Hi Diane,
There two things you need to be aware of:
1) SPM computes mean power which a non-negative quantity. I don't know
how you define 'activity' but it can also be defined to have a sign.
2) When exporting to images the power is normalized to reduce
inter-subject variance. So although the locations of activations will
not change you need to be careful when interpreting the values you get
from those images. In the present implementation the data is also
normalized prior to the inversion so there is no way to get output in
physically meaningful units even if you remove the normalization of
images.
Vladimir
On Tue, Sep 21, 2010 at 1:25 PM, Diane Whitmer <[log in to unmask]> wrote:
> Hi Vladimir,
> Thank you for your reply.
>
> Just to make 100% sure I understand you correctly:
> If I generate a contrast of, e.g. 8-12 Hz and the full time window of my
> trial (8.5 seconds), and then click on Image, the red colored activation
> region represent the mean activity of each voxel over my selected time and
> frequency windows?
>
> -Diane
>
>
> On Tue, Sep 7, 2010 at 8:16 PM, Vladimir Litvak <[log in to unmask]>
> wrote:
>>
>> Dear Diane,
>>
>> Averaging over time is done when you compute a contrast. Just
>> contrasts looks at the power rather than raw J. If you want something
>> different you can write your own code or modify spm_eeg_inv_results.
>>
>> Best,
>>
>> Vladimir
>>
>> On Wed, Sep 1, 2010 at 11:12 AM, Diane Whitmer <[log in to unmask]>
>> wrote:
>> > Dear SPMers,
>> >
>> > Does anyone know how to plot features other than the maximal intensity
>> > projection from the M/EEG inverse solution?
>> > For example, which function should I modify in order to create an image
>> > from
>> > J averaged across time samples within a trial (rather than the max J in
>> > a
>> > given trial)?
>> >
>> > Thank you,
>> > Diane
>> >
>
>
>
> --
> Diane Whitmer
> Researcher in Applied Neuroscience
>
> C. Teodor Roviralta, 45
> 08022 - Barcelona - Spain
> tel. +34 93 254 03 70 x26
> fax. +34 93 212 64 45
> email. [log in to unmask]
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