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Forum Newbie
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Last Login: 10/17/2009 12:05:09 PM
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Hi,
I'm using E-prime for fMRI study for the first time and just want to confirm a few stuff.
1) I want to make sure that the time at which the trials are being presented in E-prime is as close as possible to the actual scanner clock time.
2) I want to make the delay between presentations as similar as possible across trials.
Could you advise on how I can achieve this?
Thank you,
pstnewbie
-- kc --
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Forum MVP
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Study Chapter 3, "Critical Timing", of the User's Guide that came with E-Prime. Don't do anything else until you do that.
-- David McFarlane, Professional Faultfinder
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Forum Newbie
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Last Login: 10/17/2009 12:05:09 PM
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Hi David,
Thanks..I had a look. It mentioned about cumulative mode vs event mode for timing mode. I'm still wondering which to use, since I want to have a fixed delay between presentations, and I want the trials not to deviate too far from the onset..
Please advise further?
Thanks
-- kc --
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Forum MVP
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Last Login: 5/14/2012 4:43:58 PM
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fMRI makes this decision easy. Since you must keep your task synchronized with the scanner throughout the run, you must use Cumulative Mode, period. (That is, unless you have some hardware mechanism to repeatedly resynchronize your task with the scanner throughout the run, which is almost never the case, and would require some additional programming footwork.) Strictly speaking, you only need Cumulative for objects active during the run, the rest can still be Event. But that is just too much for most folks to remember, so I tell fMRI researchers here to always make everything Cumulative. And because every object that you add in E-Prime defaults to Event Mode, that means that you must manually change each and every object to Cumultive, sigh. So just get in the habit now.
And you will of course still test the timing of your task against the scanner clock to be sure. And if you find that your E-Prime clock runs at a slightly different rate than the scanner clock, you can always adjust the EP clock by using Clock.Scale in your task program (see the Clock.Scale topic in the online E-Basic Help).
-- David McFarlane, Professional Faultfinder
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Forum Newbie
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Last Login: 10/17/2009 12:05:09 PM
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Thanks David.
I've done that for my experiment. Noticed some longer delays..any way I can reduce the duration of such delays?
-- kc --
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Forum MVP
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Last Login: 5/14/2012 4:43:58 PM
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Well, that all depends on your specific experiment, which means that it goes beyond what we can do in a general forum like this. So at this point I have to leave you with the same general advice that I give to others: you need to hire a skilled professional to help guide you through this (don't just take my word on this point, see sec 4.1.1 in the User's Guide). And just one more bit of advice...
pstnewbie (10/15/2009)
I had a look.
You need to do a lot more than just have "a look" at chapter 3. You need to thoroughly study it. Give it no fewer than five complete readings, working through the examples each time until you thoroughly absorb its content. Then you will be just at the bare beginning of understanding how to do critical timing.
-- David McFarlane, Professional Faultfinder
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