[Eeglablist] crossf function output -- help?

[Danielle Farrar]

Hello everyone,

I'm trying to use the crossf function to get values for the coherence across
channels at different frequencies.  I'm having trouble with the
documentation of the function -- when I type help crossf into the matlab
command line, it says that the output is as follows:

Outputs:
        coh         = Matrix (nfreqs,timesout) of coherence magnitudes
        mcoh        = Vector of mean baseline coherence at each frequency
        timesout    = Vector of output latencies (window centers) (ms).
        freqsout    = Vector of frequency bin centers (Hz).
        cohboot     = Matrix (nfreqs,2) of [lower;upper] coher signif.
limits
                      if 'boottype' is 'trials',  (nfreqs,timesout, 2)
        cohangle    = (nfreqs,timesout) matrix of coherence angles (in
radians)
        cohangles   = (nfreqs,timesout,trials) matrix of single-trial
coherence
                       angles (in radians), saved and output only if
'savecoher',1

What I am trying to do is average some evoked potential data, and then
compare pair-wise, a series of the electrodes to determine their coherence,
which I will eventually write to a file.  I am new to this, so am having
trouble understanding how to interpret the output of the crossf function,
which I assume will give me what I am looking for.

So my questions is: the first output matrix that I get produces a 1.0 for
every cell in the matrix for the electrodes I've tried -- is it likely that
they are that in sync?  That should be giving me the matrix of coherence
magnitudes, correct? How is the coherence calculated?  I also print out the
mean baseline coherence, which also gives a matrix of 1s.

Here is a sample of the code I am trying to use (I am aware that the loops
will only be executed once, this is for debugging purposes):

*for **i=9:9,*

*    EEG = eeg_checkset( EEG );*

*    disp(i);*

*    disp(channels{i});*

*    erp = pop_erpimage(EEG,1, [i],[],wcst_rare,0,1,{},[],'' , 'yerplabel',
'\muV', 'erp', 'on', 'limits',[NaN NaN -25 25 NaN NaN NaN NaN] , 'cbar',
'on', 'vert',[170 300] );*

*    erp_avg = mean(erp,2);*

* *

*    for j=14:14,*

*       erp2 = pop_erpimage(EEG,1, [j],[],wcst_rare,0,1,{},[],'' ,
'yerplabel', '\muV', 'erp', 'on', 'limits',[NaN NaN -25 25 NaN NaN NaN NaN]
, 'cbar', 'on', 'vert',[170 300] );*

*       erp_avg2 = mean(erp2,2);*

*       [R, mbase, times, freqs]= crossf(erp_avg,erp_avg2,1150,[-150
999],1000,0,'type','coher');*

*       disp(*

*'Displaying coherence values');*

*       disp(R);*

*       disp(*

*'Displaying mean baseline coherence values');*

*       disp(mbase);*

*       disp(*

*'Displaying times');*

*       disp(times);*

*       disp(*

*'Displaying freqs');*

*       disp(freqs);*

*        disp('Size of times');*

*       disp(size(times));*

*       disp(*

*'Size of freqs');*

*       disp(size(freqs));*

*    end*

*end*
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