Stimuli/ Triggers/ Timing difficulties

[David McFarlane]

Any local electronics expert can handle this for you, you would do 
best to find one at your own institution.  Also, PST Web Support 
might have some advice.  One hurdle I will mention -- peak light 
output of modern LCD/TFT displays is much less than the old CRT 
displays, so if you use an LCD display then you will need a good 
sensitive photodetector.

-- David McFarlane


At 5/18/2012 11:46 AM Friday, Douglas wrote:
>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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