Subject: Re: Solutions for sending triggers in an AEP (EEG) experiment? (UNCLASSIFIED) From: "Hairston, W. Dave (Cont, ARL/HRED)" <dave.hairston@xxxxxxxx> Date: Fri, 5 Sep 2008 13:13:43 -0400 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>This is a multi-part message in MIME format. ------=_NextPart_000_0349_01C90F59.38FD9A60 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Classification: UNCLASSIFIED=20 Caveats: NONE This is almost exactly how I am setting up a lab right now. We will have a line from the soundcard (and pre-amp) going into a = digital filter (likely an oscilloscope) and converting to TTL, which will go = into the interface box. Meanwhile, also send a data code via parallel port to designate the trial type. They will not arrive together, but (a) it give = you both things in the trial, and (b) also tells the delay related to Windows/Soundcard. One additional option (also considering myself) is to "steal" one or = some of the data lines on that parallel port for use by the auditory trigger. The "data" sent by the parallel port is just a 5v high swing on one of = the data pins, according to the bit logic of the value sent; there are 8 involved, providing 255 possible values. In truth, you probably only = need about 4-5 of them (32 different stimulus combinations is plenty for = me!).=20 So what one could do is to get 2 DB25-to-8 BNC adapter cables (or make a = box for cheap). Imagine taking the 2 connectors and pinning them together, = so it goes DB25 to BNC - BNC to DB 25. Now take the last 3 (corresponding to = data pins 6,7,8), and don't connect them together; rather, on the side going = into the Synamps box, connect these to each of audio-to-TTL converters as you mentioned. Voila, now you have the capability of several direct-feed = audio triggers and still retain parallel digital coding. Dave ------------------------------- Dr. W. David Hairston Research Fellow Oak Ridge Affiliated Universities Auditory Research Team, VAP, HRED Army Research Lab Aberdeen Proving Ground, MD 21005 Office: (410) 278-5925 Fax: (410) 278-3587 -----Original Message----- From: AUDITORY - Research in Auditory Perception [mailto:AUDITORY@xxxxxxxx On Behalf Of P=E1draig Kitterick Sent: Friday, September 05, 2008 11:19 AM To: AUDITORY@xxxxxxxx Subject: Re: [AUDITORY] Solutions for sending triggers in an AEP (EEG) experiment? We send an identifier code using the parallel port (whose timing is not critical) prior to the stimulus and then use a method identical to what = you describe to generate TTL triggers to accurately mark the onset of the stimulus. We can then link each trigger pulse to a stimulus type by examining the = code value that occurred immediately before the trigger. In software, the = value of the trigger pulses can then be updated to reflect the stimulus type = so that each stimulus can be identified from the trigger alone. What software are you using to analyse the EEG data? If you're using = BESA to do the analysis, you can create conditional rules to use both numerical codes in conjunction with trigger pulses to identify stimuli without = needing to post-process the data. Padraig Daniel Oberfeld wrote: > Dear list, >=20 > I would like to know whether anyone here knows a 'better' method for=20 > synchronizing acoustic stimulation and EEG recordings, more=20 > specifically, for sending triggers accurately time-locked to the audio = > signal to a multi-channel EEG system. >=20 > We use a NeuroScan SynAmps system (32 channels) for recording auditory = > evoked potentials (AEPs). >=20 > As we have a MATLAB-based stimulus generation system, we currently use = > a very simple triggering scheme. On one channel of our soundcard we=20 > create a short 10 kHz tone burst coinciding with the onset of the=20 > auditory event, and use a small circuit to convert this tone burst to=20 > a TTL pulse, which is then sent to one pin of the parallel-port-like=20 > trigger input of our EEG system. >=20 > This way we achieve submillisecond synchronicity between trigger and=20 > sound, but we have only *one single* trigger code appearing in the EEG data. >=20 > Thus, some rather complex post-processing is needed to tell the EEG=20 > analysis software which trigger event corresponded to which=20 > experimental condition... >=20 > In principle, the NeuroScan system could receive an 8-bit trigger=20 > allowing to code 256 different events. So it is tempting to use the=20 > parallel port for this. But I'm afraid it is impossible to synchronize = > the parallel port to audio under Windows XP... >=20 > Thus, my question is whether someone knows (and/or uses) a solution to = > this problem? >=20 > 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=20 > 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=20 > 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=20 > should be possible to construct such a box using some standard=20 > components like 74HC75. >=20 > So did anyone ever come across such a device, either commercially=20 > available or custom-made? > Or maybe there are also different solutions which I have not thought=20 > about yet...? >=20 > All the best, >=20 > Daniel >=20 -- P=E1draig Kitterick Graduate Student Department of Psychology University of York Heslington York YO10 5DD UK Tel: +44 (0) 1904 43 3170 Email: p.kitterick@xxxxxxxx Classification: UNCLASSIFIED=20 Caveats: NONE ------=_NextPart_000_0349_01C90F59.38FD9A60 Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="smime.p7s" MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGSIb3DQEHAQAAoIIUADCCA3Aw ggJYoAMCAQICAQUwDQYJKoZIhvcNAQEFBQAwWzELMAkGA1UEBhMCVVMxGDAWBgNVBAoTD1UuUy4g R292ZXJubWVudDEMMAoGA1UECxMDRG9EMQwwCgYDVQQLEwNQS0kxFjAUBgNVBAMTDURvRCBSb290 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