[FieldTrip] functionality change of ft_prepare_sourcemodel

jan-mathijs schoffelen jan.schoffelen at donders.ru.nl
Wed Jun 15 15:51:01 CEST 2011

Dear all,

We implemented a slight change in the default behaviour of  
ft_prepare_sourcemodel. This is a fieldtrip function (often not called  
directly by you), which creates a specified source model for inverse  
reconstruction. Typically, this is a 3D regular grid, or a 2D mesh of  
the cortical sheet. The function is typically called with additional  
input arguments, specifying geometric objects, such as a volume  
conductor model of the head, or a description of the sensor-array.

To make a long story short, before you had the option to specify  
cfg.sourceunits and cfg.mriunits.
Cfg.sourceunits refers to the metrical unit of the dipole positions,  
and this defaulted (if you didn't explicitly specify it) to 'cm'. As  
of yet, it will default to the metrical units in the input data, i.e.  
the units of the sensor-array (if provided), or the units of the  
volume conductor of the head. For example, for neuromag and 4d- 
neuroimaging users the default will now be a grid with 'm' as a unit.
Cfg.mriunits is as of now deprecated, and was used to specify the  
units of the (optional) input anatomical or segmented mri. Nowadays,  
these structures explicitly contain a unit, so that can be easily  
recovered from the data.
We will build in explicit checks on the units in which different  
geometric objects are defined (many of those are already in place,  
e.g. ensuring same units for volume conductor model of the head and  
sensor positions) in the near future.
For now, if you want to have explicitly the same behavior as before,  
you need to specify cfg.sourceunits to be 'cm'.

Best wishes,


Dr. J.M. (Jan-Mathijs) Schoffelen
Donders Institute for Brain, Cognition and Behaviour,
Centre for Cognitive Neuroimaging,
Radboud University Nijmegen, The Netherlands
J.Schoffelen at donders.ru.nl
Telephone: 0031-24-3614793

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