Can I get a finer measurement of session start time?

[jarvis24]

You can get precision synch data for this kind of thing by way of sending out a TTL signal. Can you ask your techs if the external hardware is capable of receiving an incoming TTL signal via the parallel port? If so, it's great because you can then send a signal from DirectRT at the onset of any stimulus--in virtually perfect synch. You could do this just on the first trial, or on every trial. A quick search on the boards here for TTL ought to turn up additional info. You can also see the user's guide for the section on TTL signals an synching with other programs and/or external hardware (e.g., for psychophysiological measures).

[balford@work]

We've run our pilot study, and I'm trying to calculate the time elapsed since the start of the experiment so we can synch the events during the experiment with biometric data we measured for each subject. I'm accumulating the log's "Started@" values for each trial to add to the initial "Time" value, because I thought that would yield the time that a trial began. However, these calculated trial-start times don't match up with the biometric data times.

I used block=0 for instructions at the beginning and in between groups of trials. Previously I thought that the Started@ values for the block-not-equal-to-zero trials accounted for the block=0 times, i.e., that the Started@ value for a trial after a block=0 trial included the time taken up by the previous block=0 trials. Now I'm wondering whether I'm basically screwed, i.e., that I need to know those block=0 times to be able to calculate the time since start of the experiment.

So, please confirm: can I calculate the time since experiment start without specific time information for the block=0 trials?