Thank you for your help. I am still confused about some details:
"MCLAREN, Donald" <[log in to unmask]> a écrit :
> This isn't a mixed effects design as you only have one group and only
> one condition. What you want to do is to use the con_001 images in a
> one-sample t-test. DO NOT USE the con_002 images in the model. I
> suspect that might have been what happened.
I am still confused about "mixed effects analysis"and random effects
analysis. In prevoius discussions from SPMlist users and the notes
from Terry Oakes page
is mentioned that "Random-Effects" analysis is also referred to as a
"Mixed Effects" analysis, since it considers both within- and
between-subject variance. Also, in SPM manual, the one-sample-t-test
is considered as a "random effects analysis".
Any comments about this?
Which test (in SPM) should I use to consider both fixed and random effects?
> Your design (SPM.xX.X)hould have a size of [7 1]; load SPM.mat and
> then use size(SPM.xX.X) to find the answer.
The "SPM.xX.X" command gives me : SPM.xX.X =
Is it right?
> A t-contrast of 1 will find the regions that are activated. A
> t-contrast of -1 will find regions that are deactivated. An F-contrast
> is simply the square of the 2 t-tests and does not have a direction.
Thank you again for your help.
> Best Regards, Donald McLaren
> D.G. McLaren, Ph.D.
> Postdoctoral Research Fellow, GRECC, Bedford VA
> Research Fellow, Department of Neurology, Massachusetts General
> Hospital and Harvard Medical School
> Office: (773) 406-2464
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> On Fri, Feb 25, 2011 at 2:33 PM, SALEM BOUSSIDA
> <[log in to unmask]> wrote:
>> Dear SPMers,
>> I have a group of 7 subjects (rats) and I would like to perform a group
>> analysis (mixed effects).
>> I have done the 1st level analysis (fixed effects) for each subject and I
>> have two con_001 and con_002 images, wich are respectively the contrast
>> image for a positive effect (activation) and for a negative effect
>> (deactivation) of one condition (current stimulation) .
>> Then, I have done a one-sample-t-test : I feed all the con_001 of each
>> subject into the 2nd level analysis , then I entered a T contrast  and
>> SPM displayed the thresholded T-statistic image. But when I entered a F
>> contrast , I have got this error:
>> ??? Inf computed by model function, fitting cannot continue.
>> Try using or tightening upper and lower bounds on coefficients.
>> Based on the procedure described in SPM8 manuel concerning the "face group
>> data", It is mentionned that I have to enter a F contrast.
>> I am confused by this and I have some questions:
>> (1) which contrast should I enter, F or T contrast? and what is the
>> differenece between them?
>> (2) Is the one-sample-t-test, the appropriate one to run mixed effects
>> (3) Do I have to run two separate "one-sample-t-test" for
>> positive(activation) and negative-deactivation) effects?
>> Thank you for your help.
>> Best regards,