Automatic Coding of Facial Expressions of Pain: Are We There Yet?

Introduction. The experience of pain is regularly accompanied by facial expressions. The gold standard for analyzing these facial expressions is the Facial Action Coding System (FACS), which provides so-called action units (AUs) as parametrical indicators of facial muscular activity. Particular combinations of AUs have appeared to be pain-indicative. The manual coding of AUs is, however, too time- and labor-intensive in clinical practice. New developments in automatic facial expression analysis have promised to enable automatic detection of AUs, which might be used for pain detection. Objective. Our aim is to compare manual with automatic AU coding of facial expressions of pain. Methods. FaceReader7 was used for automatic AU detection. We compared the performance of FaceReader7 using videos of 40 participants (20 younger with a mean age of 25.7 years and 20 older with a mean age of 52.1 years) undergoing experimentally induced heat pain to manually coded AUs as gold standard labeling. Percentages of correctly and falsely classified AUs were calculated, and we computed as indicators of congruency, “sensitivity/recall,” “precision,” and “overall agreement (F1).” Results. The automatic coding of AUs only showed poor to moderate outcomes regarding sensitivity/recall, precision, and F1. The congruency was better for younger compared to older faces and was better for pain-indicative AUs compared to other AUs. Conclusion. At the moment, automatic analyses of genuine facial expressions of pain may qualify at best as semiautomatic systems, which require further validation by human observers before they can be used to validly assess facial expressions of pain.

Closing an Eye for the Reliability of Orbital Tightening in Pain Detection: A Model-Specific Simplification of the Mouse Grimace Scale

Despite its long establishment and its applicability in pain detection in mice, the Mouse Grimace Scale still seems to be underused in terms of acute pain detection during chronic experiments. However, a broadening of its applicability can identify possible refinement approaches such as cumulative severity and habituation to painful stimuli. Therefore, this study focuses on two main aspects: First, five composite MGS criteria were evaluated with two independent methods (the MoBPs algorithm and a penalized least squares regression) and ranked for their relative importance. The most important variable was used in a second analysis to specifically evaluate the context of pain after an i.p. injection (intervention) in two treatment groups (CCl4 and oil (control)) at fixed times throughout four weeks in 24 male C57BL/6N mice. One hour before and after each intervention, video recordings were taken and the MGS assessment was performed. In this study, the results indicate orbital tightening as the most important criterion. In this experimental setup, a highly significant difference after treatment between week 0 and 1 was found in the CCl4 group, resulting in a medium-sized effect (W = 62.5, p-value <0.0001, rCCl4= 0.64). The oil group showed no significant difference (week 0 vs 1, W = 291.5, p-value = 0.7875, rcontrol= 0.04). Therefore, the study showed that the pain caused by i.p. injections was only dependent on the applied substance and no significant cumulation or habituation occurred due to the intervention. Further, the results indicated that the MGS system can be simplified.

Race Deficits in Pain Detection: Medical Providers and Laypeople Fail to Accurately Perceive Pain Authenticity Among Black People

Across six studies ( N = 904), we suggest a novel mechanism for race disparities in pain treatment: Perceiver deficits in discriminating real from fake pain for Black (relative to White) individuals. Across Studies 1–4, White participants (Studies 1–4) and Black participants (Study 2) were better at discerning authentic from inauthentic pain expressions for White targets than for Black targets. This effect emerged for both subtle (Studies 1 and 2) and intense (Studies 3 and 4) pain stimuli. Studies 5 and 6 examined consequences for medical care decisions by examining pain treatment recommendations by laypeople (Study 5) and pain authenticity judgments by medical providers (Study 6). This work advances theory in pain perception, emotion judgment, and intergroup relations. It also has practical significance for identifying unexplored mechanisms causing racial disparities in medical care.

Can the Vocal Expression of Intellectually Disabled Individuals Be Used as a Pain Indicator? Initial Findings Supporting a Possible Novice Assessment Method

Pain is difficult to assess in non-verbal populations such as individuals with intellectual and developmental disability (IDD). Due to scarce research in this area, pain assessment for individuals with IDD is still lacking, leading to maltreatment. To improve medical care for individuals with IDD, immediate, reliable, easy to use pain detection methods should be developed. The goal of this preliminary study was to examine the sensitivity of acoustic features of vocal expressions in identifying pain for adults with IDD, assessing their feasibility as a pain detection indicator for those individuals. Such unique pain related vocal characteristics may be used to develop objective pain detection means. Adults with severe-profound IDD level (N = 9) were recorded in daily activities associated with pain (during diaper changes), or without pain (at rest). Spontaneous vocal expressions were acoustically analyzed to assess several voice characteristics. Analyzing the data revealed that pain related vocal expressions were characterized by significantly higher number of pulses and higher shimmer values relative to no-pain vocal expressions. Pain related productions were also characterized by longer duration, higher jitter and Cepstral Peak Prominence values, lower Harmonic-Noise Ratio, lower difference between the amplitude of the 1st and 2nd harmonic (corrected for vocal tract influence; H1H2c), and higher mean and standard deviation of voice fundamental frequency relative to no-pain related vocal productions, yet these findings were not statistically significant, possibly due to the small and heterogeneous sample. These initial results may prompt further research to explore the possibility to use pain related vocal output as an objective and easily identifiable indicator of pain in this population.