My guess:
sign(V1).*sqrt(V1.^2+V2.^2+V3.^2) where V3 is dispersion deriv. (see eqn
13 in Calhoun's paper).
On 03/13/2012 03:27 PM, Laura Tully wrote:
> How would you adjust that for both time and dispersion derivatives?
>
> laura.
>
> On Tue, Mar 13, 2012 at 3:12 PM, Chris Watson
> <[log in to unmask]
> <mailto:[log in to unmask]>> wrote:
>
> From the email you linked to:
>
> you would
> first obtain the individual contrasts for each of the canonical and
> derivative terms from each subject (two contrast volumes per subject),
> as before. Then, instead of entering these volumes directly into a
> second level analysis, you would compute, for each subject, a single
> volume estimating the "amplitude" of the effects at each voxel =
> sign(V1).*sqrt(V1.^2+V2.^2), where V1 is the canonical effect contrast
> volume, and V2 is the temporal derivative effect contrast volume.
> These "amplitude" effects estimate the amplitude of the peak response
> irrespective of the delay at which it occurrs (within a reasonable
> range). Last you would enter these "amplitude" volumes in a simple
> second-level t-test for population inferences.
>
>
>
>
> On 03/13/2012 02:07 PM, Laura Tully wrote:
>
> Thanks Jonathan, that does help. I'm now trying to work out
> how to define the appropriate t-contrasts in order to compute
> the "amplitude" at each voxel as described by Sue Gabriele
> here (and discussed in Calhoun et al. 2004):
> https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=SPM;7fba87b3.0811
>
> I think that I need to define t-contrasts at the individual
> level for each of the three basis functions (canonical, time,
> dispersion) for all of my conditions [e.g. 1 0 0; 0 1 0; 0 0
> 1] Is that correct? The bit that I get stuck on is what to do
> next... according to Calhoun et al (2004) it looks like they
> created paired difference maps between conditions as well
> [CondA(allterms)-CondA(derivatives)] -
> [condB(allterms)-CondB(derivatives)] but I'm not quite sure
> how to do this, or how it relates to the "amplitude"
> computation that is discussed in the paper. Any light you
> could shed on this issue would be most appreciated!
>
> Laura.
>
> On Tue, Mar 13, 2012 at 12:45 PM, Jonathan Peelle
> <[log in to unmask] <mailto:[log in to unmask]>
> <mailto:[log in to unmask] <mailto:[log in to unmask]>>> wrote:
>
> Dear Laura,
>
> > could someone clarify for me what the betas produced using
> time and
> > dispersion derivatives are? Is it that the first is canonical
> only, the
> > second is canonical+time, and the third is
> canonical+time+dispersion, OR is
> > it canonical only, time only, and dispersion only?
>
> It's the latter—canonical only, time only, and dispersion
> only. When
> you estimate a model in SPM, the beta reflects the
> contribution of
> that model in your design matrix: beta_0001 is the first
> column,
> beta_0002 the second column, etc.
>
> Hope this helps!
>
> Best regards,
>
> Jonathan
>
> --
> Dr. Jonathan Peelle
> Center for Cognitive Neuroscience and
> Department of Neurology
> University of Pennsylvania
> 3 West Gates
> 3400 Spruce Street
> Philadelphia, PA 19104
> USA
> http://jonathanpeelle.net/
>
>
>
>
> --
> Laura Tully
> Social Neuroscience & Psychopathology
> Harvard University
> 840 William James Hall
> 33 Kirkland St
> Cambridge, MA 02138
> [log in to unmask] <mailto:[log in to unmask]>
> <mailto:[log in to unmask] <mailto:[log in to unmask]>>
>
>
>
>
>
> --
> Laura Tully
> Social Neuroscience & Psychopathology
> Harvard University
> 840 William James Hall
> 33 Kirkland St
> Cambridge, MA 02138
> [log in to unmask] <mailto:[log in to unmask]>
>
>
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