[Eeglablist] time-frequency values

[Joseph Brooks]

Jeff,

I don't know how to do this using the graphical user interface for EEGlab, 
but I can do it at the command line. You can access the values of the ERSP 
image by using the timef function and assigning its outputs to matlab 
variables. The first variable that timef outputs is the ERSP matrix. So, 
for instance, if I have my data loaded into EEGlab, it is in a structure 
variable called EEG and I want to get a time-frequency plot for channel 26, 
then I could use something like the following function call at the command 
line:

[ersp26,itc,powerbaseline,times,freqs,Pboot,Rboot]=timef(EEG.data(26,:),307,[-200 
1000],256,0);

This will compute the ersp and assign it to the variable ersp26. Then you 
can access the values of the ERSP plot just by looking at the values of the 
matrix. If you want to find average power in certain frequency or time 
ranges, just use the mean function on the appropriate sub-matrix of ersp26.

Notice that other variables are assigned as well, itc is the inter-trial 
coherence image matrix, times = the times along the x-axis of the ERSP 
plot, freqs = the frequency bins along the y-axis of the ERSP plot, etc. 
Type help timef for a better description of all of the outputs and inputs 
of timef.

I have written several matlab programs to do grand average maps, and to 
look at average power within certain bands, etc. If you are pretty savvy 
with matlab it turns out to be pretty easy to write programs to 
automatically extract the information you want from a bunch of subjects at 
once.

I hope that this helps!

Joe


At 12:20 PM 5/20/2004 -0700, you wrote:
>Does anyone know if it's possible to extract the power (dB) values that 
>are produced by a channel time-frequency transform?  I'm trying to get the 
>actual value at each pixel that is mapped in the ERSP image, but I've had 
>no luck getting at the variables that represent this image.  Or is there a 
>better way to find the average power for a specified frequency band and epoch?
>Thanks in advance,
>Jeff
>
>_______________________________________________
>Eeglablist mailing list Eeglablist at sccn.ucsd.edu
>Eeglablist page: http://www.sccn.ucsd.edu/eeglab/eeglabmail.html
>To unsubscribe, send an empty email to eeglablist-unsub at sccn.ucsd.edu
>To switch to digest mode, send an empty email to 
>eeglablist-digest at sccn.ucsd.edu