Hello, we’re using c-Pod to send event markers to BIOPAC STP100C during ERP recordings. The purpose of the event markers is to record the moment when a visual stimulus is presented. Is there any way to determine the time delay between when the event marker appears and when the visual stimulus appears on the screen? As I understand it, photocells cannot be used with c-pod. Is there any other way to calculate the time delay?
Thanks, Mark Schmidt
I cannot think of a general purpose way to determine the time delay between when an event marker appears and when the visual stimulus appears. This would require equipment like StimTracker and the delay value would depend on the computer hardware, especially the refresh rate.
There was some major retooling done in SuperLab version 6.3; see this blog post. We added the ability to have SuperLab generate event markers automatically:
With this feature, we still don’t know what the delay is but we know it is fairly fixed. The drawback of this method is that event markers are produced for any and all pictures. A workaround would be to create a Digital Output event to indicate the type of picture, e.g. stimulus or cue.
If you want to go the light sensor route and want to avoid the cost of StimTracker, the most cost effective way of doing so is a combination of Riponda and an m-pod. See this m-pod for Biopac page.