[Mne_analysis] apply_proj question

[Dan Howarth]

Even if the signal changes between when I applied the projection and when
it is reapplied?

Let's say I compute some projections and apply them. Then I do a band pass
filter. The signal has changed and so I assume the PCA components of the
signal changes as well. So then when I reapply the projections that were
created before band pass to the band pass data I feel like they will have
an effect. But I'm an signal processing novice.

-Dan

On Tue, Nov 18, 2014 at 6:28 PM, Alexandre Gramfort <
alexandre.gramfort at telecom-paristech.fr> wrote:

> hi Dan,
>
> if a proj is applied to data, the same proj will be applied to noise cov
> and forward operator when localizing sources. Proj can be applied
> multiple times, it has no effect to reapply them a second time.
>
> HTH
> Alex
>
> On Tue, Nov 18, 2014 at 11:03 PM, Dan Howarth <d.c.howarth at gmail.com>
> wrote:
> > Hello, in the documentation for apply_proj() (see link below) it states:
> >
> >> Once the projectors have been applied, they can no longer be removed. It
> >> is usually not recommended to apply the projectors at too early stages,
> as
> >> they are applied automatically later on (e.g. when computing inverse
> >> solutions). Hint: using the copy method individual projection vectors
> can be
> >> tested without affecting the original data. With evoked data, consider
> the
> >> following example:
> >
> >
> > Does this mean that if I apply the vectors that they will then be
> reapplied
> > when I later compute the inverse?
> >
> > (
> http://martinos.org/mne/stable/generated/mne.io.RawFIFF.html#mne.io.RawFIFF.apply_proj
> )
> >
> > Thanks!
> > Dan Howarth
> >
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