StimTracker DIN latencies increase with pulse duration


I am currently configuring a StimTracker Duo (+ m-pod for EGI) for use with E-Prime and recording with Net Station Acquisition 5.4.2. To make sure I have configured the StimTracker settings correctly, I have been comparing the timing results against an EGI AV timing device. The StimTracker is currently set to single pulse mode, with visual hold-on and hold-off filters of 5 ms and a pulse duration of 5 ms. I have observed that the DINs recorded by StimTracker to visual stimuli are consistently delayed by 5 ms relative to those recorded by the EGI device despite using an identical script, equipment, and photosensor location. If I increase the pulse duration to 20 ms but leave other settings the same, the StimTracker DINs are delayed by an additional 15 ms (for both visual and auditory stimuli). Furthermore, when using single pulse mode, Net Station Acquisition appears to record all StimTracker DINs as exactly 1 ms in duration (confirmed by looking in Net Station Review and also by examining the duration values within the relevant .xml file).

All of this makes me think that (in this mode at least) Net Station is time-locking the DIN to the end, rather than the beginning, of the pulse. Furthermore, as no information is stored in the EEG file about the pulse onset or its duration, it seems that the pulse duration must be manually recorded and manually subtracted from the DIN latency to get the true stimulus onset time. Is this intended behavior? I have read much of the StimTracker documentation and cannot find anything to suggest that such a step should be necessary.

Thank you,
Dan Kleinman