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Dear Urs, On 9 May 2011, at 14:23, Urs Bachofner wrote: > Dear Mr. Litvak, > > I am a neuropsychology student and I'm currently working on my final > work at the University of Zurich. > I am trying to virtually analyze auditory evoked potentials in study > participants of various ages. > > I am very fond of your research article "EEG and MEG Data Analysis > in SPM8" which helped me a lot and made me understand the source > reconstruction in SPM8 a lot better. > Still there are certain questions that I cannot figure out and any > help or suggestions from your side would be greatly appreciated. I'm > sure you could easily help me a lot getting rid of the final problems. > > So if you could take the time to help me with the following > questions I would really appreciate it: > > > > 1. First off, if I want to use the Artefact Detection SPM8 offers, I > cannot figure out which one of the four possibilities would be best > for my data. As mentioned above, I want to analyze auditory evoked > potentials and my data is epoched (-100 500 ms) and I have 250+ > trials in each set of data. The sample rate is 1000. > Also, if I choose "Peak to Peak Amplitude" I can assign a certain > Threshold. Still, I cannot find any information about this > Threshold, what exactly it is and how big it should be. Since SPM does not enforce particular units on the data the threshold value depends on the typical values of your data and artefacts. You can open the data in the reviewing tool and look at a few trials and channels to figure out what the typical range of your data is. Then you can adjust the value so that not too much and not too little is rejected. > > 2. After I run the inverse solution, I get the choice between > "Evoked", "Induced" and "Trials". Intuitively I would go for > "Evoked". From your paper I understand that "evoked" applies the > settings made to each and every trial and then averages the results, > whereas "induced" averages the trials and then applies the settings > made. It's actually the opposite. > I am clearly undecided what would be better for my data. > > That depends on what you are looking for. If you are looking for evoked activity, i.e. activity which is phase-locked to the stimulus and you want to do a source analysis of ERP/ERF then you should choose the 'evoked' option. If you are interested also in activity that is not phase-locked the things that one-usually looks at with time- frequency analysis then you should use the 'induced' option. Best, Vladimir > > Thank you very much for every bit of help you can offer and thank > you for your time. > > Sincerely, > > Urs Bachofner > > > > -- > NEU: FreePhone - kostenlos mobil telefonieren und surfen! > Jetzt informieren: http://www.gmx.net/de/go/freephone