synchronize event markers with refresh rate

[Hank Jedema]

Thanks to Davis, Baris, and Paul for your quick responses.
I used a writeport command in my code to send my event markers to my
recording system. I will have to look up what the exact loading time
of an image on my Elo Carroll touch screen is, because I did not
adjust for that (fixed) delay yet.
I based my question on the timing of the event markers on the
following: I collect multiple event markers for both the stimulus
appearance as well as the response timing using a electrophysiology
rig with sub-millisecond (<0.15 msec) timing accuracy. When I compare
the time difference between 2 event markers from touch screen
responses it seems that Eprime and my Plexon rig correspond nicely
(<1msec difference). When I compare the time difference between an
event marker from a stimulus appearance and a touch screen response,
there is a much greater difference (10-18msec). On a trial by trial
basis the difference between the two event markers seems to match the
stimulus.onset delay listed in the Eprime output. Based on this, I
believe that the event marker sent out by my E-prime code precedes the
appearance of the stimulus on the screen. I will try the suggestion to
use an inline as soon as the stimulus is on the screen next week. I
will also check on the thread that David provided and post my results.

Best,
Hank

On Mar 30, 2:39 am, Paul Groot <pfc.gr... at gmail.com> wrote:
> Hi Hank,
>
> The event markers should be in sync when you prepare the markers using
> the following functions:
>
> Stim.OffsetSignalEnabled = True
> Stim.OnsetSignalEnabled = True
> Stim.OffsetSignalPort = &H378
> Stim.OnsetSignalPort = &H378
> Stim.OffsetSignalData = &H00
> Stim.OnsetSignalData = &HFF  ' < this is your onset code in hexadedimal notation
>
> Where Stim is your display object.
>
> Most flatscreens have an onset delay of a few milliseconds, so this
> would be a fixed delay caused by the properties of the display.
>
> Best,
> Paul
>
> 2011/3/29 Hank Jedema <Jed... at pitt.edu>:
>
>
>
>
>
>
>
> > Hi All,
>
> > I am trying to run a stop signal response task while recording
> > electrophysiological activity on another setup. In order to get
> > synchronization of behavior with the timing of my recordings, I have E-
> > prime sent out event markers via the parallel port to an input of my
> > recording device. It seems that this works well responses, but it
> > seems that E-prime sends out the event markers for the display of
> > stimuli before the stimulus actually appears on the screen: the
> > eventmarker/timestamp is sent when the code issues the request for the
> > stimulus to appear, rather than when the stimulus actually appears on
> > the screen (i.e at the vertical blank/screen refresh after the
> > stimulus.onset delay). Is there a way to get the event marker signal
> > to synchronize with the actual appearance of the stimulus or is this
> > something that can only be corrected offline by correcting the
> > timestamps for stimulus appearance with their onset delay ?
>
> > Thanks very much for your help.
>
> > Hank
>
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