Stimuli & Response Trigger Interference

[Courtney]

I am desperate at this point. I have tried several different ideas and none of them have worked. I am using E-Prime 2 for an EEG study where triggers are to be sent from the stimuli computer to a computer using BrainVision software via parallel port.

I have two tasks, one visual and one audio. The both have 4 stimuli categories and both are response-based tasks. I am trying to program the task as such that there are 4 separate stimuli onset triggers, one for each category (S1-S4). For the visual task, the participant responds with either "1" or "9" and I would like a response trigger to reflect correct or incorrect response (R1, R2). For the audio task, the participant respond by pressing SPACE only on occasions that they hear one particular tone (out of 4 categories of tone types). I want to program it so that there are 4 separate stimuli onset triggers, one for each category and response triggers for correct or incorrect. In the audio task, omitted response could be considered correct or incorrect depending on the trial. 

My problem is this: there seems to be some interference between stimuli and response triggers. They won't work properly and often overlap. This is the case regardless of if I use Task Events or try to use InLine Script or if I try to use a combination of the two. The stimuli triggers for the audio task are especially challenging. Often it simply will not record response triggers, or simply not consistently and now the stimuli triggers will come up but not when there are repetitions. For example, if there is a standard tone (S1) followed by five more standards, it will only send one S1 trigger and will not send another stimuli trigger until a different category trial comes up. 

I have tried different methods I have found suggested on PST website and again, no luck. I am very much at a loss and I really don't know how to proceed or what else I can try at this point. If anyone has run into this or has any other ideas, please please let me know. I would be very grateful.

Courtney

[McFarlane, David]

Courtney,

Does your program make sure to reset the parallel port (LPT) output to 0
before outputting each trigger? Can you verify this in the EEG record?

How much time does your program allow between resetting the LPT output
and outputting the trigger?

How long does each trigger last before you reset the LPT output to 0?

-- David McFarlane

(In case anyone wonders, "LPT" stands for "line printer", and goes back
to the days when the parallel port was used primarily for high-speed
communication with a *line* printer, a fancy mechanical device that set
up and printed one entire line of print at a time -- look that up on
Wikipedia!)

[Courtney]

Hi David,

Thank you for responding. Is the LPT reset done through InLine script or is it done using task events or do I need to go through device manager for either the experiment or the computer? Now that you mention it, it doesn't look like it is resetting. I'm having difficulty narrowing down just how long before it resets.

Courtney

[McFarlane, David]

Courtney,

I go over this in a lesson in my online E-Prime 2 course. You might
consider taking that. Note, however, that the course videos predate
Task Events, so they show how to handle EEG markers/triggers using
WritePort and OnsetSignal in inline script instead, with a little bit of
text about Task Events to supplement the video.

As I explain there (and have done elsewhere in this Group), you must
reset the LPT output before presenting any new output. Typically you
would do that with a mechanism that mirrors how you present the
marker/trigger itself -- WritePort, OnsetSignal, or OffsetSignal in
inline code, or Task Events (note that you can add multiple Task Events
to a single object, with different delays, just think how you could use
that). I am pretty sure that we have fully covered this in a thread
sometime in this Group, but I don't have a link handy -- if you search,
you should find a good thread, and if you do then please post the link
here for others :) .

-- David McFarlane

[Courtney Lord]

You're my hero David. I'll search the other threads some more and let you know how I make out.

Thank you again,

Courtney

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[Courtney]

You're my hero David. I'll search the other threads some more and let you know how I make out.

Thank you again,

Courtney