Iroise,
Thanks for the information. However, for the proposed analyses you will
probably need to consider some additional factors, if you haven't already.
The use of age as a covariate makes the assumption that changes in brain
development (e.g., growth and functional complexity) are linear, which will
likely need to be discussed amongst your group. For both sets of analyses,
you are likely to run into the 'spatial normalization' problem. That is,
children's brain should not be simply warped into adult brain space, they
are not directly spatially comparable. That is, the size, shape and ratio of
white/grey matter of structure X for a 6-year old should be very different
from than that of a 20-year old. Consequently, careful consideration is
needed to determine if a the covariate of age, in months, is sufficient to
explain differences in brains if any other factor aside from 'getting older'
is being investigated.
These are just my thoughts/concerns, and I don't have a ready answer to the
problem, but it's an issue that we are dealing with also (but on a 'back
burner). I'd be happy to continue to discuss this and get additional
feedback from the other users about how to deal with these types of issues.
Cheers
Jason
On 9/17/10 10:08 AM, "Iroise Dumontheil" <[log in to unmask]> wrote:
> Hi Jason,
>
> we are using this model both for VBM (Dartel) and fMRI data.
>
> With fMRI we run a Condition B - Condition A contrast from the first level
> individual subject analyses and they are the images we use in the 2nd level
> analysis.
>
> With VBM we use individual subjects' grey matter images, so I guess it means
> there is only one level of analysis.
>
> But we'd like to run the same analyses on both types of data if possible.
>
> 'Developmental level' is in the model as an age (in months) covariate. So we
> have both the testing time/round and age at testing in the model. Does this
> make sense? (and is it correct?!).
>
> Iroise
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