frequency of cursor position recording

[Ashtyster]

Hi David,

thank you very much for such a detailed explanation!
I'll follow your advice.

All best,
A.

On Mar 28, 8:26 pm, David McFarlane <mcfar... at msu.edu> wrote:
> Ashtyster,
>
> If I may jump in here...
>
> So, e.g., for a sampling rate of 50 Hz, you could use
>
> Sleep 20
>
> (i.e., same as your example), or, for slightly better documentation,
>
> Sleep 1000/50
>
> or, for even better documentation without "magic numbers",
>
> Const SampleRate_Hz as Long = 50
> Sleep 1000/SampleRate_Hz
>
> Now, I don't quite trust the Sleep command myself -- what happens if
> some process interrupts during the Sleep?  Then the effective
> duration of the Sleep will be a little longer, and with each delay
> things get more desynchronized (note that this acts exactly the same
> as E-Prime's Event timing mode, see Chapter 3 of the User's Guide
> that came with E-Prime).  If you need to keep things better
> synchronized (i.e., more like E-Prime's Cumulative timing mode), then
> you will have to roll your own delay loop, something like
>
> Const SampleRate_Hz as Long = 50
> Const tSample_ms as Long = 1000/SampleRate_Hz
> Dim  tDelay as Long
> tNext = Clock.Read  ' initialize *once* at the start of the sampling loop
> Do Until <condition to end sampling loop>
>      <record mouse cursor position>
>      tNext = tNext + tSample_ms
>      Do Until Clock.Read >= tNext
>          <stuff to do while waiting for the next sample>
>      Loop
> Loop
>
> Now the mouse cursor will be sampled on more or less exact 20 ms
> boundaries, with minimal drift.  Note that this method also does not
> completely stall your program in between mouse cursor samples.
>
> BTW, you can find the Sleep command, and much more besides,
> documented in the online E-Basic Help.
>
> -- David McFarlane, Professional Faultfinder
>
> At 3/28/2011 05:17 AM Monday, you wrote:
>
>
>
>
>
>
>
> >Hi Paul,
>
> >thank you for your reply.
>
> >So if I understand you correctly, I should just calculate temporal
> >resolution from the output, and adjust the sleep value according to
> >the temporal resolution I'd like to have?
>
> >All best,
> >A.
>
> >On Mar 25, 11:54 pm, Paul Groot <pfc.gr... at gmail.com> wrote:
> > > Hi Ashtyster,
>
> > > The sleep instruction simple puts the running script in 'idle'mode for
> > > the specified number of milliseconds. Windows can use this time to
> > > allow other processes to consume some CPU time. This construction is
> > > often used in loops to prevent the system to become stalled. A
> > > duration of about 20 milliseconds might be sensible on systems that
> > > are connected to a display at 50Hz. The value could even slightly less
> > > on systems with a typical refresh rate of 70-80Hz. However, windows
> > > will probably update the mouse cursor position completely independend
> > > of the refresh cycle, so the temporal resolution might be very
> > > different...
>
> > > Also, the DoEvent function is probably a leftover from the standard
> > > basic language. It is used to allow other applications to handle the
> > > message queue. I would normally not include this call in eprime
> > > experiments.
>
> > > best,
> > > Paul
>
> > > 2011/3/25 Ashtyster <ashtys... at gmail.com>:
> > > > Hi!
>
> > > > I've gotten a bit confused trying to understand how to set the
> > > > frequency of cursor position recording in E-Prime.
>
> > > > I am presenting images and recording mouse cursor positions while
> > > > subjects view the images. I would like to set the "sampling rate" for
> > > > the cursor position recording to 50 Hz. The in-line script has the
> > > > following sampling rate preset:
>
> > > > 'Give some time back (required) - i.e. sampling rate.
> > > > Sleep 20
> > > > DoEvents
>
> > > > What I am confused about is what does this '20' value mean? Does it
> > > > mean 20 cycles per second?
>
> > > > I would appreciate if somebody could answer this question.
>
> > > > All best,
> > > > Ashtyster

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