[Eeglablist] Time-Freq Decomp. and Pop_epoch - avoid edge artifacts

[Arnaud Delorme]

Dear Luis,

there will be no edge effect when using newtimef. The edge effect that you are mentioning is when you filter your data. We performing time-frequency decompositions, you are safe. However, you will miss some data at the edges of your epochs. This is why we recommend to extract large data epochs to perform time-frequency decompositions.

If your data epoch is from -1000 ms to 2000 ms (see note). Newtimef will apply a sliding window of say 500 ms wide. It means that the center of the first window will be at -750 ms and the center of the last window 1750 ms. These will be the limits of the time-frequency transform.

Hope this helps,

Arno

Note: in reality, if you have 3-second epochs, the limits will be -1000 ms to 1996 ms for example at 250 Hz and not from -1000 ms to 2000 ms. This is because, by convention, we use the beginning of a time window for each data sample. -1000 ms represents time from -1000 ms to -996 ms. -996 represents time from -996 to -992 ms. Similarly 1996 ms represents data from 1996 ms to 2000 ms. So we really have 3 seconds of data but the limits are -1000 ms to 1996 ms.

On Jul 10, 2012, at 2:05 PM, Luis R. Piloto wrote:

> Hello,
> 
> I was wondering how I can perform time-frequency decomposition on my entire dataset and *then* split the resulting data into different epoch types based on port codes.  I know how to do each of these steps individually i.e. time-freq. decomp with newtimef() and splitting the data with pop_epoch(), but I have no clue how to use the output of newtimef with pop_epoch.  I'd like to split the data AFTER performing the time-frequency decomposition because the literature says that you get edge-artifacts from time-freq decomposition and performing it on the entire segment is obviously preferable to introducing edge-artifacts to each split segment.  Thanks in advance.
> 
> Regards,
> Luis Piloto
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