If you only only interested in removing the bias due to the delay as
described in our paper, then it works pretty well for 3s (see fig 2 in the
paper). I suspect it will be better than not correcting even for a little
more delay, but haven't quantified this.
VDC
> -----Original Message-----
> From: FSL - FMRIB's Software Library
> [mailto:[log in to unmask]] On Behalf Of MCLAREN, Donald
> Sent: Tuesday, May 12, 2009 10:10 AM
> To: [log in to unmask]
> Subject: Re: [FSL] question on Calhoun's method
>
> (1) In a block design, the derivative should have less of an impact on
> the amplitude since you reach a plateau in the block;
>
> (2) The derivative is only good at estimating latency shifts of about
> +/- 2 seconds; see Henson et al (2002). "Detecting latency differences
> in event-related BOLD responses: application to words versus nonwords
> and initial versus repeated face presentations." The equation for
> latency will change based on the basis functions used (SPM99 in his
> paper is different from SPM5, not sure how this compares to the basis
> functions in FSL). Also, changes in the dispersion derivative cause
> changes in the latency and amplitude as well. These haven't been fully
> characterized though.
>
> On Tue, May 12, 2009 at 11:04 AM, Hans Tissot
> <[log in to unmask]> wrote:
> > Dear FSL list,
> > [ Sorry if you get this e-mail again, I was not sure if my
> previous e-mail
> > attempt worked. ]
> > I am trying to analyze a block design fMRI experiment. I
> want to use Vince
> > Calhoun's bias correction method for my data.
> > "Calhoun et al (2005), "fMRI analysis with the general
> linear model: removal
> > of latency-induced amplitude bias by incorporation of
> hemodynamic derivative
> > terms". NeuroImage 22 (2004), 252-257"
> > My understanding is that this approach (signed F-test)
> works well for delays
> > upto 3s (~ 1 timepoint for a 3s TR).
> > My question is: Is it safe to use this method if there are
> delays upto 6s (~
> > 2 timepoints) in my data?
> > If not, what approach should I take?
> > Thanks so much!
> > Hans.
>
>
>
> --
> Best Regards, Donald McLaren
> =====================
> D.G. McLaren
> University of Wisconsin - Madison
> Neuroscience Training Program
> Office: (608) 265-9672
> Lab: (608) 256-1901 ext 12914
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