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Subject:

Reference for "New Segment" toolbox option

From:

>>>>> wrote:
>>>>>> Hi all,
>>>>>> I have a question concerning the code used to implement a PPI analysis.
>>>>>>
>>>>>> In the spm_peb_ppi.m function packaged with SPM8, lines 329-332 remove
>>>>>> confounds from the input seed region¹s time course:
>>>>>>
>>>>>> % Remove confounds and save Y in ouput structure
>>>>>> %------------------------------------------------------------------------
>>>>>> --
>>>>>> Yc    = Y - X0*inv(X0'*X0)*X0'*Y;
>>>>>> PPI.Y = Yc(:,1);
>>>>>>
>>>>>> PPI.Y is then to be used as a covariate of no interest when building the
>>>>>> PPI
>>>>>> regression model. However, on line 488, it is the uncorrected seed time
>>>>>> course, Y, that is input to the deconvolution routine and used to
>>>>>> generate
>>>>>> the ppi term:
>>>>>>
>>>>>>   C  = spm_PEB(Y,P);
>>>>>>     xn = xb*C{2}.E(1:N);
>>>>>>     xn = spm_detrend(xn);
>>>>>>
>>>>>>   % Setup psychological variable from inputs and contast weights
>>>>>>   %----------------------------------------------------------------------
>>>>>>   PSY = zeros(N*NT,1);
>>>>>>   for i = 1:size(U.u,2)
>>>>>>       PSY = PSY + full(U.u(:,i)*U.w(:,i));
>>>>>>   end
>>>>>>   % PSY = spm_detrend(PSY);  <- removed centering of psych variable
>>>>>>   % prior to multiplication with xn. Based on discussion with Karl
>>>>>>   % and Donald McLaren.
>>>>>>
>>>>>>  % Multiply psychological variable by neural signal
>>>>>>
>>>>>>  %---------------------------------\$Õ{-

Date:

Sat, 7 May 2011 15:19:13 +0200

Content-Type:

text/plain

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 text/plain (12 lines)
 ```Dear SPM list, I am looking for a reference/description for the 'New Segment' method as implemented in an SPM8 toolbox. I understand (from the SPM8 manual) that it is an extension of the unified segmentation / normalization algorithm introduced in SPM5, but is the 2005 NeuroImage paper, "Unified segmentation", still appropriate, or is there a paper other than the chapter 25 in the handbook? Thank you in advance Roberto Viviani ```