Assessment of Vigilance Level during Work: Fitting a Hidden Markov Model to Heart Rate Variability.

This study aimed to enhance the real-time performance and accuracy of vigilance assessment by developing a hidden Markov model (HMM). Electrocardiogram (ECG) signals were collected and processed to remove noise and baseline drift. A group of 20 volunteers participated in the study. Their heart rate variability (HRV) was measured to train parameters of the modified hidden Markov model for a vigilance assessment. The data were collected to train the model using the Baum-Welch algorithm and to obtain the state transition probability matrix A^ and the observation probability matrix B^. Finally, the data of three volunteers with different transition patterns of mental state were selected randomly and the Viterbi algorithm was used to find the optimal state, which was compared with the actual state. The constructed vigilance assessment model had a high accuracy rate, and the accuracy rate of data prediction for these three volunteers exceeded 80%. Our approach can be used in wearable products to improve their vigilance level assessment functionality or in other fields that have key positions with high concentration requirements and monotonous repetitive work.

Lighting environmental assessment in enclosed spaces based on emotional model.

Lighting assessment in special operating environments like enclosed spaces is of great research significance and value. In addition to investigating the visual ergonomics of workers, the emotional monitoring and guidance of workers in enclosed spaces is also a research focus. Based on the Circumplex emotion model theory, this paper designs an experiment to assess emotions in an enclosed space with 6 different lighting settings (2 correlated color temperature (CCT) × 3 illuminance levels). From the perspective of subjective assessment, participants used a rapid sensory analysis method (Check-all-that-apply, CATA) and a Subjective Coordinate Scale (SCS) method for rapid ambience perception checking and emotional self-reporting of lighting settings. From the perspective of objective evaluation, the participants' facial expressions were recorded during the experiment using a camera, and then the recorded facial expressions were automatically analyzed and predicted using FaceReader (FRE) software. The CATA and SCS showed similar results, with the 3100 K × 600 lx, 3100 K × 1000 lx and 6500 K × 600 lx lighting settings creating a relaxed, pleasant emotion in participants, the 6500 K × 1000 lx setting creating an excited, tense atmosphere, and the low illumination level settings of 3100 K × 250 lx and 6500 K × 250 lx made participants feel tired and frustrated. The results of the objective emotion analysis indicate that the FRE was able to effectively identify differences in participants' emotions in response to different lighting settings and was consistent with the results of participants' subjective emotion reports. This laboratory study validates that the three methods can effectively assess the enclosed space lighting settings, and provides a reference for further research on the enclosed space lighting settings and emotional monitoring of workers in the future.

Effects of aircraft tray table height and neck posture on passenger comfort: A study of the economy class cabin.

BACKGROUND: The tray table in economy class air travel may cause excessive neck flexion and discomfort in passengers. OBJECTIVE: The purpose of this study is to examine the influence of different tray table heights on the neck posture and discomfort perception of passengers. METHODS: A passenger experience survey was used to determine the passengers' view that the tray table was not high enough, and that most passengers were dissatisfied with the overall comfort evaluation of the tray table, especially passengers with obesity. Three head-neck angles and discomfort perceptions of six body parts in 58 participants were recorded by neck posture 3D scanning and perceived level of discomfort assessment, respectively. RESULTS: Tray tables at the original height (68 cm) caused unnatural neck posture and discomfort in participants. Raising the tray table can improve the neck posture of participants and reduce discomfort. However, raising the tray table too high will cause more shoulder discomfort in participants. Based on the results, 78 (±2) cm is suggested as the suitable thresholds range of tray tables for economy class air travel. CONCLUSION: The results and findings of this study could provide a theoretical base for the optimization of tray table design.