HOW TO ANALYSE PHASE COHERENCE OF TWO RESPONSE WAVEFORMS IN ASCII FORMAT?

I have obtained the Vestibular evoked myogenic potential (VEMP) response waveforms by procuring an Amplitude modulated auditory stimuli to the subjects. I want to analyze whether there is a phase coherence between the stimuli waveform & response waveform and also, i want to analyze whether there is a phase coherence between the response waveforms obtained using each stimulus sweeps. i,e., I want to check if there is phase coherence within the response waveforms and also between the stimuli and response waveforms.

Please teach me on how to convert the VEMP waveforms into MATLAB- readable format and also please help me in creating a MATLAB code for analyzing the phase coherence.

Answer 1

[Suraj Kumar]

Hi @Aishwarya,

To analyse the phase coherence of two response waveforms in ASCII format, please refer to the steps mentioned below:

1. First we need to extract the raw data into MATLAB readable format. You can use various functions in MATLAB according to the original format. For example, in case or '.txt.' , '.csv' or '.xlsx' files, you can use the 'readtable' function in MATLAB.

2. Then we can use the Hilbert transform to extract the instantaneous phase and the Phase Locking Value(PLV).

To calculate Phase Locking Value (PLV) using the Hilbert transform, apply the Hilbert transform to each filtered signal to extract their instantaneous phases. For each pair of signals, compute the phase difference at each time point across all epochs.

Then, for each time point, calculate the PLV by taking the absolute value of the average of the complex exponentials of these phase differences across trials. The resulting PLV values, ranging between 0 and 1, indicate the degree of phase synchrony between the signals over time; higher values reflect stronger phase locking.

For more information on 'Hilbert Transformation, please refer to the following MATLAB documentation link:

https://www.mathworks.com/help/signal/ug/hilbert-transform.html

Happy Coding!