[Eeglablist] Averaging conditions in STUDY vs Command Line

[Arnaud Delorme]

Dear Nikola,

first compute your ERSP without removing the baseline. Second compute ersp1 = 10.^(ersp1log/10) and ersp2 = 10.^(ersp2log/10) for your two conditions, and take the average 10*log((ersp1+ersp2)/2). Let's continue this conversation off list as this might not be interesting to some users.

Best,

Arno

On 20 Aug 2013, at 02:33, Nikola Vukovic wrote:

> Dear Arno,
> 
> All my conditions have the same number of trials, but I'm still getting different results using the two methods. How do I move between log and absolute power space in command line?
> 
> Best,
> Nikola
> 
>> 	Arnaud Delorme	20 August 2013 07:12
>> Dear Nikola,
>> 
>> combining conditions will concatenate the trials for the 2 conditions. So if you have the same number of trials in both conditions, the result below should be equivalent. If you have different numbers of trials, the result will differ (if you use combine, the result will be the grand average of all the trials from both conditions - this will not be the case if you average two ERSP). There are also some issues of scaling. You should not average ERSP in log space, but in absolute power space.
>> 
>> Arno
>> 
>> 
>> 
>> 	Nikola Vukovic	19 August 2013 22:09
>> Dear list,
>> 
>> Until now, I assumed that selecting several conditions and combining them into one condition (using the "combine selected values" in STUDY design window) simply averages the given conditions. Once I got more comfortable with command line scripting, I started averaging them manually (by plotting the conditions separately, then averaging their ersp data output. For example ersp_avg = (ersp{1,1} + ersp{2,1})/2). However, I find that the outputs I get when manually averaging, and when averaging variables in STUDY design are completely different (compare http://cl.ly/image/0E010I0g1x21 and http://cl.ly/image/3O01242E0b0M).
>> Where does this difference come from? What exactly does the "combine selected values" function do?
>> 
>> Thank you,
>> Nikola

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