# Plant Electrical Signal Classification Based on Waveform Similarity
## 4 Results
### Classification Results of Our Proposed Method
#### 4.1.4 Features of AP waveforms  
Based on the APs characteristics and priori knowledge [1; 2; 3; 4; 5; 6; 8], 329 raw signals were divided into two classes: AP and non-AP. Moreover, non-AP include artifacts, subthreshold response, noise, transient interference, VPs, etc. As shown in Figure 8, there is a typical case of the observed raw signals induced by electrical stimulation, which consist of artifacts, subthreshold responses, and APs.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Append-Threshold** & **Update-Threshold** & **Accuracy** & **The Number of New Templates** \\ \hline
0.89 & 0.95 & 95.4\% & 38 \\
0.9 & 0.95 & 95.4\% & 27 \\
0.91 & 0.95 & 96.0\% & 24 \\
0.92 & 0.95 & 95.7\% & 21 \\
0.93 & 0.95 & 92.1\% & 19 \\
0.94 & 0.95 & 87.5\% & 13 \\
0.95 & 0.96 & 85.4\% & 13 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Different thresholds for template matching algorithm.  
Figure 7: AP recognition process (**a**) Raw signal; (**b**) Derivative signal.  
We extracted 19 features from 329 waveforms which include 96 non-AP waveforms and 233 standard AP waveforms. To test significant difference between every feature of AP and non-AP, we employed \(T\)-test (\(p\) < 0.05) (Table 4).  
\(T\)-test results show that there is a statistical difference in the average value of features between AP and non-AP including duration, left duration, right duration, left slope, amplitude, energy, power, LLE, Hjorth activity, Hjorth mobility, and Hjorth complexity. The rest features do not show a significant difference. Hence, we just selected the 11 features which show significant difference for classification.  
Only LLE shows real difference among non-linear features. LLE of AP and non-AP are all below zero which represents that the AP time series is not a chaotic process in this paper. The Hurst exponent of AP showed that AP signals are more stable and predictable.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Features** & **Non-AP (Mean \(\pm\) S.E.M.)** & **AP (Mean \(\pm\) S.E.M.)** \\ \hline Amplitude * (mV) & 14.33 \(\pm\) 9.90 & 20.57 \(\pm\) 12.55 \\ Durations * (s) & 8.01 \(\pm\) 4.35 & 9.75 \(\pm\) 5.05 \\ Rising duration * (s) & 2.36 \(\pm\) 1.31 & 3.00 \(\pm\) 1.62 \\ Decline duration * (s) & 5.75 \(\pm\) 3.61 & 6.85 \(\pm\) 4.22 \\ Rising slope * (mv/s) & 6.78 \(\pm\) 6.19 & 8.42 \(\pm\) 7.47 \\ Decline slope (mv/s) & 2.64 \(\pm\) 2.13 & 2.90 \(\pm\) 2.61 \\ Area & 4749.01 \(\pm\) 7728.3 & 6078.16 \(\pm\) 11,038.49 \\ Skewness & \(-\)0.57 \(\pm\) 0.71 & \(-\)0.50 \(\pm\) 0.65 \\ Kurtosis & 2.80 \(\pm\) 1.33 & 2.70 \(\pm\) 0.82 \\ Hjorth activity * & 27.27 \(\pm\) 34.44 & 48.82 \(\pm\) 54.37 \\ Hjorth mobility * & 0.16 \(\pm\) 0.10 & 0.14 \(\pm\) 0.07 \\ Hjorth complexity * & 1.89 \(\pm\) 0.71 & 2.17 \(\pm\) 0.91 \\ Energy * & 740,601.4 \(\pm\) 1,415,709 & 1,207,443 \(\pm\) 2,076,630 \\ Average power * & 8065.49 \(\pm\) 15,968.75 & 11,440.17 \(\pm\) 18,881.54 \\ Permutation entropy & 0.83 \(\pm\) 0.25 & 0.82 \(\pm\) 0.19 \\ Sample entropy & 0.05 \(\pm\) 0.05 & 0.05 \(\pm\) 0.05 \\ Correlation dimension & 0.75 \(\pm\) 0.24 & 0.74 \(\pm\) 0.22 \\ LLE * & \(-\)0.07 \(\pm\) 0.07 & \(-\)0.05 \(\pm\) 0.04 \\ Hurst & 0.99 \(\pm\) 0.07 & 0.99 \(\pm\) 0.04 \\ \hline \hline \end{tabular}  
* Statistically significant difference (\(p\) < 0.05) between Non-AP and AP. S.E.M. is standard error of the mean.  
\end{table}
Table 4: \(T\)-test for non-AP and AP features.  
Figure 8: Electrical signals induced by electrical stimulation. Green circle indicates artifact, blue rectangle indicates sub threshold response, and red rectangle indicates AP.