Dear Diane,
Your new montage is quite good, but you should decide what you want to
do about the 'EXG1' channel. Presently it appears in the montage, but
is actually set to zero. I understand this is your reference. I saw in
the history that you are using SPM's default channel locations. SPM
wouldn't have a location for EXG1 and wouldn't mark it as 'EEG' by
default. So you have two options:
1) If you want to use it as an extra EEG channel you need to either
change its name to some 10-20 name and assign default channel types
and default locations again or at least change its type to 'EEG' in
the 'prepare' interface and load a locations file where this channel
appears. Then you should make a montage like what you did just with 65
channels including EXG1 so
tra = eye(65) - ones(65)/65;
2) If you can live without it, you can use the montage you sent me, or
even simpler just don't include EXG1 in the montage at all. You can
either keep it in the file as a non-EEG channel or not keep it, for
source reconstruction it doesn't matter.
Once you convert the data to average reference, try the source
reconstruction again. If there is still a problem, average your data
and see if for averaged data you get the same error message. If so
send it to me, the file will be much smaller. If you only get the
error for epoched data, but not for averaged let me know and we'll
think of a way for you to send me the epoched file.
Best,
Vladimir
On Wed, Jun 17, 2009 at 11:12 AM, Diane Whitmer<[log in to unmask]> wrote:
> Vladimir,
> I tried to send the .dat file, but it was over 100MB and therefore cannot be
> sent via yousendit without a subscription. Do you have another suggestion?
> Thanks,
> Diane
>
>
> On Tue, Jun 16, 2009 at 9:38 PM, Vladimir Litvak <[log in to unmask]>
> wrote:
>>
>> Dear Diane,
>>
>> The error might have something to do with the fact that the montage
>> matrix you used is wrong. To do what you intended you'd need the
>> transpose of what you specified, but as I mentioned to be on the safe
>> side it'd be better to convert the data to average reference. In your
>> case of a 64 channel system you'd need something like:
>>
>> tra = eye(64) - ones(64)/64;
>>
>> for the EEG channels (or if you have 65, the same with 65).
>>
>> Best,
>>
>> Vladimir
>>
>> On Tue, Jun 16, 2009 at 12:37 PM, Diane Whitmer<[log in to unmask]>
>> wrote:
>> > Dear SPMers,
>> >
>> > I am using SPM8 with EEG data. When I try to compute the Inverse
>> > solution, I
>> > get the following error message:
>> >
>> > Warning: Matrix is singular, close to singular or badly
>> > scaled.
>> > Results may be inaccurate. RCOND = NaN.
>> >
>> >
>> > Does anyone have suggestions for how to debug this?
>> >
>> > A subset of these data previously worked for computing an Inverse
>> > Solution.
>> > One difference with my current dataset is that I have re-referenced to
>> > one
>> > of the EEG channels (because it's not clear that SPM selects a reference
>> > channel when importing from Biosemi). This may or may not be related to
>> > the
>> > problem I'm having.
>> >
>> >
>> > Thank you,
>> > --
>> > Diane Whitmer, Ph.D.
>> > Researcher in Applied Neuroscience
>> >
>> > C. de l' Observatori Fabra s/n
>> > 08035 - Barcelona - Spain
>> > tel. +34 93 254 03 68
>> > fax. +34 93 212 64 45
>> > skype. dwhitmer
>> > email. [log in to unmask]
>> > ______________________________________
>> > STARLAB, Living Science http://www.starlab.es
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>
>
> --
> Diane Whitmer, Ph.D.
> Researcher in Applied Neuroscience
>
> C. de l' Observatori Fabra s/n
> 08035 - Barcelona - Spain
> tel. +34 93 254 03 68
> fax. +34 93 212 64 45
> skype. dwhitmer
> email. [log in to unmask]
> ______________________________________
> STARLAB, Living Science http://www.starlab.es
>
> This e-mail and the attached files contain confidential information and are
> of exclusive use for the addressee. The disclosure, copy and distribution of
> the present message and its attachments are prohibited. If you are not the
> intended recipient and you receive this communication, we inform you that it
> is forbidden by law to read, copy or use it. Please notify us at
> [log in to unmask] and proceed immediately to delete it.
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