> Why don't you want to get ts with variance related somehow to your task(s) and regress out effects of no interest?
Yes I agree - it does seem odd to want to regress out task-related variance
Steve
On 27 Aug 2011, at 20:32, Dr I.J. Bohr wrote:
> There are a couple of points remaining here:
>
> 1. weights for F-contrast (unlike T-contrast) are defined as a matrix with as many rows as effects of interest (eof): ones attributed (you compare everything with everything else in both direction, so all significant variance related to these regressors is extracted.
>
> 2. what is the point of defining constant term as your eof, it's just a scalar: mean signal for the whole session, so there is no variance there at all?
>
> Why don't you want to get ts with variance related somehow to your task(s) and regress out effects of no interest?
>
> Iwo
>
> On Aug 27 2011, Steve Fleming wrote:
>
>> Hi Peter,
>>
>> Yes I think for your purposes it would be the latter (zeros(1:11) 1).
>> As Iwo pointed out, the "adjust data" option removes the null space of your F-contrast, i.e. the zeros, from your timeseries. See lines 143-153 in spm_regions.
>>
>> Hope that helps
>>
>> Steve
>>
>> On 27 Aug 2011, at 19:11, Peter Michalsky wrote:
>>
>>> Hello Iwo,
>>> first let me thank you for your reply. You understood correctly that I want to regress out all nuissance factors while extracting a time-series from a VOI. However, I also want to regress out the task variance (first two regressors in the design matrix). Hence, I want to regress out all 11 regressors and only keep the mean time-series. Do I do that by ones(1:11) zeros(12) or by zeros(1:11) ones(12). If I understood you correctly the correct solution should be to define an F-contrast with all zeros except for the constant (zeros(1:11) 1). Maybe you could explain to me why the opposite (ones(1:11) 0), which I thought would be right is wrong. Thanks again for your help.
>>> Peter
>>
>> ____________________________________
>> Stephen M. Fleming PhD
>> Wellcome Trust Postdoctoral Fellow
>> http://web.me.com/stephen_fleming/web/Welcome.html
>>
____________________________________
Stephen M. Fleming PhD
Wellcome Trust Postdoctoral Fellow
http://web.me.com/stephen_fleming/web/Welcome.html
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