Characterizing EMS-Induced Haptic Weight Perceptions: Effects of Posture, Augmentation Parameters, and User Variability

Electrical Muscle Stimulation (EMS) is a promising technology for rendering haptic weight perceptions in virtual reality, but its practical application is hindered by a limited understanding of the factors determining its realism and effectiveness. This study systematically examines the impact of elbow angle (45°, 90°, 135°), weight augmentation magnitude and base weight (using pairs from 0.15-5 kg), and individual user characteristics on perceived realism and required EMS intensity. In a within-subjects experiment with 35 participants, EMS was applied to the upper and lower arm during a weight-matching task where realism was rated on a 7-point Likert scale. Results revealed that ergonomics are critical: realism was significantly higher in the neutral 90° compared to the acute 45° angle, while the more open 135° angle was also rated as highly realistic. The required EMS intensity was also influenced by posture, with less current needed at 135°. Realism was primarily determined by the physical base weight-supporting a "sensory masking"hypothesis-while a 2.0 kg augmentation emerged as a secondary perceptual "sweet spot". Additionally, a learning effect improved realism after initial trials. Critically, correlations showed older age, higher BMI, and greater grip strength are associated with the outcomes, informing an "EMS efficiency"metric to better characterize user receptiveness. These findings provide guidelines for ergonomic, personalized haptic design, emphasizing adaptive systems to address inter-subject variability, with implications for immersive VR/AR applications.