Manage the timing of markers

The forum won’t let me upload my experiment (security token missing? I got this error twice after watching it upload to 100%), but I’ll post the question anyway.

It is repeated measures with three conditions, and the crucial event that we will associate with psychophysio variables happens right in the middle of each stimuli. We need markers that occur at the onset of each (10 sec) stimulus, but then also at the 5 sec mark. I think the event onset markers I have now are set properly, and the exp works with the stimtracker (though it’s kind of hard to tell if they are exactly right). But I don’t know how to set markers for the 5 sec point during each stimulus. Do I have to create separate (i.e., second) markers for each event? And what settings would I put?

Thanks so much!

There are a couple of ways to accomplish what you want.

The first method is to use an event of type Digital Output like you have been doing. You will need three events:

  • A sound file that plays and that has the option [B]Wait for audio to finish playing[/B] turned off.
  • A digital output event that sends an event marker, say, 10 milliseconds long. This will coincide with the start of the sound file. This event should have a time limit of 4990 milliseconds (that’s 5000 minus 10).
  • Another digital output event for sending the second event marker. This event marker will go out approximately 5000 milliseconds into the sound file being played.

The second method takes advantage of StimTracker’s built-in audio marking capabilities. If your experiment does not involve dichotic listening, you can use a sound editor to do the following: have the actual sound play on one channel, and place event markers on the second channel. When playing the sound file, you want to make sure that the second channel is turned off (easily accomplished if using external speakers) so that the participant doesn’t hear noise caused by the event markers.

I highly recommend the second approach if it’s suitable for your experiment. It will take a little bit of work to edit the sound files, but this approach offers three advantages:

  • It will be accurate down to sub-milliseconds, microseconds even, with no variability.
  • It simplifies the design of your experiment in SuperLab because you will no longer need to send event markers to mark the onset of audio.
  • If you want to send event codes from SuperLab, e.g. to describe the trial being presented, you now have at least one more bit of information available.
Let me know if you have any follow up questions.

Thanks Hisham. Is there any way we can talk on the phone about this? I’m still unclear how to modify what I have already to the first option. The second option isn’t really feasible because I need the files to play in stereo with headphones.

My main issue here is that I don’t know what all the settings should be

Of course, call me at (800) 233 -7871 or (310) 548-9595, tomorrow or later, after 9:30AM California time.