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. 2017 Jun 14;8:360. doi: 10.3389/fphys.2017.00360

Figure 4.

Figure 4

The standard univariate and the proposed bivariate stress parameters for 300 s sliding time windows, for the participants 1–3 in the experiments in Part 1. Upper: Stress parameters in 1D, that is, heart rate (HR), power in the low (LFp) and high frequency band (HFp), their ratio (LFp/HFp), the instantaneous amplitude in LF (LFiA), and the instantaneous amplitude in HF (HFiA). Lower: Proposed 2D stress parameters: LFiA-HFiA scatter diagrams for the instantaneous amplitude (iA) of LF and HF, where the background color designates the partitioning into stress categories, achieved through the SVM classifiers. While it is not possible to distinguish between the stress scenarios using 1D parameters (upper), the separation using 2D representations (upper) was perfect.