[Eeglablist] Using EEG.epoch(x).eventurevent & EEG.urevent(x).latency to get timepoint in original data of an epoch start

[Makoto Miyakoshi]

Dear Luis,

> However, when I use this, the resulting time is NOT a
multiple of my temporal resolution

What values did you get instead? They may tell us what's wrong.

Makoto

2012/9/12 Luis Piloto <lpiloto at princeton.edu>:
> Hello everyone,
>
> I'll try to be as brief as possible and I'd like to thank you in advance
> for the help.
>
> I have 3 datasets:
>
> dataset_a.set =  EEG file containing a .CNT file that was rereferenced /
> resampled (1000 Hz --> 250Hz) and has all of the events populated, with
> EEG.data of dimensions [21, 100000] i.e. 21 channels and 10000
> timepoints BUT the EEG.times field is empty
>
> dataset_b.set = corresponds to an EEG dataset which was epoched (via
> pop_epoch()) from dataset_a for specific event(s) e.g.
> dataset_b.epoch(x).eventtype = {'31' '37'}
>
> dataset_c.MAT = matrix with dimensions [21, 100000, 50] = (# channels, #
> timepoints, #frequencies) corresponding to wavelet decomposition of
> dataset_a for 50 frequencies
>
> What I'm trying to do is utilize dataset_b to know which time points of
> dataset_a correspond to that particular epoch start to extract the
> relevant epoch data from dataset_c.  I'm currently using:
>
> time_in_dataset_a = dataset_b.urevent( dataset_b.epoch(1).eventurevent(
> 1 ) ).latency
>
> I assumed if this was working correctly, I would get something like
> time_in_dataset_a =  1.004 seconds (assuming a sampling rate of 250 Hz =
> 4 ms temporal resolution).  This would give me the 251st timepoint as
> the start of my epoch because 1.004 s * (250 timepoints per second) =
> timepoint 251.  However, when I use this, the resulting time is NOT a
> multiple of my temporal resolution and so it seems like I'm either doing
> something wrong or I've messed up my data in the epoching OR
> resampling.  Although I have looked at pop_resample.m and it does seem
> to recompute event latences as shown in the comment on top of the file
> "% 04-05-02 recompute event latencies -ad ".
>
> I look forward to hearing from you guys -- been kinda stuck on this one.
>
> Regards,
> Luis Piloto
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-- 
Makoto Miyakoshi
JSPS Postdoctral Fellow for Research Abroad
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego