# [Eeglablist] Time Frequency Statistics

Arnaud Delorme arno at salk.edu
Fri Aug 27 17:36:26 PDT 2004

```David and Joe,

you may also use the function tftopo to find significant time-frequency
regions across subjects.

See this section of the EEGLAB manual
http://www.sccn.ucsd.edu/eeglab/scripttut/script_tutorial.html#script%20for%20performing%20time-frequency%20decompositions

The example above computes significance across channels but the same
strategy may be used to compute significance across subjects.
The function tftopo accepts time-frequency decompositions and bootstrap
arrays from several electrodes and subjects. It uses binomial statistic
on the bootstrap array of all subjects to mask non-significant
time-frequency regions (for instance, the function will plot significant
time-frequency regions in at least 7 out of 10 subjects).

Arno

Joseph Brooks wrote:

> David,
>
> The time-frequency analysis is done using a function called timef. One
> of the outputs of timef is a 2D matrix (time x frequency). This
> contains the data that is used to generate the time-frequency map that
> you see.
>
> In order to do a statistical analysis I do the following:
>
> (1) Write a script that will run the timef function on data from each
> subject and each condition.
> (2) The script saves the outputs of each run of timef into a matlab
> variable (I save things into structure variables....e.g. the structure
> may contain fields for each condition and then the subjects within that).
> (3) You can then save the output variables (a structure in my case) to
> disk.
> (4) Now, the time-frequency maps can be accessed and you can select
> any portion of the matrix that you choose.
> (5) run your statistical analysis of choice on some sub-matrix of
> interest of the time-frequency maps.
> (6) to take the mean across subjects, just stack the matrices from all
> the individual subjects into a 3D matrix and take the mean (using the
> mean function in matlab) over the subject dimension.
>
> Time and frequency are outputs of the timef function and will serve as
> axes for the time-frequency matrix.
>
> Type "help timef" at the matlab command line for full information
> about the use of timef.

--

*Arnaud Delorme, Ph.D.*
Computational Neurobiology Lab, Salk Institute
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>
*To think upon*:

If a free society cannot help the many who are poor, it cannot save
the few who are rich.

/John F Kennedy/

```