synchronize event markers with refresh rate

[Hank Jedema]

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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