TFR:boundaries, resolution

Christian Hesse c.hesse at FCDONDERS.RU.NL
Wed Mar 21 15:43:52 CET 2007

Hi Ulla,

> 1. Is there a way to get rid of boundary effects for low  
> frequencies. The boundary is moving but it is not disappearing.

You can't get rid of boundary effects as such. However, you could use  
a longer window in your time-frequency analysis and then only plot  
the part of the window without the edge effects.

> 2. The output is very grainy i.e. so called pixels are big and  
> sharp edged even with  as high tapsmofrq as is possible with  
> available memory. Is there a way to make the output prettier ?

The "pixels" are partly determined by the size of the time-frequency  
tiles (whose and their size is determined by the width of your time- 
window and frequency band at each point in your TFR) and the degree  
of overlap between the tiles. If you want to make things look  
"smoother" then you could try increasing the time resolution (spacing  
between windows) and the temporal smoothing (size of each window),  
and do the same for the frequency axis.

> 3. TopoplotTFR is not functioning. It only draws a blank figure.  
> MultiplotTFR and singleplotTFR function perfectly. I use .grad  
> generated layout for 306 channel Neuromag.

I have made a small change to the function PREPARE_LAYOUT which  
should fix the problem in TOPOPLOTTFR. The new version will be  
available with the daily update this evening at approximately 22:00  
CET (and is also attached).

The layout stuff has been undergoing some changes recently, and at  
present there does not really seem to be an appropriate way of  
passing a "pre-prepared, grad-generated" layout structure to the  
plotting functions. Currently, provided the gradiometer information  
is either in cfg.grad or in dat.grad, the plotting functions will  
automatically generate a layout structure using lay = prepare_layout 
(cfg, dat) every time they are called.

As a sort of compromise, you are (for the time being at least)  
allowed to put the pre-computed layout structure in cfg.layout, when  
you call TOPOPLOTTFR and it should work. In the future, I expect that  
an additional field for pre-computed layout structures might be added  
at some point.


Christian Hesse, PhD, MIEEE

F.C. Donders Centre for Cognitive Neuroimaging
P.O. Box 9101
NL-6500 HB Nijmegen
The Netherlands

Tel.: +31 (0)24 36 68293
Fax: +31 (0)24 36 10989

Email: c.hesse at

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