## 3 Feature Extraction
### Spike-Independent Features  
These features measure the LFP activity in MER segments and are mainly based on statistical, temporal, and spectral properties [24; 25; 26]. Each feature is computed for the 1 s MER segments. The list of features and their description is shown in Table 3. Detailed equations are shown in Appendix B.  
As an example, Figure 4 displays bispectrum (Bs) plots of STN-IN and STN-OUT MER segments. The bifrequency magnitude distinguishes between each class. Also, most of the  
\begin{table}
\begin{tabular}{l l} \hline \hline
**Features** & **Description** \\ \hline Spike Firing Rate (SFR) & Count of spikes per second. \\ \hline Inter Spike Interval (ISI) & Time intervals between consecutive spikes in the spike sequence [23]. \\ \hline Standard deviation of \(1S1\) (SISI) & Standard deviation of inter-spike intervals \(1S1\). \\ \hline Pause Ratio (PR) & Ratio of cumulative time of \(1S1\) greater than 50 ms to the cumulative time of ISI less than 50 ms. \\ \hline Pause Index (PI) & Ratio of the number of \(1S1\) greater than 50 ms to the number of \(1S1\) less than 50 ms. \\ \hline Bursting Rate (BR) & Number of bursts per second. \\ \hline Modified Burst Index (MBI) & Ratio of the number of \(1S1\) less than 10 ms to the number of \(1S1\) greater than 10 ms. \\ \hline \hline \end{tabular}
\end{table}
Table 2: Spike-dependent features obtained from MER segments.  
\begin{table}
\begin{tabular}{l l} \hline \hline
**Features** & **Description** \\ \hline \multirow{2}{*}{Bispectrum (Bs)} & The Fourier transform of the third-order cumulant spectrum [25]. \\ \cline{2-2} Zero crossing (Zc) & Number of zero crossings in the temporal domain [24]. \\ \hline Curve length (CI) & Sum of the difference of consecutive samples [27]. \\ \hline Integrator (In) & Sum of absolute value [24]. \\ \hline Root Mean Square (RMS) & Root mean square [24]. \\ \hline Kurtosis (Ku) & Peakiness coefficient variation [28]. \\ \hline Cumulative bispectrum (Cb) & Cumulative relationship between the higher-order moments [25]. \\ \hline Average Amplitude Change (AAc) & Average value of all amplitudes [24]. \\ \hline Short-Term Fourier Transform (STFT) & Spectrum energy from each MER segment [29]. \\ \hline Teager Energy (Te) & Energy rate induced from the second-order differential derivative of the amplitude and frequency variation [30]. \\ \hline Average First Amplitude difference (AFa) & Average of first amplitude difference [24]. \\ \hline Second Amplitude difference (SAd) & Average of second amplitude difference [24]. \\ \hline Standard deviation (SD) & Standard deviation [24]. \\ \hline Skewness (Sk) & Measure to quantify the presence of assymmetry in the shape of the distribution [31]. \\ \hline Slope Sign change (SSC) & Number of times that the slope of the MER curve changes its sign in the segment [24]. \\ \hline Variance (Va) & The signal’s averaged power [24]. \\ \hline \hline \end{tabular}
\end{table}
Table 3: List of spike-independent features based on the analysis of 1 s MER segments.  
magnitude of the bispectrum lies within \(-0.01\) to \(0.01\), and there is a random distribution of the magnitudes at various frequencies.