synchronized trigger and stim presentation

[David Hairston]

Thanks Leisha. Maybe I should clarify. 

We need the trigger data on-line, so that it can be recorded along with
MEG data during acquisition. This makes it convenient for analysis
later, so that we can re-align trials according to stimulus onset, etc.

Hence, it is very important that the trigger be an accurate reflection
of the actual onset.

After some discussion with a colleague, if there is not a simple way to
do it via E-prime that is reliable, I'm considering using feedback from
a photo-diode system for the trigger.

Of course, getting a similar feedback from sound presentation seems even
more difficult, so I'm open to suggestions on that one, too...

 

Thanks,

Dave

 

 

________________________________

From: eprime at mail.talkbank.org [mailto:eprime at mail.talkbank.org] On
Behalf Of Leisha Wharfield
Sent: Monday, June 19, 2006 11:51 AM
Cc: eprime at mail.talkbank.org
Subject: Re: synchronized trigger and stim presentation

 

Doesn't standard data logging give you the precise timing of stimulus
presentation already, with its many time measurements? You can use
PreRelease to minimize OnsetDelay, and you can also set a
CustomOnset/OffsetTime. It's all in the Critical Timing chapter.

Leisha Wharfield
Decision Research
Eugene, Oregon USA

David Hairston wrote:



I need to send a trigger signal denoting the exact time of stimulus
presentation (assuming parallel port is the easiest method).

Here is the problem/question - in the event of, say, a visual stimulus,
what is the best way to get these as close in sync as possible? I could
have an inline code sending the trigger directly prior to an
ImageDisplay... but then it wouldn't it at least have the delay
associated with waiting for the next screen update (could be up to 9ms
if 100hz monitor)?. Or - what about putting the inline right after said
presentation - would it actually occur immediately (like w/in a few ms)
afterwards?

Or - is there a way to do it with a Slide object?

Unfortunately, this will be very difficult to test out empirically...

 

W. David Hairston, Ph.D.

ANSIR Lab

Dept of Radiology

Wake Forest University School of Medicine

Medical Center Blvd

Winston-Salem NC 27157

(336) 716-7160 (Offiice)

(446) 716 0798 (Fax)

 

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