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