single refresh display duration - help?

[Paul Groot]

Well, since you already tried several configurations, this might be a
non-trivial issue which is hard to track down without having the
script itself... Did you also check the Timing Mode of the objects?
You probably would like to set this to 'Event' (the default). THe sync
options should also be kept to their default values (onset=vertical
blank, offset=none). WHich EP version are you currently using? And did
you also run the RefreshClockTest?
(http://www.pstnet.com/support/kb.asp?TopicID=3003)

PST also offers an alternative pre-load technique for slides which
doesn't require the use of canvases:
http://www.pstnet.com/support/samples.asp?Mode=View&SampleID=23

However, I would probably try to start from scratch and only use empty
Text objects and set all pre-release times to the max. values. If this
works, you can replace the text objects with (empty) slides. Then add
input masks. Then add images. And so on...

best,
Paul


2012/3/6 liwenna <liwenna at gmail.com>:
> Thanks Paul for that thorough reply!!
>
> Unfortunately I did all that (and more ;)) but to no avail. The
> display that follows the 13ms display is actually empty, except for a
> backgroud color (gray shade). I tried using wait objects and text
> display's rather than a slide display, and also the offscreen
> canvasses. With offscreen canvasses the problem lies no longer with
> the 'empty display that overlays the 13 ms image' arriving too late,
> the timing is the fine in about 75% of the trials, but I am pretty
> certain that the 13ms display is skipped in about 25% of the trials.
>
> The graphics card might be crappy, I am also a bit suspicious
> regarding the display that I was assigned for this project,
> nonetheless, the 'old task' seems to be work well on it, while this
> new taks also does not perform well on the pc & display that I used
> for the old project (and do trust).
>
> It simply drives me crazy that the exact same set-up in terms of
> settings that are known to matter for timing, works perfectly in one
> set-up (with more images and a more difficult list structure, even
> with an additional procedure that has a 27ms display added to the
> sequence with the 13 and 496 display) and just doesn't work in the
> simpler set-up. Something must somehow matter that I completely
> overlook.
>
> I suppose I'll spent the second part of this afternoon on it again:
> any additional advices are more than welcome :)
>
> best,
>
> liw
>
> On 5 mrt, 21:23, Paul Groot pfc.gr... at gmail.com> wrote:
>> Hi Anne-Wil,
>>
>> You will get the best onset performance if you:
>>
>> 1) set the pre-release time of the objects before both slides to the
>> maximum possible value (i.e. same as duration of that object). In
>> other words: if the 13ms slide is displayed immediately after the
>> other slide, you must set the pre-release time of the first slide to
>> 496 (or 500 if you apply point 3 below).
>>
>> 2) Use bitmaps instead of JPEG and make sure the color depth is the
>> same as used in your exp. This might help because decoding jpeg files
>> takes a lot of CPU time (although the smaller jpeg files will load
>> faster from disk.)
>>
>> 3) use durations which end in the middle of two screen refreshes I.e,
>> if the display is using a refresh rate of 75Hz, you will set the fast
>> stimulus to 0.5*1000/75=7ms, and the longer stimulus to
>> 37.5*1000/75=500). Not sure if this is still required with the new EP2
>> release, though...
>>
>> Depending on the hardware performance and screen resolution, this
>> still might be insufficient to get single frame stimuli. If this is
>> the case, you might want to prepare the stimuli using off-screen
>> canvases at the start of the sequence and copy to the display canvas
>> using a fast copy at the vertical blanking interval. This should
>> always work, unless the graphics card is crappy.
>>
>> best,
>> paul
>>
>> 2012/3/5 liwenna <liwe... at gmail.com>:
>>
>> > Hi all,
>>
>> > I have something and I hope someone may have experienced a similar
>> > thing that may help me out on this one.
>>
>> > I have an experiment in which a sequence of displays occurs with the
>> > two most important display having durations of 496 and 13 ms
>> > respectively (give or take max 2 ms). Back then, it took me quite some
>> > work but in the end I got the timing right (yay).
>>
>> > Now... I am trying to build a second, similar but less complex, task.
>> > This new is less complex since it shows only a single. rather than
>> > multiple, image at the 496 ms display, and has a far less complex list
>> > structure due to less different procedures. However: I can not get the
>> > timing right at all..  the display that follows the 13 ms display just
>> > keeps being delayed by one refresh (13 ms).
>>
>> > I have tried pretty much everything for hours and hours:
>> > - building the new task from scratch, imitating all (or at least I
>> > believe so?) settings from the old (correctly timed) task (and then
>> > tweaking all the settings too)
>> > - modifying the correctly timed task into the new task  (and then
>> > tweaking all the settings)
>> > - using off-screen canvases rather than slides (but it seems that the
>> > 13ms 'canvas' is simply not shown in about 25% of the trials... which
>> > is not good enough either)
>>
>> > I believe I have covered pretty much everything that could be done
>> > about it, but I honestly fail to see why the old task would be timed
>> > correctly (still is!) and any attempt at the more simple task just
>> > fails in terms of timing.
>>
>> > I so very much hope that someone here is able to identify the one
>> > thing that I just keep overlooking? >.<
>>
>> > Best,
>>
>> > Anne-Wil
>>
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