Hi,
On 19 Dec 2007, at 16:47, Hallvard Røe Evensmoen wrote:
> We have unfortunately run into some more problems with our analysis
> in FSL.
> Our study gives us 3 different runs from each subject. Each run
> lasts for
> about 18 minutes, and contains 6 different modes (3 active, 2
> baseline, and
> pause). From this, we have made 16 different contrasts that should
> be more
> or less interesting.
>
> We have run all the first-level analysis without any problems.
> Higher lever
> analysis runs OK with fixed-effects, but when trying any kind of ME,
> the
> output is always corrupted; we (almost always) get this error:
>
> “ndtri domain error”
>
> Which appears in the log for the higher-level stats, almost in the
> beginning. We have searched the online FSL-forum for help regarding
> this
> error, but none of the suggestions there helped us. They suggested
> that the
> first-level analysis could be corrupted, but everything there seems
> ok. It
> also seems strange that the FE should run if data was corrupted.
>
> To further investigate the problem, we have also tried to analyze the
> lowest possible amount of data, which is one run from 2 different
> subjects,
> and only one condition (Vanlig-Strek). Still, we get the same error
> (ndtri
> domain error), and no output. So, we think we can exclude hardware
> as the
> source of our problems. We have tried different computers, different
> versions of Linux, and different versions of FSL (3.3 and 4.0).
> Nothing
> seems to help.
Most likely what's going on is that the ME maths is unhappy because
you have strong outliers in the data, but is doing it's best. Does the
final output look at all reasonable? Probably the best solution
(without removing the outliers that is) is to use just FLAME stage 1 -
does that run ok?
> As a final note, in frustration of all the FSL-errors, we ran the
> whole
> analysis in BrainVoyager, where it went smoothly.....
Indeed - or just running OLS in matlab probably won't complain
either ;-)
Steve.
>
>
> Anyone got any idea?
>
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Stephen M. Smith, Professor of Biomedical Engineering
Associate Director, Oxford University FMRIB Centre
FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
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