Dear Diane,

Did you modify the montage to rename the channels to 10-20? If so,
your situation is a slightly tricky one. Montage function is supposed
to assign default channel locations but it won't in your case because
there already are channel locations present. I'll change the code to
handle this unusual case, but for now you can just go to 'Prepare' and
assign default channel locations after montage.

Best,

Vladimir

On Thu, Jun 25, 2009 at 1:58 PM, Diane Whitmer<[log in to unmask]> wrote:
> Hi Vladimir,
> Regarding the montage file that you sent me, does this file just take care
> of converting to average reference, or does it also set the electrode
> positions? When I plot the channel positions via Prepare, it appears that
> SPM knows where the electrodes are located. However, when I look at the
> Channels under Review, position is set to "no" for all the channels. So, I
> am a little bit confused.
> Thanks,
> Diane
>
>
> On Tue, Jun 23, 2009 at 5:02 PM, Vladimir Litvak <[log in to unmask]>
> wrote:
>>
>> Dear Diane,
>>
>> It doesn't matter if you subtract EXG1 or not because its contribution
>> will be canceled out when you convert to average reference. I realized
>> it the hard way when trying to make a montage matrix that does both
>> the subtraction and average referencing for you so this is really the
>> mathematical truth.
>>
>> If you replace labelnew in the montage with what you sent me then
>> you'll get what you want.
>>
>> Best,
>>
>> Vladimir
>>
>> On Tue, Jun 23, 2009 at 11:42 AM, Diane Whitmer<[log in to unmask]>
>> wrote:
>> > Hi Vladimir,
>> > Thank you for the montage file. I forgot to mention to you that channel
>> > #65
>> > is the original reference, so the 64 channels should first subtract #65,
>> > and
>> > then be re-referenced to average. Otherwise, we an lose up to 40 dB of
>> > SNR,
>> > according to Biosemi.
>> >
>> > Also, the labels in the montage file remain A1-A32, B1-B32. Would it be
>> > possible to change them according to the labelnew.mat that I've attached
>> > here? I realize you probably included the correct spherical coordinates
>> > for
>> > each channel, but the interpretation with later data analysis is a
>> > little
>> > bit easier with the more intuitive 10-20 channel labels.
>> >
>> > Would you be willing to update the montage file to make these two
>> > changes
>> > and resend it? I am not sure how to do it.
>> >
>> > Thank you,
>> > Diane
>> >
>> >
>> > On Mon, Jun 22, 2009 at 6:21 PM, Vladimir Litvak
>> > <[log in to unmask]>
>> > wrote:
>> >>
>> >> Dear Diane,
>> >>
>> >> I sent you via yousendit an updated version of SPM with support for
>> >> biosemi64. This will be in the next public release so once it comes
>> >> out you can keep updating. I won't get into supporting other biosemi
>> >> variants for now as I don't have data examples for them. With this
>> >> version you don't need to do 'prepare' and everything will be done
>> >> automatically. You should just do montage. For that you can use the
>> >> attached montage file.
>> >>
>> >> Let me know if you still have problems.
>> >>
>> >> Best,
>> >>
>> >> Vladimir
>> >>
>> >>
>> >> On Mon, Jun 22, 2009 at 4:24 PM, Diane
>> >> Whitmer<[log in to unmask]>
>> >> wrote:
>> >> > Dear Vladimir,
>> >> >
>> >> > On Mon, Jun 22, 2009 at 12:54 PM, Vladimir Litvak
>> >> > <[log in to unmask]> wrote:
>> >> >>
>> >> >> Dear Diane,
>> >> >>
>> >> >> Things are becoming clearer and I think we are quite close to
>> >> >> resolving your problems.
>> >> >>
>> >> >> > We have a 64-channel standard Biosemi system. From what I
>> >> >> > understand,
>> >> >> > you
>> >> >> > can order Biosemi with 32, 64, 128, or 256 channels. Can SPM work
>> >> >> > with
>> >> >> > 64
>> >> >> > channels if they have standard 10-20 names?
>> >> >>
>> >> >> We haven't seen a Biosemi system with less than 128 channels but
>> >> >> since
>> >> >> you have one, it should be supported. The question is, is the EEG
>> >> >> cap
>> >> >> you are using a standard one for 64-channel Biosemi or is it
>> >> >> something
>> >> >> you ordered separately and other labs with 64-channel Biosemi
>> >> >> systems
>> >> >> are likely to have other caps? Also is the mapping between Biosemi
>> >> >> and
>> >> >> 10-20 labels that you are using just something approximate or do you
>> >> >> have some documentation from Biosemi saying that this is the right
>> >> >> correspondence?
>> >> >
>> >> > Further information on the Biosemi electrode caps can be found here:
>> >> > http://www.biosemi.com/headcap.htm
>> >> > As you can see, they have a variety of sizes. For 64, 32, or 16
>> >> > electrodes,
>> >> > they map to the 10-20 system. Attached is the file that is
>> >> > downloadable
>> >> > from
>> >> > the Biosemi website with spherical coordinates for the electrode
>> >> > positions.
>> >> > We will eventually use a Polhemus system for more accurate electrode
>> >> > positions, but for now we assume that the cap is placed on the head
>> >> > as
>> >> > precisely as possible.
>> >> >
>> >> >>
>> >> >> The reason I'm asking you all this is as follows. If your system can
>> >> >> be considered a standard Biosemi 64 system, then I can add default
>> >> >> support for it in SPM. I have already added automatic recognition of
>> >> >> EEG channels and to make it complete I need a file with 3D electrode
>> >> >> positions. If you are sure that the channels correspond exactly to
>> >> >> 10-20 locations, then just send me the full label mapping you are
>> >> >> using and I'll make this file myself. If not, then perhaps you can
>> >> >> find somewhere a locations file with fiducials for your cap or you
>> >> >> can
>> >> >> make a good quality measurement in your lab with a 3D digitizer.
>> >> >
>> >> > It sounds like SPM support for 64, 32, and 16 channel systems might
>> >> > be
>> >> > useful to other end-users in addition to us.
>> >> >
>> >> >>
>> >> >> If your cap is something that is not likely to come with other
>> >> >> Biosemi-64 systems then we still can make a locations file for you,
>> >> >> just it won't be included in SPM distribution. Then you won't have
>> >> >> to
>> >> >> rename your channels with the GUI every time.
>> >> >
>> >> > Please let me know when this locations file is ready and how I should
>> >> > incorporate it into the preprocessing stream.
>> >> >
>> >> >
>> >> > Thank you again for all your help.
>> >> >
>> >> >
>> >> > Sincerely,
>> >> > Diane
>> >> >
>> >> >
>> >> >
>> >
>> >
>> >
>> > --
>> > Diane Whitmer,
>> > Researcher
>> >
>> > 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,
> Researcher
>
> 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
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