Hi Freesurfer experts

I am making an analysis in Freesurfer version 6 and I have a question about the "refeventdur" in mkanalysis-sess command.

My stimulus duration is 16 seconds, but for a specific analysis, I only want to include half of the stimulus duration (ex: the first 8 seconds only OR the last 8 seconds only).

I was wondering if I can do this, by setting the "refeventdur" to 8 seconds.  Will that work? and if it does, is it including the first 8 seconds or the last 8 seconds?

Thanks

Mona