  Mid-air interaction is one of the promising interaction modalities in virtual
reality (VR) due to its merits in naturalness and intuitiveness, but the
interaction suffers from the lack of haptic feedback as no force or
vibrotactile feedback can be provided in mid-air. As a breakthrough to
compensate for this insufficiency, the application of pseudo-haptic features
which create the visuo-haptic illusion without actual physical haptic stimulus
can be explored. Therefore, this study aimed to investigate the effect of four
pseudo-haptic features: proximity feedback, protrusion, hit effect, and
penetration blocking on user experience for free-hand mid-air button
interaction in VR. We conducted a user study on 21 young subjects to collect
user ratings on various aspects of user experience while users were freely
interacting with 16 buttons with different combinations of four features.
Results indicated that all investigated features significantly improved user
experience in terms of haptic illusion, embodiment, sense of reality,
spatiotemporal perception, satisfaction, and hedonic quality. In addition,
protrusion and hit effect were more beneficial in comparison with the other two
features. It is recommended to utilize the four proposed pseudo-haptic features
in 3D user interfaces (UIs) to make users feel more pleased and amused, but
caution is needed when using proximity feedback together with other features.
The findings of this study could be helpful for VR developers and UI designers
in providing better interactive buttons in the 3D interfaces.
