[Mne_analysis] EEG channel positions

Denis-Alexander Engemann denis.engemann at gmail.com
Tue Apr 19 19:53:25 EDT 2016
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So difficult to guess. But if they have 0, 0, 0 it does not look like a
real position. Usually you don't have electrodes in the origin with
noninvasive techniques ;)
Could you share a small file or just the info with us? See
mne.io.write_info. And is this the Neuromag EEG? Any chance you can figure
out the exact montage of your EEG?

Denis

On Wed, Apr 20, 2016 at 1:12 AM Rezvan Farahi <rezvan.farahi at gmail.com>
wrote:

> Hi Denis,
> Thanks a lot. I thought so too but no, EEG071-EEG074 have locations
> [0,0,0] saved for them.
> I thought it might have something to do with the numbering jump from 60 to
> 65 but ECG and EOG channels don't have any positions either.
> Probably I'll have to use the digitization points but couldn't find a
> description of parameters inside raw.info['dig']? Are they in the same
> order as I have digitized during the acquisition? does it include fiducial
> and HPI locations too?
>
>
> Best,
> Rezvan
>
> On Tue, Apr 19, 2016 at 9:37 PM, Denis-Alexander Engemann <
> denis.engemann at gmail.com> wrote:
>
>> Hi Rezvan,
>>
>> can you figure out what these channels are. My suspicion would be that
>> some channels are labeled EEG but are in fact EMG, or ECG or some other
>> physiology readout. These often have no channel positions, hence 0. If this
>> is the case your solution would be to exclude those channels.
>>
>> Denis
>>
>>
>> On Tue, Apr 19, 2016 at 9:24 PM Rezvan Farahi <rezvan.farahi at gmail.com>
>> wrote:
>>
>>> Hello,
>>> I'm trying to interpolate the bad channels but it throws the following
>>> error since chs['loc'][:3] for a few channels is [0,0,0]:
>>> ValueError: 'Could not extract channel positions for 4 channels'
>>>
>>> I was wondering what could be the reason for this?
>>>
>>> And whether or not it would make sense to use positions from raw.info['dig']
>>> (since I have measured all the EEG channel positions when digitizing)
>>> together with set_channel_positions to set the missing positions?
>>> If so, where can I get more info about the structures inside raw.info['dig']
>>> to make sure which points correspond to the EEG channels
>>> (e.g. don't know what does "kind" value mean there.)
>>>
>>>
>>> Many thanks,
>>> Rezvan
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