Constant timing for targets

[Tony Zuccolotto]

Steve,
 
There are a number of ways to do this, but I think the easiest is to add
an Inline object after the stimulus presentation with the following
single line of script on it.
 
    ' Assume the object named Stimulus is presenting the stimulus and
enabling the response. 
    ' The Stimulus object should have ClearAfter=yes and OffsetSync=yes
(which are not the defaults)
    SetNextTargetOnsetTime (Stimulus.OnsetTime + Stimulus.Duration)    '
add Stimulus.Duration if appropriate or another value equal to the time
you want between stimulus presentations
 
The SetNextTargetOnsetTime command allows you to directly manipulate
when the next stimulus object to run should present it's stimulus.   The
Stimulus.OnsetTime property returns the time (in ms) when the stimulus
was actually presented.   Thus, if you use that time and add a duration
equal to an entire trial length then the next object to run (presumably
the Stimulus object of the NEXT trial) then your critical stimulus
should occur at fixed intervals.
 
Depending on the exact nature of your stimulus sequence you should
probably consider using Timing Mode=Cumulative (see the E-Prime
documention on Critical Timing), but if they only thing you have in your
trial is the Stimulus object itself then the above line of script
effectively simulates what the Cumulative timing mode is trying to do.
If you have a sequence like Fixation, Probe, Mask and you want to keep a
fixed trial duration and fixed inter-trial-interval then you should
really look into cumulative timing mode.
 
To verify the above script is working correctly I would make sure the
Stimulus object is logging OnsetTime and OnsetDelay and then use
E-DataAid to view those two columns.   Copy the data to Excel and
subtract the Stimulus.OnsetTime of trial n+1 from Stimulus.OnsetTime of
trial n, i.e. to compute the time between the stimulus presentations.
If things are setup correctly then these should times should be within 1
screen refresh of the desired duration.
 
Hope that helps.
Tony
*** DISCLAIMER: VIEWS EXPRESSED ARE MY OWN AND DO NOT NECESSARILY
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Anthony P. Zuccolotto 
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 -----Original Message-----
From: Steve Johnston [mailto:s.johnston at bangor.ac.uk]
Sent: Wednesday, July 03, 2002 5:04 AM
To: Eprime Maillist
Subject: Constant timing for targets



I've happily set up an experiment to show a stimulus to a subject, but
at the moment once the user responds the next sequence begins
immediately. What I was after was, once a target had been responded to,
an empty screen for the remainder of the period such that the period
between fixation points was a constant.
 
Does anyone know how to set this up? I have played with the various
settings but so far no joy.
 
Cheers
 
Steve Johnston

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