  This paper presents a wearable electrotactile feedback system to enable
precise and accurate contact rendering with virtual objects for mid-air
interactions. In particular, we propose the use of electrotactile feedback to
render the interpenetration distance between the user's finger and the virtual
content is touched. Our approach consists of modulating the perceived intensity
(frequency and pulse width modulation) of the electrotactile stimuli according
to the registered interpenetration distance. In a user study (N=21), we
assessed the performance of four different interpenetration feedback
approaches: electrotactile-only, visual-only, electrotactile and visual, and no
interpenetration feedback. First, the results showed that contact precision and
accuracy were significantly improved when using interpenetration feedback.
Second, and more interestingly, there were no significant differences between
visual and electrotactile feedback when the calibration was optimized and the
user was familiarized with electrotactile feedback. Taken together, these
results suggest that electrotactile feedback could be an efficient replacement
of visual feedback for accurate and precise contact rendering in virtual
reality avoiding the need of active visual focus and the rendering of
additional visual artefacts.
