Solutions for sending triggers in an AEP (EEG) experiment?

[Daniel Oberfeld <oberfeld@xxxxxxxxxxxx>]

Dear list,

I would like to know whether anyone here knows a 'better' method for 
synchronizing acoustic stimulation and EEG recordings, more 
specifically, for sending triggers accurately time-locked to the audio 
signal to a multi-channel EEG system.

We use a NeuroScan SynAmps system (32 channels) for recording auditory 
evoked potentials (AEPs).

As we have a MATLAB-based stimulus generation system, we currently use a 
very simple triggering scheme. On one channel of our soundcard we create 
a short 10 kHz tone burst coinciding with the onset of the auditory 
event, and use a small circuit to convert this tone burst to a TTL 
pulse, which is then sent to one pin of the parallel-port-like trigger 
input of our EEG system.

This way we achieve submillisecond synchronicity between trigger and 
sound, but we have only *one single* trigger code appearing in the EEG data.

Thus, some rather complex post-processing is needed to tell the EEG 
analysis software which trigger event corresponded to which experimental 
condition...

In principle, the NeuroScan system could receive an 8-bit trigger 
allowing to code 256 different events. So it is tempting to use the 
parallel port for this. But I'm afraid it is impossible to synchronize 
the parallel port to audio under Windows XP...

Thus, my question is whether someone knows (and/or uses) a solution to 
this problem?

One way to do this would be via a "latched" type of "trigger box":
1) From Matlab, the parallel port is set to a specific code prior to 
sound generation (i.e., before the trial starts)
2) The trigger box sits between the parport and the EEG system
3) The trigger code is routed to the EEG system only when an audio 
trigger (like the one we use currently) is received by the "trigger box".
This would allow sending time-locked 8-bit trigger events. And it should 
be possible to construct such a box using some standard components like 
74HC75.

So did anyone ever come across such a device, either commercially 
available or custom-made?
Or maybe there are also different solutions which I have not thought 
about yet...?

All the best,

Daniel

--
Dr. Daniel Oberfeld-Twistel
Johannes Gutenberg - Universitaet Mainz
Department of Psychology
Experimental Psychology

Staudingerweg 9
55128 Mainz
Germany

Phone ++49 (0) 6131 39 22423
Fax   ++49 (0) 6131 39 22480
http://www.staff.uni-mainz.de/oberfeld/