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Dear Panagiotis, It's hard for me to see how this can happen because event times are not modified by downsampling, but if you have an example where this can be reproduced I'd like to look at it. Best, Vladimir On Mon, Jun 20, 2011 at 10:56 AM, Panagiotis Tsiatsis <[log in to unmask]> wrote: > Hi Jing, > > Just a thought... > > Did you downsample a continuous file before epoching? I have noticed that if > I downsample a continuous (CTF-MEG) file after filtering and before > epoching, the triggers shift in a weird way (up to +/-10ms) even if he > downsampling rate is very close to the original one... (I mean, you expect a > reasonable jitter in the triggers if you go from 1000Hz to 200Hz, but not > +/-10ms if you go from 1000Hz to 950Hz for example). I wanted to > investigate this issue further and provide a proper report but I did not > have the time to do it yet... and maybe I got something else wrong. > > Anywayz, > Good Luck :) > > > > On 6/20/2011 11:45 AM, Jing Kan wrote: >> >> Dear SPMers, >> >> Thanks for your concern! >> >> I am dealing with the MEG data pre-processing. After the steps of filter, >> epoch, artifact detect, averaging and baseline checking, I realized the >> response shifted a few seconds, i.e. the strong response occurred after >> the stimulus shifted into 7 ms before the stimulus. >> >> May I ask is anyone know the reason about this? >> >> Many thanks in advance! >> >> Jing > > > -- > Panagiotis S. Tsiatsis > Max Planck Institute for Biogical Cybernetics > Cognitive NeuroImaging Group > Tuebingen, Germany >