Ultrasonic Keyboard: A Mid-Air Virtual Qwerty with Ultrasonic Feedback for Virtual Reality

Free-hand mid-air Qwerty enables entering text in virtual reality without the use of controllers. However, it is much slower and more error prone than its physical counterpart, primarily due to the absence of haptic feedback and reduced spatial awareness. In this paper, we design three different ultrasonic haptic feedback for mid-air Qwerty: feedback only on keypress, on both touch and keypress, and gradual feedback that increases intensity as users push down a key. In a pilot study, the touch & press feedback performed significantly better both quantitatively and qualitatively. We then compare a mid-air Qwerty with and without touch & press feedback in a user study. Results revealed that haptic feedback improves entry speed by 16% and reduces error rate by 26%. Besides, most participants feel that it improves presence and spatial awareness in the virtual-world by maintaining a higher consistency with the real-world, and significantly reduces mental demand, effort, and frustration.