[FieldTrip] Question on ft_connectivity_psi

[Yale Cohen]

Hello

 

If I calculate the PSI value between 2 channels [channels A and B], the output of ft_connectivity_psi is a 3D matrix in which the first 2 indices are the PSI values of AA [always null], AB, BA, and BB [null]. The AB and BA values are the same magnitude but opposite sign indicating causal direction. The 3rd index is frequency.

 

If I now have more than 2 channels [A1, A2, etc, B1, B2,etc], the output of the matrix is NumChannelsA X NumChannelsB X Frequency. 

 

My question is how do I interpret the sign of the PSI value? Is it always correct to assume that the positive value indicates that Ax is driving Bx?

 

Thank you!

 

-- 

Yale E. Cohen, Ph.D. 

Professor
Associate Dean for Research Infrastructure and Strategy

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Department of Otorhinolaryngology:Head and Neck Surgery
University of Pennsylvania School of Medicine
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Office: G12A Stemmler 

 

E-mail: ycohen at pennmedicine.upenn.edu
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