[FieldTrip] calculating behavioural-power correlation -- follow-up questions

Thu Nov 12 18:07:25 CET 2015

Thanks Stephen, Arjen. 

I am using : MATLAB Version: 8.1.0.604 (R2013a) and fieldtrip-20151111.

I attached the 'testdata.mat' which has cfg and data_brain. I also
attached the error message I got from Matlab command window. 

Looking forward to your feedback!

Best,
Xiaoming

>>> Arjen Stolk <a.stolk8 at gmail.com> 11/12/2015 11:32 AM >>>
Hi Xiaoming,

Sounds like you're using an older version of the function. Did you try
updating fieldtrip?

Yours,
Arjen

2015-11-12 7:42 GMT-08:00 Stephen Whitmarsh <stephen.whitmarsh at ki.se>:

Dear Xiaoming,
It is working for me, using it in sourcestatistics. Have you checked
your design is really only one row? I can*t think of anything else*
Cheers,
S

From: fieldtrip-bounces at science.ru.nl
[mailto:fieldtrip-bounces at science.ru.nl] On Behalf Of Xiaoming Du
Sent: 12 November 2015 16:25
To: FieldTrip discussion list <fieldtrip at science.ru.nl>
Subject: Re: [FieldTrip] calculating behavioural-power correlation --
follow-up questions

Dear Arjen,

Thanks for the updates. 

I was trying to run the following code on Fieldtrip website
(http://www.fieldtriptoolbox.org/faq/how_can_i_test_for_correlations_between_neuronal_data_and_quantitative_stimulus_and_behavioural_variables)

% compute statistics with correlationT
cfg = [];
cfg.statistic = 'ft_statfun_correlationT';
cfg.method = 'montecarlo';
cfg.numrandomization = 1000;

n1 = 3; % n1 is the number of subjects
design(1,1:n1) = [0.6 0.9 0.1]; %here we insert our independent
variable (behavioral data) in the cfg.design matrix, in this case
reaction times of 3 subjects.

cfg.design = design;
cfg.ivar = 1; 

stat = ft_freqstatistics(cfg, data_brain{:});
 However, it gives me this error: 

Error using ft_statfun_correlationT (line 81)
uvar must be specified for dependent samples statistics

Error in ft_statistics_montecarlo (line 276)
[statobs, cfg] = statfun(cfg, dat, design);

Error in ft_freqstatistics (line 190)
[stat, cfg] = statmethod(cfg, dat, design);

Could you provide a sample data_brain, so I can organize my data into
same format? Thanks!

-Xiaoming

>>> Arjen Stolk <a.stolk8 at gmail.com> 11/7/2015 11:21 PM >>>

Dear participants in the discussion on behavioural-power correlation,
and interested folks, 

Following recent discussion on this mailing list (thanks to Xiaoming Du
and Martin Krebber), we have updated ft_statfun_correlationT, a function
that can be used for correlating neural and behavioral variables. 

Following the update, the correlation values calculated on genuine data
have not changed. However, the permutation procedure for calculating the
randomization distribution has. Namely, prior to the update the
permutation procedure would randomly permute across both the independent
(e.g., behavior) and dependent variables (e.g., neural data). This
procedure is prone to systematic bias across the data belonging to these
variables. And conceptually, as outlined in a new wiki page (see below),
the independent and dependent variables should be statistically
independent, meaning that any association between these variables should
be broken by randomly permuting the values of the independent variable.

http://www.fieldtriptoolbox.org/faq/how_can_i_test_for_correlations_between_neuronal_data_and_quantitative_stimulus_and_behavioural_variables?

Those that have been using ft_statfun_correlationT for calculating a
randomization distribution using the permutation procedure are advised
to update to the latest fieldtrip version and re-calculate those
distributions. We are sorry for any inconvenience this may cause. 

On a related note, the functionality of ft_statfun_correlationT (under
Pearson) is highly similar to that of ft_statfun_indepsamplesregrT. To
make the latter function, and others in the statfun suite, more
accessible, we would like to forward those interested to the above wiki
page where an overview is provided of the different approaches to
correlating neural and behavioral variables, with some example fieldtrip
code.

Yours, Arjen

on behalf of Eric Maris and Egbert Hartstra

2015-10-22 2:53 GMT-07:00 Maris, E.G.G. (Eric)
<e.maris at donders.ru.nl>:

Dear participants in the discussion on behavioural-power correlation,

My name is Eric Maris and have contributed most of the older statfuns
(but not ft_statfun_correlationT). Together with Arjen, I will try to
resolve some of the issues that have been discussed. Give us some time,
and we will return to you via the Discussion List.

best,
Eric

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