[Eeglablist] newtimef with large frequency windows

[Zachary Moran]

Hi Brad,

Thanks much for the response!  It will be helpful to know the exact window
size required for a successful decomposition.

As for why I'm using time-freq decompositions rather than a band pass
filter, it's because I'm interested in exploring the degree to which many
different frequency bins contribute to event-related waveforms rather than
just paring down the broadband signal.  As far as I'm aware, I don't think I
could do this through filtering, though if you know of a method I'd greatly
appreciate any help or references.  Also, I think wavelet transforms differ
from filters in terms of frequency resolution, roll-off/leakage especially
in the lower frequencies.

My big problem has been that the ERSP array that I get seems to be stuck
from 358.0 to 442.0 ms whereas I want to select elements of the array
corresponding to early, evoked potentials.  I think the decomposition will
enforce that this window be 84 ms long given the other dataset parameters,
but does anyone know if there is some way to recenter the window for a
different 84ms (e.g., 66 to 150)?

Thank you!!

Zach

On Sun, Aug 10, 2008 at 3:31 PM, Bradley Voytek <bradley.voytek at gmail.com>wrote:

> Zach:
>
> Your decomposition parameters require a 558 ms windows on either side
> of your epoch, so if you want a 200 ms baseline you'll have to have a
> minimun time of your epoch be (200 + 558) = 758 ms. Your ending time
> of 1000ms should be sufficient for the timing of the ERP components of
> interest.
>
> That said, with such a large pass band, why not just band pass your
> raw signal between 3 and 60 Hz? Why bother with a time-frequency
> decomposition?
>
> ::brad
>
>
> On Sat, Aug 9, 2008 at 2:57 PM, Zachary Moran <zdmoran at gmail.com> wrote:
> > Hi all,
> >
> >
> > At the moment I'm working on a project in which I'm trying to get ERSP
> > estimates around some early evoked potentials (e.g., between 20 and 100
> > ms).  Though I'd like to implement a frequency window of 3 to 60 Hz, when
> I
> > attempt to do so, EEGLAB forces the output to fall within a window of
> 358.0
> > to 442.0 ms.  Unfortunately, the only way I'm able to get to earlier
> > time-points is to increase my minimum frequency to around 12 Hz thus
> > allowing for an overall larger time window.  However, I have seen the
> sort
> > of analysis that I'm looking for done (I think in EEGLAB, since it used
> ERSP
> > and ITC specifically) by Brockhaus-Dumke et al. (2008)  "Sensory gating
> > revisited: Relation between brain oscillations and auditory evoked
> > potentials in schizophrenia."  I've included an example of my script
> below:
> >
> > <<figure; pop_newtimef( EEG, 1, 1, [-200  1000], [3         0.5] ,'type',
> > 'phasecoher', 'topovec', 1, 'elocs', EEG.chanlocs, 'chaninfo',
> EEG.chaninfo,
> > 'title','ERSP and ITC','padratio', 1, 'plotphase','off','freqs',[3
> 60]);>>
> >
> > My dataset is sampled at 1000 Hz and has 1201 frames per epoch.  Does
> anyone
> > have any experience with this who knows how I might get around this
> problem
> > or any way of recentering the output window around desired ERP components
> > (e.g., from 75 to 125)?  Any help or information would be very greatly
> > appreciated.
> >
> >
> > Thank you very much,
> >
> >
> > Zach
> >
> >
> > Zachary Moran
> > Graduate Student
> > University of California-Los Angeles
> >
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