problem with short ISI

[David McFarlane]

Susie,

Thanks for all the wonderful detail, I wish I had a good answer for 
you!  Just a couple thoughts...

First, can you add a PreRelease to the first sound object?  That 
might allow some time for your ISI blank screen to get set up (I 
don't think the PreRelease on the second sound object does anything 
for you).  Do keep the PreRelease on your ISI as long as 
feasible.  (When I use PreRelease I usually go ahead and make it as 
long as the Duration, or even longer, say 10000.  It doesn't seem to 
matter (short of terminating with a response, etc.), which makes 
sense if you think about what PreRelease really does under the covers.)

Second, as you remember from Chapter 3 of the User's Guide, take a 
look at the Onset and Offset Sync of your ISI blank screen.  If you 
sync with the vertical blank then you will have delays due to waiting 
for the screen to refresh, so you may want to turn that off.  OTOH, 
without syncing to vertical blank you may get brief visual artifacts 
as your blank screen goes on or off.  Just an unavoidable limitation 
of our current technology.

-- David McFarlane, Professional Faultfinder


>I have a vowel discrimination task (vowels are 50 ms each) that I've
>been presenting at several ISIs (as low as 40 ms and as long as 1500
>ms). All of these ISIs have been correctly logged (subtracting slide
>onset of the blank screen from the onset of the second vowel).  I have
>it set up to play a sound object, have a blank screen for the duration
>of the specified ISI, and then the second sound object. (I have the
>ISI blank screen set to preload at 100 ms and the sounds are set to
>'streaming'. Also, I'm running 2.0 Pro on an XP machine). When I
>changed the duration of the blank screen to 10 ms I got actual
>durations from 27 to 40 ms. I've tried adding a preload of 50 to the
>second sound object and have also tried to reduce the preload on the
>blank screen to 50 ms and these have not helped.
>
>Thanks in advance!
>Susie


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