Timing between digital output and picture events

Dear Cedrus community,

I am setting up an EEG experiment using SuperLab 4.03. The SuperLab is connected to a DC input of our EEG sistem, via MC PCI card, to record event markers. Event markers are DigitalOutput.

The event markers should synchronize for stimulus events–there seems to be a problem. I tied an event sequence, which was:

fixation corss - Picture event (20 ms) - Digital output (raise line) - mask event (80 ms) - Digital output (lower line)

with this sequence, I hoped to send marker signal, like:

______ (DC __ 0V, – 5V)
++++PPMMMMMMMM (+,P and M are display refresh(100Hz) for fixaton, picture and mask)

Instead I got:


There is about 50 ms delay between marker onset and lowering line. I would appreciate if you could tell me how to avoid thd delay (or a better way to send a marker to an external device).