read. You could make your own out of maybe $100, but companies like Cedrus (StimTracker) make them turnkey for obviously considerably more.

3

Hi,
Sorry for the misunderstanding. The EEG signals are in sync with stimulus, its the electric stimulation that’s lagging by 2 seconds.

4

Ah. Okay - that makes sense.

Is the lag the same every time? If so I could imagine two possibilities:

If you had the parallel port signal to the stimulator sent during the fixation (or a blank stimulus before the word) and the fixation was 2 seconds before the word, that might be the easiest thing.

Additionally, our TMS systems have ways of adjusting the onset of the pulse based on when the trigger is sent via serial port. So if the lag is on the stimulator itself, perhaps there’s an adjustment there.

5

Right, so it looks like there is a delay in visual presentation through GUI of change in the state of stimulation. Otherwise, we can feel the current on time of stimulus presentation.

I am currently facing difficulty in sending multiple triggers to EEG (fixation, stim_on and stim_off) while turning the tes system on/off via those triggers for fixation (always off) and randomly for each stimulus (maybe on/off).
I am stuck at stim_on (for all stimulus presentations) and stim_off (for all fixations).

Any links/suggestions would be of huge help.

6

Ah yes, the multiple triggers at the same time to multiple devices is a common struggle.

We’ve had luck sending events to multiple devices in time with a parallel cable splitter (Amazon.com: CablesOnline 8 inch DB25 Parallel Male/Dual Female Y-Splitter Printer Cable (YS-005) : Electronics). Would something like that work for you?

7

Yeah, we have a parallel port like you suggested but I am struggling with how to build a three trigger design, where 2 triggers are off (for no stimulation during text-A2 and fixation-B1) and 1 trigger is on (for stimulation during text-A1).

8

So, we were able to resolve this by using the code component instead of parallel port component and defining triggers there.

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