[Eeglablist] About the analysis result

[Arnaud Delorme]

>
> *1. what is the meaning for the blue and green curve in the figure? Is 
> it the similar meaning with channel time-frequency function? their 
> axis label seems different.*

The meaning of the curves is describe in the crossf and timef function 
help (this is true only in EEGLAB 4.2). It is different for timef and 
crossf. From crossf (from the help message):

   Assuming both 'plotamp' and 'plotphase' options are 'on' (=default), 
the upper panel
    presents the magnitude of either phase coherence or linear 
coherence, depending on
    the 'type' parameter (above). The lower panel presents the coherence 
phase difference
    (in degrees). Click on any plot to pop up a new window (using 
'axcopy()').
    -- The upper left marginal panel shows mean coherence during the 
baseline period
       (blue), and when significance is set, the significance threshold 
(dotted black-green).
    -- The horizontal panel under the coherence magnitude image 
indicates the maximum
       (green) and minimum (blue) coherence values across all 
frequencies. When significance
       is set (using option 'trials' for 'boottype'), an additional 
curve indicates the
       significance threshold (dotted black-green).

> ** *2. What is the meaning of BootStrap Signification value in it? How 
> will it affect the results?*

Computing a bootstrap distribution means that the (timef or crossf) 
function will apply the same formula it used to compute ERPS, ITC or 
coherence to the shuffled data (shuffled across time, across trials or 
both). For instance in timef, the data might be shuffled 200 times and 
the ERSP (Event-related Spectral Power) will be computed for each 
shuffling. You will end up with a bell-like distribution of ERSP values 
and if the non-shuffled ERSP "belongs" to this distribution (i.e. it is 
not in the 5% lowest or highest tails for instance), the ERSP (at this 
time point and frequency) is considered significant at 5%. These 
non-parametric statistics do not assume a probability distribution model 
for the measure (unlike a t-test for instance).

> *3. How can I save the results of channel cross-coherence function in 
> a file for later use?*
> **

If you are using the graphical interace. After calling the pop_timef for 
instance (menu "Plot > Time-frequency transforms > Channel 
time-frequency"). Type "h" on the command line to show the history

"figure; pop_timef( EEG, 1, 1, [-1000  2000], [3         0.5] ,'type', 
'phasecoher', 'topovec', 1, 'elocs', EEG.chanlocs, 'title','Channel FPz 
ERSP and ITC','padratio', 4, 'plotphase', 'off');"

copy and paste and add some outputs to the function:

figure; [ersp,itc,powbase,times,freqs,erspboot,itcboot] = pop_timef( 
EEG, 1, 1, [-1000  2000], [3         0.5] ,'type', 'phasecoher', 
'topovec', 1, 'elocs', EEG.chanlocs, 'title','Channel FPz ERSP and 
ITC','padratio', 4, 'plotphase', 'off');
(for details about the output see timef function help).

then save the outputs:

save -mat myfile.mat ersp itc powbase times freqs erspboot itcboot

these outputs may be combined for several subjects and used in the 
command line function tftopo() (no menu equivalent or graphical interface).

>  *4. (some out topic) Suppose, I have several subject EEG data stored 
> in different files. What post-process I need to do after finished the 
> channel cross-coherence function one by one for all subject?*

You may use tftopo above to combine all the coherences (note that tftopo 
is made to process timef outputs not crossf outputs, so the units on the 
figure might have to be slightly modified).

Best

Arno


-- 

*Arnaud Delorme, Ph.D.*
Computational Neurobiology Lab, Salk Institute
10010 North Torrey Pines Road
La Jolla, CA 92037 USA

*Tel* : /(+1)-858-458-1927 ext 15/
*Fax* : /(+1)-858-458-1847/
*Web page *: www.sccn.ucsd.edu/~arno <http://www.sccn.ucsd.edu/%7Earno>

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