Dear SPM Experts,
i have recently started to use variational bayesian first level analyses for
analysing presurgical language and motor experiments because i had the
feeling that the posterior probalities are easier to communicate and easier
to understand (especially when making inferences on how likely increased
activatity for speech or motor is in regions near to the lesions).
Generally, the bayesian analyses worked extremly well.
However i have stumpled across a strange result i do not understand when
analysing a block-design language experiment (2 blockedc onditions: simple
tones vs. auditory words presented in 2 sessions). Whatever effect size
threshold (even completerly unrealistic values like > 1000) or posterior
probality i choose the PPM shows the whole brains as exhibiting posterior
prob. of 1 (i.e. the whole brain is "activated"). SPM5 displays the
following error message when is estimate the contrasts:
spm{P} image 1 : ...computing
Warning: Returning NaN for out of range arguments
> In /opt/spm5/spm_Ncdf.m at line 80
In /opt/spm5/spm_contrasts.m at line 214
In /opt/spm5/spm_getSPM.m at line 474
In /opt/spm5/spm_results_ui.m at line 264
...written spmP_0001.img
SPM computation : ...initialising
SPM computation : ...done
SPM computation : ...done
I have tried to remove and add motion parameters, analyse only one session,
use different basis functions etc... but whatever i do the problem persits.
Inspection of the files generated by SPM5 shows that the beta and SDbeta
images look reasonable. The spmP and con_SD images however contain only NaNs..
I might add that a conventional analysis results in stastically highly
signficant voxels...
Anybody has any idea what is causing this problem?
Greetings from Salzburg,
Martin
Martin Kronbichler, M.Sc.
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Department of Psychology
Center for Neurocognitive Research
University of Salzburg
Hellbrunnerstr.34, A 5020 Salzburg, Austria
e-mail:[log in to unmask]
Tel.:+43/(0)/662/8044-5162
Fax:+43/(0)/662/8044-5126
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Department of Neurology
Center for Neurocognitive Research Christian-Doppler Clinic,
Paracelsus Private Medical University
Ignaz Harrerstr.79, A 5020 Salzburg, Austria
e-mail:[log in to unmask]
Tel.:+43/(0)/662/4483-3966
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