[Eeglablist] Study Plot channel ERSP GUI and script output

[Katharina Limbach]

Dear EEGLABers,

I have a question concerning the data structure underlying the plots made
with the GUI /Plot channel measures) and the output of the std_erspplot
function.

In short it seems to me, that the graphical output I get with the GUI and
the std_erspplot function is organized differently to the output cell
created by the std_ersp function, which is very confusing to me!

Here is what I am doing:
I have a study with a 2 x 2 design (novelty (Hits vs Correct Rejections
(CR)) and voice age (young vs. old) and 24 participants. I have 4 .set
files per participant and created the STUDY by using the condition input
for novelty (Hits and CR) and session for voice age (1 = young, 2 = old). I
set it up that way, so that I could later on built my designs by selecting
Condition as my first independent variable and Session as my second
independent variable.

I then precompute the channel measures to get the ERSP. When I afterwards
plot the results for one channel, I get a figure with 4 time-frequency
graphs.
The graphs are titled like this:
"CP4, 1, CR"    "CP4,1,Hits"
"CP4, 2, CR"    "CP4,2,Hits"
So the first row seems to show both conditions for the first session (i.e.
young voices) and the second row both conditions for the seond session
(i.e. old voices).

I then wanted to extract the data to do some some stats in a different
program.
I used the following code:
[STUDY erspdata ersptimes erspfreqs] = std_erspplot(STUDY, ALLEEG, ...
    'channels', {STUDY.changrp(55).name}); % 55 = channel CP4

(The graphs look the same as when created from the GUI.) The erspdata
output is a 2 x 2 cell array, and each element holds a 4-D matrix (22
(frequencies) 250 (timepoints)     1 (channel)   24 (participants)). So far
so good.
However, I then assumed that this cell would be organized like the
graphical output of the std_erspplot and the gui function.
So that
(1,1) 1,CR, (1,2) 1,Hits
(2,1) 2,CR  (2,2) 2,Hits.
However, that does not seem to be the case! It seems that the rows and
columns are switched and that the cell array is actually organized like
this:
(1,1) 1,CR, (1,2) 2,CR
(2,1) 1,Hits (2,2) 2,Hits.

One way I tested this was to average the erspdata across participants (per
cell) and then plot it using the Matlab imagesc function. The erspdata
output seems to be organized such that the rows represent the Condition and
the columns the Session (opposite to what it shown in the graphs).

Why is this happening? Is this a bug, or where I am doing something wrong?

I really appreciate your help,
Katharina
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