# edge effects in computation of induced power?

**URL:** <https://mne.discourse.group/t/edge-effects-in-computation-of-induced-power/511>\
**Category:** Mailing List Archive (read-only)\
**Tags:** list-archive\
**Created:** [November 23, 2012, 8:34am UTC](https://mne.discourse.group/t/edge-effects-in-computation-of-induced-power/511 "2012-11-23T08:34:03Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![system](https://global.discourse-cdn.com/free1/uploads/mne/original/1X/85cc6bd2b69cb698a166dc6d880fb550510d0144.jpeg) [@system](https://mne.discourse.group/u/system)\
**Post date:** [November 23, 2012, 8:34am UTC](https://mne.discourse.group/t/edge-effects-in-computation-of-induced-power/511/1 "2012-11-23T08:34:03Z")

</div>

Dear all,

I've been working recently with the Python toolbox trying to examine  
higher-frequency activity in an auditory paradigm. The PLV seems OK, but  
there are strange things happening at the edges of the induced power matrix  
which I think are obscuring whatever power is induced by the stimulus.  
When I process the sample dataset with the exact same script, I don't see  
such edge effects. Does anyone have any ideas about why this is  
happening?

A related general question: Is the evoked field subtracted from the  
individual epochs prior to computation?

Cheers,  
Andy

---

<div class="post-metadata">

**Author:** ![system](https://global.discourse-cdn.com/free1/uploads/mne/original/1X/85cc6bd2b69cb698a166dc6d880fb550510d0144.jpeg) [@system](https://mne.discourse.group/u/system)\
**Post date:** [November 24, 2012, 2:24pm UTC](https://mne.discourse.group/t/edge-effects-in-computation-of-induced-power/511/2 "2012-11-24T14:24:08Z")

</div>

hi Andy,

> I've been working recently with the Python toolbox trying to examine  
> higher-frequency activity in an auditory paradigm. The PLV seems OK, but  
> there are strange things happening at the edges of the induced power matrix  
> which I think are obscuring whatever power is induced by the stimulus. When  
> I process the sample dataset with the exact same script, I don't see such  
> edge effects. Does anyone have any ideas about why this is happening?

what you see is normal as no correction is done about edge artifact. The  
way I do it is by clipping the TFR maps at the beginning and at the end.  
Also baseline should not include the coefficients with artifact.

> A related general question: Is the evoked field subtracted from the  
> individual epochs prior to computation?

no. Separating evoked from induced by subtracting the mean is usually  
not enough.  
I agree that the term "induced" can therefore be misleading as  
currently described.

Feel free so send us some suggestions and code to improve this part of  
the mne-python  
code.

Best,  
Alex