[log in to unmask][log in to unmask]> wrote:
>> Hi Donald,
>> Thanks for your response. When you say "you don't want
>> to filter out anything related to neural activity", I'm presuming that you
>> are referring to the deconvolved neural signal?
>> If so, that makes sense. However, X0 also contains user-specified nuisance
>> covariates. I would have thought it would make sense to remove those,
>> depending on what they were (e.g., movement parameters)? I guess they can
>> always be entered into the PPI regression model...
>> On 05/05/2011 11:57, "MCLAREN, Donald" <[log in to unmask]> wrote:
>>> I could be wrong, Karl or Darren please correct me if I am.
>>> X0 is composed of the high-pass filter and constant term. Thus, you
>>> want to filter these out of the Yc regressor. However, you don't want
>>> to filter out anything related to neural activity, so you wouldn't
>>> want to filter your signal and then predict the neural activity from
>>> the filtered signal, especially filtering frequencies.
>>> Best Regards, Donald McLaren
>>> D.G. McLaren, Ph.D.
>>> Postdoctoral Research Fellow, GRECC, Bedford VA
>>> Research Fellow, Department of Neurology, Massachusetts General
>>> Hospital and Harvard Medical School
>>> Office: (773) 406-2464
>>> This e-mail contains CONFIDENTIAL INFORMATION which may contain
>>> PROTECTED HEALTHCARE INFORMATION and may also be LEGALLY PRIVILEGED
>>> and which is intended only for the use of the individual or entity
>>> named above. If the reader of the e-mail is not the intended recipient
>>> or the employee or agent responsible for delivering it to the intended
>>> recipient, you are hereby notified that you are in possession of
>>> confidential and privileged information. Any unauthorized use,
>>> disclosure, copying or the taking of any action in reliance on the
>>> contents of this information is strictly prohibited and may be
>>> unlawful. If you have received this e-mail unintentionally, please
>>> immediately notify the sender via telephone at (773) 406-2464 or
>>> On Sat, Apr 30, 2011 at 8:03 PM, Alex Fornito <[log in to unmask]>
>>>> Hi Donald,
>>>> As far as I can tell, spm_regions filters and whitens the VOI time series,
>>>> and adjusts for the null space of the contrast if an adjustment is
>>>> in xY.Ic. It defines the confound matrix, X0, but does not correct for it.
>>>> The following line in spm_peb_ppi corrects for the confounds.
>>>> Yc = Y - X0*inv(X0'*X0)*X0'*Y;
>>>> PPI.Y = Yc(:,1);
>>>> So the above correction does seem to be doing something different to
>>>> spm_regions. I'm wondering why the uncorrected data, Y, is used when
>>>> generating the ppi interaction term, while the corrected data Yc is to be
>>>> used as a covariate of no interest in the PPI model. I would has thought
>>>> that Yc should be used to generate the ppi interaction term as well.
>>>> In my data, my X0 is a 195 x 7 matrix (I have 195 volumes per session).