EEG Pulse Duration with Onsetsignal

[David McFarlane]

Fair question.  But I will still give my stock reminder:  1) I do not 
work for PST.  2) PST's trained staff takes any and all questions at 
http://support.pstnet.com/e%2Dprime/support/login.asp , and they 
strive to respond to all requests in 24-48 hours (although current 
estimates are more like 10 days) -- this is pretty much their 
substitute for proper documentation, so make full use of it.  3) If 
you do get an answer from PST Web Support, please extend the courtesy 
of posting their reply back here for the sake of others.

On top of that, I will tell you to not take my word for 
this.  Ideally, you will hook up a voltmeter or oscilloscope to your 
paralell port and measure the actual duration of your "pulse".  That 
would settle the question.

But now my answer.  E-Prime will set the OnsetSignalPort to the value 
in OnsetSignalData at the onset time of your Slide object.  That 
value will remain on the port until it is replaced with something 
else.  In particular, EP will set the OffsetSignalPort to the value 
in OffsetSignalData at the *offset* time of your Slide object; as 
long as OffsetSignalPort = OnsetSignalPort (and OffsetSignalData <> 
OnsetSignalData), this means that the "pulse" will last from the 
onset time of your Slide object until the offset time of the 
Slide.  Now note that the target offset time of your Slide will be 
onset time - PreRelease.  So, putting this all together, the pulse 
will last for more or less Duration - PreRelease ms, depending on 
onset and offset delays; if PreRelease = 0, then the pulse should 
last about Duration ms.

So let's illustrate this with some numbers.  You have 
Slide.OffsetSignalPort = Slide.OnsetSignalPort, Slide.OnsetSignalData 
= 5, Slide.OffsetSignalData = 0, Slide.Duration = 1500, and 
Slide.PreRelease = 0.  In this case, the value 5 should go out to the 
port and stay on for more or less 1500 - 0 = 1500 ms (depending on 
onset & offset delays), and then go to 0.  If you set 
Slide.PreRelease to, say, 1400, then the pulse will last more or less 
1500 - 1400 = 100 ms.  (We do exactly this sort of thing to 
manipulate pulse durations in our programs, but before you mess with 
PreRelease please note carefully the caveats in Chapter 3 of the User's Guide.)

I hope this helps.

-- David McFarlane, Professional Faultfinder


>I am trying to clear something up.  Right now I am sending triggers to
>Biosemi via parallel port using the onsetsignal and offsetsignal
>commands.  Please do not tell me to read the documentation on such and
>such! I have done so...
>
>So here is the situation:
>In one instance, trigger 5 is sent at the onset of the presentation of
>a text slide (which is synced to the vertical refresh of the monitor,
>with a refresh rate of 85hz).  The slide is displayed for 1500ms.
>On the offset of the slide (after 1500ms) the offsetsignal sends
>trigger 0 to clear the port.
>
>My question then is how long is the duration of the pulse sent to
>Biosemi? Is it 1500 ms, or is it the pulse duration equivalent to the
>refresh rate of the monitor (11.76ms)? Or something else...?

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