Prerelease and data logging

[Cecilia Westbrook]

Hi all,

I'm sure this is covered in another thread, but I was not able to find it with searches. I'm using E-Prime for an fMRI task with critical timing. I'm using prerelease for my stimuli, but I'm seeing some weirdness in my data logging files. For stims with 200ms prerelease, it seems like it is logging them as the onsettime + 200ms. Shouldn't it be -200ms?

I see this in two ways: 1) if I look at the onsettime and the offset time and subtract them to get a duration, it is 200ms SHORTER than it should be (seems like it should be 200ms LONGER). 2) If I log the offsettime of the stim immediately preceeding it, the onsettime is 200ms later (even though it should be displaying at the same time as the offset time of the previous stim, right? +/- a little bit of delay in offsettime - but not 200ms of delay, surely?).

What is going on? Does anybody have any advice? Is the most accurate thing to do to just use the offsettime of the preceeding stim?

Thanks,

Ceci

[Paul Groot]

Hi Cecilia,

You may find one of David's post very informative:

https://groups.google.com/d/msg/e-prime/OeiZ00V9SRc/Vt2QAt3uoOcJ

Also note that the prerelease time of an object is used to prepare the following object. (This is something that is often overlooked.) 

Paul

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[Cecilia Westbrook]

Thanks, this is helpful.

One question that I still can't seem to find the answer for, though, is: what does E-Prime log as OnsetTime for an object set with pre-release? Does it log when the object starts drawing, or when it actually displays?

[Paul Groot]

from http://www.pstnet.com/support/kb.asp?TopicID=3025

Lastly, it is also important to keep in mind exactly what the Onset Time property is telling you. The Onset Time property will give you a timestamp of the exact time in which the display began to draw.

But you will find more relevant pages when you use keywords as eprime, onssettime, LCD, etc.

So, the OnsetTime has no direct relation with the time that E-Prime is preparing the stimulus in memory during the pre-release time of the previous object. 

Note that the actual pixel responses depend on the hardware that is being used, and the pixel location on the display. If it is really critical, you should check the real onsets using a light sensor and oscilloscope.

Paul

To view this discussion on the web visit https://groups.google.com/d/msgid/e-prime/817cc9c2-bcd9-446c-9748-8373ae375c6e%40googlegroups.com.

[Cecilia Westbrook]

Hi Paul,

Thanks, this makes sense now that you point it out to me.

I still can't figure out, then, why the onsettime would be 100ms later than the offsettime for the previous stimulus, if the stimulus is prereleased and therefore preparing in the background. There are not 100ms of blank screen when I do the task.

[Cecilia Westbrook]

Ah, I think I figured it out. Looks like the offsettime is actually 100ms early due to prerelease of the next stimulus.

[David McFarlane]

Ceci,

Looks like you got it. And if you log the StartTime for the object
that follows the 100 ms PreRelease, you should find that it is close
to the OffsetTime of the previous object. So if you have something like

FixationText (PreRelease=100)
StimImage

then the 100 ms PreRelease time of FixationText is taken up with the
time used to run any code between FixationText.FinishTime and
StimImage.StartTime (e.g., loading image files), and StimImage just
sitting idle until StimImage.OnsetTime. (StimImage.OnsetTime will of
course follow StimImage.TargetOnsetTime, with potential delay added
for screen refresh synchronization.)

BTW, in general if you use any PreRelease at all, then you might as
well make it large, e.g., same as Duration (and in fact this has
become the default behavior since EP2.0.10). At the same time, using
PreRelease does run the risk of other "gothchas" with regard to using
and logging responses that happen during the PreRelease period, but
EP2.0.10 also adds specific safeguards to help with that.

-----
David McFarlane
E-Prime training
online: http://psychology.msu.edu/Workshops_Courses/eprime.aspx
Twitter: @EPrimeMaster (https://twitter.com/EPrimeMaster)

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At 6/5/2014 03:39 PM Thursday, Cecilia Westbrook wrote:
>Ah, I think I figured it out. Looks like the offsettime is actually
>100ms early due to prerelease of the next stimulus.
>
>On Thursday, June 5, 2014 1:21:10 PM UTC-5, Cecilia Westbrook wrote:
>Hi Paul,
>
>Thanks, this makes sense now that you point it out to me.
>
>I still can't figure out, then, why the onsettime would be 100ms
>later than the offsettime for the previous stimulus, if the stimulus
>is prereleased and therefore preparing in the background. There are
>not 100ms of blank screen when I do the task.
>
>On Thursday, June 5, 2014 5:00:30 AM UTC-5, Paul Groot wrote:
>
>from

><http://www.pstnet.com/support/kb.asp?TopicID=3025>http://www.pstnet.com/support/kb.asp?TopicID=3025

>
>Lastly, it is also important to keep in mind exactly what the Onset
>Time property is telling you. The Onset Time property will give you
>a timestamp of the exact time in which the display began to draw.
>
>But you will find more relevant pages when you use keywords as
>eprime, onssettime, LCD, etc.
>
>So, the OnsetTime has no direct relation with the time that E-Prime
>is preparing the stimulus in memory during the pre-release time of
>the previous object.
>
>Note that the actual pixel responses depend on the hardware that is
>being used, and the pixel location on the display. If it is really
>critical, you should check the real onsets using a light sensor and
>oscilloscope.
>
>Paul
>
>
>
>On 5 June 2014 00:16, Cecilia Westbrook <ceci.we...@gmail.com> wrote:
>Thanks, this is helpful.
>
>One question that I still can't seem to find the answer for, though,
>is: what does E-Prime log as OnsetTime for an object set with
>pre-release? Does it log when the object starts drawing, or when it
>actually displays?
>
>On Wednesday, June 4, 2014 2:47:11 PM UTC-5, Paul Groot wrote:
>Hi Cecilia,
>
>You may find one of David's post very informative:
>

><https://groups.google.com/d/msg/e-prime/OeiZ00V9SRc/Vt2QAt3uoOcJ>https://groups.google.com/d/msg/e-prime/OeiZ00V9SRc/Vt2QAt3uoOcJ