Synchronizing with Trigger Signal from MRI Scanner

[Paul Gr]

hello hilke,

In most cases fMRI-trigger signals are sent as a digital TTL-pulse, which 
can be detected by EPrime by using the parallel printer port (LPT port). The 
technique used by EPrime to collect trigger pulses is the same as collecting 
button box responses. You can find a description of this technique at 
http://www.psy.vu.nl/download/menu.  Anyway, you can synchronize your 
stimuli with these triggers by placing an EPrime wait object (or a blank 
text screen if you prefer) immediately before the image object. Then add the 
input device (probably a Port device) to the ‘Input mask device’ list 
(Duration/Input tab) and set the ‘Duration’ to Infinite and the ‘End Action’ 
to Terminate. When you use another input device type for collecting the 
trigger pulses (such as an SRBox device), then you should add this specific 
device to the list instead of the Port device. In some cases it is also 
advisable to configure the ‘Allowable’ property to the specific code you’re 
using (i.e. ‘5’)

Note that there will always be a small image onset delay error due to the 
asynchronous nature of the triggers. This is because the image is normally 
not shown before the next refresh cycle of the beamer/monitor after a 
trigger has occurred. When your script is configured properly then this 
onset error should always be less then the refresh interval time and will 
not be a problem in fMRI studies.

Best,
Paul.

Vrije Universiteit Amsterdam


>From: Hilke Plassmann <hilkep at stanford.edu>
>To: eprime at mail.talkbank.org
>Subject: Synchronizing with Trigger Signal from MRI Scanner
>Date: Thu, 11 May 2006 08:10:54 -0700
>
>Hi,
>
>I have a question concerning the use of e-prime for fMRI experiments.  I 
>would like to synchronize the ImageDisplay Onset with the trigger  signal 
>from the scanner. This signal is send via a response box I'm  using and is 
>coded as a '5'. That means that every 2secs (TR=2secs)  the scanner sends a 
>'5' to the PC in the control room which can  theoretically be detected by 
>E-Prime. Does anybody know how to tell  Eprime to use the Trigger Signal to 
>start the Image Display Onset? Or  to use the signal to adjust the timing 
>of the Eprime task? Many  thanks for your help.
>
>Hilke
>
>
>