\section{Conclusion}
\label{conclusion}

In this chapter, we investigated the visuo-haptic feedback of the hand when manipulating \VOs in immersive \OST-\AR using wearable vibrotactile haptic.
To do so, we provided vibrotactile feedback of the fingertip contacts with \VOs by moving away the haptic actuator that do not cover the inside of the hand: on the nails, the proximal phalanges, the wrist, and the nails of the opposite hand.
We selected these four different delocalized positions on the hand from the literature for direct hand interaction in \AR using wearable haptic devices.
In a user study, we compared twenty visuo-haptic feedback of the hand as the combination of two vibrotactile contact techniques, provided at five different delocalized positions on the user's hand, and with the two most representative visual hand augmentations established in the \chapref{visual_hand}, \ie the skeleton hand rendering and no hand rendering.

Results showed that delocalized vibrotactile haptic hand feedback improved the perceived effectiveness, realism, and usefulness when it is provided close to the contact point.
However, the farthest positioning on the contralateral hand gave the best performance even though it was disliked: the unfamiliarity of the positioning probably caused the participants to take more effort to consider the haptic stimuli and to focus more on the task.
The visual hand augmentation was perceived less necessary than the vibrotactile haptic feedback, but still provided a useful feedback on the hand tracking.
This study provide evidence that moving away the feedback from the inside of the hand is a simple but promising approach for wearable haptics in \AR.

If integration with the hand tracking system allows it, and if the task requires it, a haptic ring worn on the middle or proximal phalanx seems preferable.
However, a wrist-mounted haptic device will be able to provide richer feedback by embedding more diverse haptic actuators with larger bandwidths and maximum amplitudes, while being less obtrusive than a ring.
Finally, we think that the visual hand augmentation complements the haptic contact rendering well by providing continuous feedback on the hand tracking, and that it can be disabled during the grasping phase to avoid redundancy with the haptic feedback of the contact with the \VO.