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.

This work compares four mid-air target selection methods (Push, Tap, Dwell, Pinch) with two types of ultrasonic haptic feedback (Select, HoverSelect) in a Fitts’ law experiment. Results revealed that Tap is the fastest, the most accurate, and one of the least physically and cognitively demanding selection methods. Pinch is relatively fast but error prone and physically and cognitively demanding. Dwell is slowest by design, yet the most accurate and the least physically and cognitively demanding. Both haptic feedback methods improve selection performance by increasing users’ spatial awareness. Particularly, Push augmented with Hover & Select feedback is comparable to Tap. Besides, participants perceive the selection methods as faster, more accurate, and more physically and cognitively comfortable with the haptic feedback methods.