Timing issues

[David McFarlane]

Kam,

Good, you worked through Chapter 3 of the User's Guide.  Next, 
supplement that with my explanation of EP time audit measures at 
http://groups.google.com/group/e-prime/browse_thread/thread/39e899d3457d4917?pli=1 
.  Then you will see that your results are exactly what you should 
expect.  In particular, regarding the points you want resolved:

(2) These all are about the same because, with PreRelease >= 
Duration, execution of the object ends as soon as possible after it begins.

(3) ISI.DurationError  =  ISI.OffsetTime + ISI.PreRelease - 
ISI.OnsetTime - ISI.Duration  =  t + 200 - t - 100  =  100.

(1) I don't know what makes your ISI.OnsetDelay drift "cyclical", but 
the drift itself simply results from natural delays in starting 
execution of ISI after ending exection of Stimulus.  Remember, a 
PreRelease may help reduce OnsetDelays in the *following* object, it 
has no such effect on the object that has the PreRelease.

That said, a few more comments:

- You correctly see that syncing with screen refresh almost never 
makes sense for auditory stimuli (I don't think PST explains this 
very well).  Corroborating this, the latest release of EP2 
(2.0.10.182) now corrects the default value of Onset Sync to (none) 
for SoundOut objects.

- You might think further about whether Event or Cumulative timing 
mode makes the most sense for your project.

- To get links for the Critical Timing example programs, submit a 
request to PST Web Support at 
http://support.pstnet.com/e%2Dprime/support/login.asp .

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

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At 6/11/2012 06:14 PM Monday, Kam wrote:
>Hi all,
>I'll try to be as brief as possible. I've already read CH 3 of the
>user's guide re: timing in e-prime. My question concerns why nothing
>to very little of the timing data output in my edat file makes sense
>in the context of CH 3.
>
>The experiment is a simple random presentation of sound files of
>moderately varying lengths, separated by a random interstimulus
>interval. The set-up includes a trial procedure with an inline that
>among other things defines a variable SOA set to 100 (for testing
>purposes) and the command c.SetAttrib "ISI", SOA to set ISI duration.
>Then the trial procedure proceeds with a (1) SoundOutObject called
>Stimulus with attributes {buffer size=800ms; buffer mode=streaming;
>start/stop offsets=0; loop=no; stop after=yes; end sound action=none;
>duration=800; timing mode=event; pre-release=0; sync onset/
>offset=none} and (2) pause command called ISI with attributes
>{duration=ISI (mentioned above); timing mode=event; pre-release=200;
>sync onset/offset=none}. Subsequently the trial procedure terminates
>having cycled through a stimulus list and the experiment concludes in
>a single Block List. So that is 3 hierarchical procedure levels in all
>{session, block, trial} with only 1 block of stimuli.
>
>In my data file what I can make sense of is:
>(1) Stimulus.Durations = 800 as defined in the Stimulus attributes
>(2) Stimulus.OnsetTime = Stimulus.Start time and occurs before (3)
>Stimulus.OffsetTime = Stimulus.FinishTime
>(4) Stimulus.DurationError = 0 considering Onset and Offset times
>occurred as expected
>(5) ISI.Duration = 100 as defined in my inline
>
>
>And what I cannot make sense of; I would appreciate if anyone can help
>me resolve:
>(1) There is a cyclical "drift" when I plot Stimulus.OnsetDelay
>irrespective of where I use a pre-release (ie., 100-200 msec in either
>the Stimulus or ISI-wait objects)
>(2) ISI.OnsetTime = ISI.Start time = ISI.OffsetTime = ISI.FinishTime
>(3) ISI.DurationError = 100
>
>Generally speaking, there is very little said about proper
>implementation of the SoundOut object, and the entire timing
>discussion revolves around display refresh rates, which I don't
>understand the importance of in a strictly auditory set up. Also, does
>anyone know the exact web address where I can download the critical
>timing eprime scripts mentioned in the user's guide?
>
>Thanks in advance
>Kam

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