[FieldTrip] unit gain for Fieldtrip's LCMV beamformer - unit

[russ port]

Hi All,

As an update to this post, which I fear may be otherwise left alone, it seems that the Wiki now states that the virtual channel with be of "the equivalent current dipole source” (http://www.fieldtriptoolbox.org/tutorial/shared/virtual_sensors <http://www.fieldtriptoolbox.org/tutorial/shared/virtual_sensors>). I assume then if its a ECD ("equivalent current dipole”) is in A(what ever the source model is in i.e. Am, or Am etc etc). Therefore you should just be converting to your units of choice (for me nAm). Does this seem correct?

Best,
Russ

> On Sep 29, 2015, at 10:54 PM, russ port <russgport at gmail.com> wrote:
> 
> Thanks Marc,
> 
> Sorry for taking so long to respond. I am quite confused now. I think I get what you are talking about with "unit gain" and "unit noise-gain” as defined by Sekihara, as much as I can make out at least with out having the book you refer to (on the bright side I now know what to nag my boss for). I suppose I was a quite mis-leading with what I had in my last email, by which, what I actually did was use the LCMV beamformer to make lead fields to calculate the virtual sensors (see http://www.fieldtriptoolbox.org/tutorial/shared/virtual_sensors <http://www.fieldtriptoolbox.org/tutorial/shared/virtual_sensors>). Of note, your link to the discussion list is now even more useful. I am using centimeters and a single shell head model. The wiki says "CMV beamformer spatial filter for the location of interest will pass the activity at that location with unit-gain”. From your email, I suspect then that the output would be in Am units. I am a little concerned though that both my output, and the field trip wiki shows values ranging ~ -3 -> 3 (e-4, i.e. mAm not nAm). Or instead would the units be in T/(Am) (if I apply the 1e4 unit conversion). Sorry for not being better at this, I think I do need those books you were mentioning...
> 
> Best,
> Russ
> 
> 
> 
> 
> 
>> On Sep 11, 2015, at 12:40 PM, Marc Lalancette <marc.lalancette at sickkids.ca <mailto:marc.lalancette at sickkids.ca>> wrote:
>> 
>> mformer with unit gain would have Am units.
> 

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