[Mne_analysis] The default SSP operator?

[Matti Hamalainen]

Hi Tren,

On Mar 26, 2008, at 12:25 AM, Tsung-Ren Huang wrote:

> We're currently analyzing ongoing spontaneous MEG data.
> According to the MNE manual, the recommended SSP operator
> is constructed from the empty room measure.
>
> However, before we load in that empty-room SSP onto the task data,
> mne_browse_raw seems to apply a default SSP already becuase the raw
> data appear very different when we switch off the (default) SSP.
>
> It's not clear to us how this default SSP is computed
> and if this default SSP should also be turned off before the
> judge of bad channels for the task raw data.
>
> Any hints or information on this will be highly appreciated!

You really do not need to construct the empty-room SSP vectors  
yourself. The default SSP included in all data files is just this and  
usually quite effective. It only affects the magnetometer channels.  
In our environment, no empty room SSP is needed for the gradiometers.

The default SSP should be turned off for judging the bad channels.

- Matti