Comparing object lifting kinematics and the size-weight illusion between physical reality and virtual reality

This study compared the size-weight illusion (SWI) and object lifting kinematics between physical and virtual conditions, shedding light on the nuanced disparities in perception and action across different environmental mediums. We examined whether prior expectations about object weight based on size cues, which affect the experience of real-world object interactions, are different in virtual reality (VR). Employing a highly realistic virtual environment with precisely matched visual size and haptic cues, we tested the hypothesis that VR, which may be experienced as uncertain, unfamiliar, or unpredictable, would induce a smaller SWI due to a diminished effect of prior expectations. Participants (N = 25) reported the felt heaviness of lifted objects that varied in both volume and mass in physical reality and a VR environment. Reach and lift kinematics, and self-reported presence, were also recorded. Our findings showed no differences between how participants perceived the SWI between real and virtual environments, although there was a trend towards a smaller illusion in VR. Contrary to our predictions, participants who experienced more presence in VR did not experience a larger SWI-instead, the inverse relationship was observed. Notably, differences in reach velocities between physical and virtual conditions suggested a more controlled approach in VR. These findings highlight the intricate relationship between immersion and sensorimotor processes in virtual environments, emphasising the need for deeper exploration into the underlying mechanisms that shape human interactions with immersive technologies, particularly the prior expectations associated with virtual environments.