[Eeglablist] Segment continuous EEG data into epochs based on triggers

[Arnaud Delorme]

Hi Stephen and Yadwinder,

Yes, in EEGLAB you can create discontinuous data segments, but you cannot create epochs of varying length (although see next paragraph below). The reason is that, when performing ERP or ERSP analysis, you would be averaging over different number of trials, possibly adding noise at the lower and upper time limits where there might be few trials (so what you really want to look at is the region where all data epochs are included - and in this case, you might as well create epochs of the same length). The other reason is that we wanted people to easily manipulate the EEG raw data from the command line. Data epochs of the same length may be stored in a single Matlab matrix, but epochs of different length cannot (and in fact they are stored in a cell array of matrices in Fieldtrip). 

But, according to your original message, Yadwinder, I am not sure your epochs have different lengths. For instance, if the number of sample between 'S100' and 'S102' and between 'S101' and 'S103’ is constant, you may simply extract epochs of a given length time locked to ‘S100’ and ‘S101’. If the number of samples between these pairs of event is not constant, you can in EEGLAB have concatenated epochs of different lengths. There is no menu to extract such epochs, so you might have to write a script. Basically, you would want to remove portions of data between selected event types.

Best wishes,

Arno

> On Jun 14, 2018, at 6:18 PM, Stephen Politzer-Ahles <politzerahless at gmail.com> wrote:
> 
> I'm not sure it's possible in EEGLAB to make epochs with varying durations. It is possible in FieldTrip, though.
> 
> 
> ---
> Stephen Politzer-Ahles
> The Hong Kong Polytechnic University
> Department of Chinese and Bilingual Studies
> http://www.mypolyuweb.hk/~sjpolit/
> 
> On Thu, Jun 14, 2018 at 4:10 PM, yadwinder kaur <yadwinder.k2 at gmail.com> wrote:
> Dear EEGLAB users
> 
> I have continuous EEG data with  triggers labeled as ''S100','S101,'S102','S103'. I want to segment the data into different epochs so that startepoch : 'S100' to endepoch 'S102' and another one as startepoch 'S101' to endepoch 'S103' and generate a total of 72 epochs. and at the end, I want to concatenate these trials: every epoch (S100 to S102) and (S101 to S103). I would appreciate any help here.
> 
> Thanks
> 
> Regards
> Yadwinder
> 
> 
> 
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