Table 1.
Adult pain facial expression descriptors, FACS action units and appearance [26], pain-related AUs and muscles [16,27].
Fig 1.
Study stimulation and measurements.
Table 2.
Data processing.
Table 3.
Time mark and period definitions used in the study.
Fig 2.
Test periods P0–P4 were defined by test time points stimulus start (t1), subject-reported pain threshold (t2), and pain tolerance (t3).
Fig 3.
Data distribution across test periods with respect to all tests and then only heat or electrical tests.
Bars represent the mean duration of each test period (P0–P4), and the confidence interval shows individual period standard deviations; All–all 120 tests, Heat–only heat stimulus, and Electrical–only electrical stimulus.
Fig 4.
Medians of standardized sEMG features (RMS and WL) across test periods P0–P4.
Muscle areas: cor = corrugator supercilii, orb = orbicularis oculi, lev = levator labii superioris, zyg = zygomaticus major, and ris = risorius; feature transformations: rms = root mean square, and wl = waveform length.
Table 4.
Pairwise comparison (Wilcoxon signed-rank, n = 31) across test periods P1–P4 using muscle sEMG feature medians of the individual subjects.
Table 5.
Inter-correlations (Spearman’s Rho) between the sEMG signals (input), and the period P1–P4.
Fig 5.
The average subject performance.
The average concordance performance (c-index) of the ordinal classification for each subject (ordered by average c-index) compared to the random prediction level (0.5). Red (dashed) line shows the average performance of the final model (0.64).