synchronized trigger and stim presentation

[Don.Rojas at UCHSC.edu]

Dave,
 
Use the onsetsignal enabled property of the stimulus to send your
trigger.  We use a photo-diode in addition to that to adjust the timing
jitter on the LCD projector.  The photo-diode won't give you multiple
trigger codes without a lot of painful hardware tinkering, but you can
probably use whatever software you have offline to combine the e-prime
trigger and the photo-diode signal to achieve what you need.  What MEG
system do you use?  If you have a 4D Magnes system, I can probably be of
further help to you with respect to the latter suggestion.
 
Donald C. Rojas, Ph.D.
U. of Colorado Neuromagnetism Lab
Denver, CO USA

	-----Original Message-----
	From: eprime at mail.talkbank.org [mailto:eprime at mail.talkbank.org]
On Behalf Of David Hairston
	Sent: Monday, June 19, 2006 10:35 AM
	To: Leisha Wharfield
	Cc: eprime at mail.talkbank.org
	Subject: RE: synchronized trigger and stim presentation
	
	

	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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