[FieldTrip] Time Frequency Analysis - optimal trial segment length and artifact issues

[Poppy Watson]

Dear Fieldtrippers,

I have some conceptual questions about the ideal trial segment length for eventual TFR (I'm running TFR in the 2-30Hz range).
Of course for TFR, the longer the segments are the better. Although I have long ITIs and can theoretically take 3000-4000ms segments into the TFanalysis processing pathway - I currently don't because of concerns about artifacts (particularly blinking) in these longer segments. I currently reject trials where artifacts are found within the specific 1 second range (plus an extra 250ms padding at the front) that I will eventually use for statistical analysis. I then baseline correct using the extra 250 ms (I know baseline correction is another discussion point but I have reason to do it here).I then trim the segments down to 1250ms length and use those in the TF_freqanalysis. But I know these are too short and there are issues in representing the lower frequencies on plots etc.

So my query is - what if there are eye artifacts in the longer 3 second segments?? Does this not do strange things to the power representation of certain frequencies? Of course I could widen the time interval of my artifact rejection procedure but fear that too many trials will be rejected because people do need to blink at some stage and they are told to do this in the ITI so as not to do it during the crucial 1 second window (another concern is that within 200 ms of this critical analysis window participants start moving their eyes meaning that eye movements artifacts would definitely appear in any after-padding). Or - does it not matter if there are occasional artifacts in this 'padded' area that will not end up in statistical analysis? What do others do in these situations?

Much appreciated
P.Watson

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.science.ru.nl/pipermail/fieldtrip/attachments/20190515/34f38e4f/attachment-0001.html>
-------------- next part --------------
_______________________________________________
fieldtrip mailing list
https://mailman.science.ru.nl/mailman/listinfo/fieldtrip
https://doi.org/10.1371/journal.pcbi.1002202