Bimanual Ultrasound Mid-Air Haptics for Virtual Reality Manipulation.

The ability to manipulate and physically feel virtual objects without any real object being present and without equipping the user has been a long-standing goal in virtual reality (VR). Emerging ultrasound mid-air haptics (UMH) technology could potentially address this challenge, as it enables remote tactile stimulation of unequipped users. However, to date, UMH has received limited attention in the field of haptic exploration and manipulation in virtual environments. Existing work has primarily focused on interactions requiring a single hand and thus the delivery of unimanual haptic feedback. Despite being fundamental to a large part of haptic interactions with our environments, bimanual tasks have rarely been studied in the field of UMH interaction in VR. In this paper, we propose the use of non-coplanar mid-air haptic devices for providing simultaneous tactile feedback to both hands during bimanual VR manipulation. We discuss coupling schemes and haptic rendering algorithms for providing bimanual haptic feedback in bimanual interactions with virtual environments. We then present two human participant studies, assessing the benefits of bimanual ultrasound haptic feedback in a two-handed grasping and holding task and in a shape exploration task. Results suggest that the use of multiple non-coplanar UMH devices could be an interesting approach for enriching unencumbered haptic manipulation in virtual environments.