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Dear Vladimir and Martin, First of all, thank you very much for your responses. I undertood the onset parameter, and I was determining it correctly, but about the duration, I have a 300ms sound, do you think that I need to change the defaut value? Sorry to bother you, but I don't know how to create this more complicated input waveform. Thanks! Best, Laura 2013/7/23 Martin Dietz <[log in to unmask]> > Hi Laura & Vladimir, > > I'm very sorry for my incorrect answer - it is of course the onset of > thalamic input to the cortex and not the onset of the evoked cortical > responses itself. This is why the default of 60 ms is a reasonable > assumption for auditory evoked responses, such as the N100 starting > slightly later around 100 ms. If you assume earlier activity such as P50, > then the input parameter should reflect this. > > Best wishes > Martin > > > > On 23 Jul2013, at 4:28 PM, Vladimir Litvak wrote: > > Dear Laura and Martin, > > Martin's answer is not quite correct (although close). Onset is the time > of the thalamic input to the cortex so it should slightly precede the first > cortical peak of the ERP. For auditory paradigms the default value is > probably OK. sd is the input width (input is parametrized as a Gaussian > volley). If your input is a brief tone then again, keep the default. If you > have a something longer it might make sense to adjust your input parameters > to better match the time course of the input. It is also possible to > generate a more complicated input waveform by combining several Gaussians > with possibly different widths (just specify several onsets and sd's). > > Best, > > Vladimir > > > On Tue, Jul 23, 2013 at 12:32 PM, Martin Dietz <[log in to unmask]> wrote: > >> Dear Laura, >> >> The onset (ms) and duration (sd) parameters are used to specify the >> prior mean and standard deviation of the onset of the the first evoked >> response (ERP) in your dataset. In your case, this would be around 50 ms >> (P50) or 100 ms (N100). >> >> I hope this helps! >> >> Best wishes >> Martin >> >> >> >> On 23 Jul2013, at 11:31 AM, Laura Sánchez wrote: >> >> Dear experts, >> >> I'm new working with DCM, and I have a doubt about what does the setting >> ‘duration (ds)’ in the ‘electromagnetic model’ section mean? I was looking >> for that in the manual and other documents but I could not find a >> description nowhere. >> I'm analyzing EEG data from an auditory paradigm, and we are expecting to >> see ERP responses around 100ms. Then I don't know if the duration parameter >> refers to the duration of the sound, which is our input, or the duration of >> the response, or neither of them. >> >> Thanks in advance. Bests, >> >> >> Laura >> >> >> > >