Stimuli/ Triggers/ Timing difficulties

[Douglas]

Hello again Mr. McFarlane,

I want to use Photodiodes.
Would you please tell me what kind of photodiodesI have to buy and how
I should install it?!

Thanks

On Apr 20, 12:12 pm, David McFarlane <mcfar... at msu.edu> wrote:
> First, I must ask how exactly you measure "Stimulus OnsetTime" and
> "Trigger OnsetTime", please provide details.  AFAIK EP does not log
> those separately, so you seem to know something that I do not.
>
> But ultimately, if you really want to know the relationship between
> the time of a visual stimulus and the time of a trigger output, then
> you must get out a dual-channel oscilloscope, aim a high-speed
> photodetector (e.g., photodiode or phototransistor) at your display
> screen, tap a line into your trigger output, and then look at those
> signals on the oscilloscope.  You might need to find someone local
> with some electrical engineering experience to help with this.
>
> And then, to get the best timing performance, you *must*, MUST
> thoroughly study Chapter 3 of the User's Guide that came with
> E-Prime!!!  I cannot stress that enough!  Until you do that, you
> might as well be using a handheld stopwatch.
>
> -----
> David McFarlane
> E-Prime training
> online:  http://psychology.msu.edu/Workshops_Courses/eprime.aspx
> Twitter:  @EPrimeMaster (twitter.com/EPrimeMaster)
>
> At 4/20/2012 11:52 AM Friday, you wrote:
>
>
>
>
>
>
>
> >Hello David,
>
> >Thanks a lot for your help.
> >We made the PreRelease 400 and it seems like a miracles happened. Many
> >thanks to you.
>
> >Now, As our first problem was the delay of appearing the stimuli and
> >triggers. We realized we still have that Delay and that the delay is
> >not the same during the whole experiment among all Stimuli. As we read
> >your posts regarding the timings and delay. We have realized we might
> >have been measuring the delay in a wrong way. I am quoting what I read
> >with your signature and then I will ask you my new question!
>
> >"- OnsetTime:  Time when E-Prime actually submitted the stimulus data
> >for
> >    presentation (e.g., proceeded to copy data to display memory or
> >load
> >    sound buffer).  This may not coincide with when the stimulus
> >actually
> >    got presented, e.g., if data are submitted in the middle of a
> >display
> >    refresh cycle then they may not get presented until the next
> >refresh."
>
> >So, We have been trying to make the delay between the time stimulus is
> >Presented by E-Prime on the screen and the time Trigger appears,, as
> >least as possible and we wanted that delay to be fixes or within the
> >least range possible. But As we read your post, we realized that what
> >we were measuring which was the difference between Stimulus OnsetTime
> >and Trigger OnsetTime, is the wrong way to measure that delay.
>
> >Do you have any ideas  that what can we add in out inline to measure
> >this delay or where we should look if we want to see the time of
> >presentation of the stimulus and trigger?
>
> >Looking forward to hearing from you.

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