(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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