event sequence for Digital Output markers to StimTracker

Any suggestions for the sequence of events in Superlab when using Digital Output Markers to communicate timing of audio output. It does not appear that I can send Digital Output marker at the same time I am sending the sound from Superlab. Superlab wants events (sound, markers, etc) to be sequential, which mean I can either marker before or after the sound was sent. So if I send a Digital Output of 50msec duration and this event is immediately followed by my sound being sent, then this marker will be sent through Stimtracker to my recording device (Biopac ACKnowledge) appearing 50msec prior to the onset of the sound (since the marker takes 50msec presentation time, prior to the sound file being sent by Superlab). Is this how you would sequence these or am I missing something.

I’ll be very interested to hear if there’s an easier alternative way to deal with the issue you ask about (I’m facing a similar issue). One solution (albeit one that involves buying some additional equipment) is described on Biopac’s website in their note on eyeblink startle scoring.

Essentially, you split the auditory signal being sent from Superlab to the participant’s headphones so that it goes both to the headphones (delivering the 50ms burst of sound to the participant), and through a High Level Transducer amplifier into your MP150. You record the incoming auditory stimuli as a channel in your Acknowledge datastream, so that you get an exact marking of when the participant received the auditory stimuli. There’s a bit of an equipment cost for this set-up (the input signal isolation adapter is ~ $200, and the High level transducer module is ~ $500), but if you’re doing startle studies or EEG studies, the increased precision in timing is well worth it, to my mind.

If you already have StimTracker, you can use it to mark the onset of audio directly, i.e. without going through the USB port or purchasing additional equipment like an input signal isolation adapter or high level transducer module.

See this tech support note, Marking Onset of Auditory Stimuli With StimTracker.

My problem is quite similar. I would like to send an event marker to StimTracker at the beginning of each trial (no light sensor). If I create Digital Output event (pulse duration: 10 ms), would SuperLab wait 10 ms before the presentation of the next event in this trial, or would the pulse be sent simultaniously with the next event? What should be the duration of Digital Output event?

Yes, SuperLab will wait the 10 ms before presenting the next event. You only need to send the duration long enough for the EEG to detect it. Usually 1 ms will work.