weird result for EEG visual N1 source localization using lcmv

[Chen]

Hi,

I am doing source localization on EEG biosemi 128 channels recordings and 
get weird result. I am giving the details in the following to seek any 
help:

KrisS = eeglab2fieldtrip(EEG,'preprocessing');
cfg=[];
cfg.latency=[.08 .12]; %latency of N1
cfg.covariancewindow=[.08 .12];
cfg.covariance='yes';
cfg.keeptrials='no';
datTest=timelockanalysis(cfg,KrisS);
clear KrisS
cfg = [];
cfg.showlabels = 'yes'; 
cfg.fontsize = 5; 
figure(1);topoplotER(cfg,datTest);

datTest.elec.pnt = 1000 * datTest.elec.pnt*[0 -1 0; 1 0 0;0 0 1]; %convert 
electrode coordinates from m to mm and make the x go to nose

load standard_vol.mat %use standard BEM vol from EEGLAB
load standard_mri.mat %use standard mri from EEGLAB

cfg=[];
cfg.vol=vol;
cfg.grid.xgrid='auto';
cfg.grid.ygrid='auto';
cfg.grid.zgrid='auto';
[grid] = prepare_leadfield(cfg, datTest);

cfg=[];
cfg.grid=source2sparse(grid);
cfg.method='lcmv';
cfg.vol=vol;
cfg.projectnoise='yes';
cfg.lambda=1;
[sourceN1] = sourceanalysis(cfg, datTest);

cfg=[];
cfg.powmethod='none'; %only option that works
[sourcenai] = sourcedescriptives(cfg, sourceN1);

cfg =[];
cfg.downsample = 2;
cfg.funparameter  = 'nai';%or neural activity indes (nai)
sourceN1F=source2full(sourcenai);
[interp]=sourceinterpolate(cfg,sourceN1F,mri);
figure(3);sliceinterp(cfg,interp)


I have the following specific questions:

1. Should the units all be mm?
2. Is my coordinate rotation right?
3. How to choose the value of lambda? I just randomly choose 1 now since 
without lamda I always get warnings of rank-deficient and divided by zeros.
4. Since I am using the standard BEM and mri, my electrodes are not on the 
skin( see the attached figure), when I try to realign based on fiducials, 
it is still the same. I check the function of electroderealign and find 
out that norm.m is always identy matrix which make the realign doing 
nothing. Why?

Appreciate to point out what I am wrong.

Chen
-------------- next part --------------
A non-text attachment was scrubbed...
Name: TopoN1.jpg
Type: image/pjpeg
Size: 43181 bytes
Desc: not available
URL: <http://mailman.science.ru.nl/pipermail/fieldtrip/attachments/20070320/a62a7ccf/attachment-0003.bin>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: N1source.jpg
Type: image/pjpeg
Size: 32703 bytes
Desc: not available
URL: <http://mailman.science.ru.nl/pipermail/fieldtrip/attachments/20070320/a62a7ccf/attachment-0004.bin>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: ElecHead.jpg
Type: image/pjpeg
Size: 36116 bytes
Desc: not available
URL: <http://mailman.science.ru.nl/pipermail/fieldtrip/attachments/20070320/a62a7ccf/attachment-0005.bin>