Doug,
When you say "include the derivative in the t-test" are you
implementing our approach? Or something different? Just doing a t-test on
the derivative itself (or doing a t-test on the main regressor with or
without the inclusion of the derivative) is not what I'm referring to and
will not remove delay effects.
Regards,
Vince
> -----Original Message-----
> From: SPM (Statistical Parametric Mapping)
> [mailto:[log in to unmask]] On Behalf Of d gitelman
> Sent: Tuesday, January 23, 2007 7:54 AM
> To: [log in to unmask]
> Subject: Re: [SPM] Using temporal derivative
>
> Hi Doug;
>
> I can't answer all the issues with this questions, but I
> wanted to point out
> that sometime after SPM2 was released the basis function code
> was updated so
> that the HRF and TD were orthogonalized to eachother. This
> may have affected
> the sensitivity, although I would have expected the other
> way. In spm5 they
> are also orthogonal.
>
> Darren
>
> > -----Original Message-----
> > From: SPM (Statistical Parametric Mapping)
> > [mailto:[log in to unmask]] On Behalf Of Douglas Burman
> > Sent: Tuesday, January 23, 2007 8:49 AM
> > To: [log in to unmask]
> > Subject: Re: [SPM] Using temporal derivative
> >
> > Vince,
> >
> > I see from the NeuroImage article that you tested the
> > effectiveness of including the temporal derivative in t-tests
> > with SPM99.
> >
> > In my informal tests, including the derivative in the t-test
> > did indeed improve sensitivity using SPM99, but not for SPM2.
> > I checked this after one of the other "major players" in SPM
> > wrote to the list saying that including the derivative could
> > actually decrease the responsivity.
> >
> > I haven't seen anything posted that would explain this
> > difference in SPM99 and SPM2, but the difference in my
> > informal tests on the same dataset was marked -- sensitivity
> > improved when including the derivative in SPM99, sensitivity
> > decreased when including it in SPM2.
> >
> >
> > Doug
> >
> >
> > ==============Original message text=============== On Tue, 23
> > Jan 2007 2:09:45 am CST Vince Calhoun wrote:
> >
> > No, we compute a single image quantifying the amplitude of
> > the HRF (including both derivative and non-derivative terms)
> > a nd compute a t-test at the second level. An f-test as you
> > describe will pick up differences due to either latency,
> > amplitude or some combination. Our approach is designed to
> > measure only HRF amplitude differences while removing latency
> > bias. Sort of the complement to computing a latency image
> > using, e.g. Rik Henson's approach.
> >
> > Regards,
> >
> > Vince
> >
> >
> > _____
> >
> > From: SPM (Statistical Parametric Mapping)
> > [mailto:[log in to unmask]] On Behalf Of Cédric Lemogne
> > Sent: Tuesday, January 23, 2007 1:03 AM
> > To: [log in to unmask]
> > Subject: Re: [SPM] Using temporal derivative
> >
> >
> >
> > Dear Vince,
> >
> > Thank you for the article that I will read carefully but
> > please allow me one more question.
> >
> > If you carry the temporal derivative to the second level, I
> > presume that you perform a F-contrast including both HRF and
> > its derivative, right ?
> >
> > But what about the contrats at the first level ? For my part,
> > I aimed to perfo rm t-contrasts separately for HRF and its
> > derivative at the first level, and then include both in a
> > F-contrast at the second level. Does it sound correct to you ?
> >
> > Best regards,
> >
> > Cédric
> >
> >
> >
> >
> >
> >
> > > Message du 23/01/07 08:51
> > > De : "Vince Calhoun"
> > > A : "'Cédric Lemogne'" , [log in to unmask] Copie à :
> > > Objet : RE: [SPM] Using temporal derivative
> > >
> > >
> > Dear Cedric,
> > You might find the following paper helpful which discusses
> computing a
> > corrected amplitude estimate from the derivative and non-derivative
> > parameters for use in a subsequent second-level analysis. In
> > it we also
> > shown that, for second level analysis, the inclusion of a temporal
> > derivative in the model does little to help latency-induced
> > bias unless you
> > actually take this parameter to the second level.
> >
> > V. D. Calhoun, M. Stevens, G. D. Pearlson, and K. A. Kiehl,
> > "FMRI analysis
> > with the general linear model: Re moval of latency-induced
> > amplitude bias by
> > incorporation of hemodynamic derivative terms," NeuroImage,
> > vol. 22, pp.
> > 252-257, 2004.
> >
> > Regards,
> >
> > Vince
> >
> > >
> >
> > _____
> >
> > From: SPM (Statistical Parametric Mapping)
> > [mailto:[log in to unmask]] On
> > Behalf Of Cédric Lemogne
> > > Sent: Tuesday, January 23, 2007 12:36 AM
> > > To: [log in to unmask]
> > > Subject: Re: [SPM] Using temporal derivative
> > >
> > >
> >
> > > Hello Ged, hello Douglas,
> >
> > > Yes, I did mean variability in the latency of the HRF's onset
> >
> > > Many thanks for your responses !
> >
> > > Best regards,
> >
> > > Cédric
> > >
> > >
> > >
> > >
> > >
> >
> > > Message du 22/01/07 18:04
> > > > De : "Douglas Burman"
> > > > A : [log in to unmask]
> > > > Copie à :
> > > > Objet : Re: [SPM] Using temporal derivative
> > > >
> > > > Greetings, Ged.
> > > >
> > > > In theory, I agree with your statistical approach, and
> I've seen a
> > number
> > > > of messages that indicate this is often done. In
> > practice, I only use
> > the
> > > > HRF-convolved regressor for my analyses.
> > > >
> > > > I came to this conclusion after going through a series of
> > analyses,
> > using
> > > > t-tests and F contrasts with and without the temporal
> > derivative in both
> >
> > > > SPM99 and SPM2. (I'm only recently beginning to try SPM5,
> > so I have
> > > > nothing useful to say about it.) I'll spare you the
> > details -- although
> > I
> > > > will mention that SPM99 and SPM2 differed in the
> > independence of the HRF
> >
> > > > and TD regressors when using a t-test. (SPM99 showed
> > improved activation
> >
> > > > when including both in a contrast, whereas SPM2 gave
> substantially
> > better
> > > > results when the TD regressor was omitted.) From my empirical
> > observations
> > > > on a limited number of analyses, I concluded that using the HRF
> > regressor
> > > > only for analyses was preferable, with my tests showing
> > no improvement
> > when
> > > > using the F contrast.
> > > >
> > > > I can think of theoretical reasons why this might occur,
> > although none
> > that
> > > > would suggest this must be so. Conceptually, I think of
> > the temporal
> > > > derivative as soaking up some variability that shows
> > little consistent
> > > > relationship to the effect of interest, since this
> > variability is not a
> > > > direct effect of the experimental variable. As such, I
> > often include the
> >
> > > > derivative in the model, but don't use it for analyses.
> > > >
> > > > To summarize -- I have no problem with someone's use of
> > the F contrast
> > to
> > > > include both the HRF and TD regressors, but personally I
> > prefer to limit
> > my
> > > > analyses to the HRF.
> > > >
> > > > Doug Burman
> > > >
> > > > At 03:44 PM 1/2 2/2007 +0000, Ged Ridgway wrote:
> > > > >Hi Doug,
> > > > >
> > > > >>I don't think the temporal derivative has anything to
> > do with the peak
> >
> > > > >>latency -- only with the latency for the onset of the
> > hemodynamic
> > response.
> > > > >
> > > > >Sorry, "peak latency" was a sloppy quote of mine from
> > Cedric's original
> >
> > > > >phrase "effect of the HRF peak latency variation", I
> > think we both
> > meant
> > > > >variability in the latency of the HRF's peak/onset/curve
> > rather than
> > > > >anything to do with peak as in maximum (latency).
> > > > >
> > > > >I guess the important question is: do you agree with my stats?
> > > > >
> > > > >>>I think that a t-contrast on just
> > > > >>>the HRF-convolved regressor has a null-hypothesis which still
> > contains
> > > > >>>the TD-convolved regressor without the HRF-convolved
> > one. Since this
> > > > >>>null wouldn't make physical sense, I think a more
> > correct thing to
> > test
> > > > >>>would be an F-contrast with rows including ones over
> > both the HRF-
> > and
> > > > >>>TD-convolved regressors.
> > > > >
> > > > >Cheers,
> > > > >Ged.
> > > >
> > > > Dept. of Communication Sciences & Disorders
> > > > Northwestern University
> > > > 2240 Campus Drive
> > > > Frances Searle Building, Room 2-356
> > > > Evanston, IL 60208
> > > > phone 847-467-1549
> > > > fax 847-491-4975
> > > > email: [log in to unmask]
> > > >
> > > >
> >
> > ===========End of original message text===========
> >
> >
> >
> >
> >
> >
> >
|