\section{Conclusion}
\label{conclusion}

In this chapter, we addressed the challenge of touching, grasping and manipulating \VOs directly with the hand in immersive \OST-\AR by providing and evaluating visual renderings as hand augmentation.
Superimposed on the user's hand, these visual renderings provide feedback from the virtual hand, which tracks the real hand, and simulates the interaction with \VOs as a proxy.
We first selected and compared the six most popular visual hand renderings used to interact with \VOs in \AR.
Then, in a user study with 24 participants and an immersive \OST-\AR headset, we evaluated the effect of these six visual hand renderings on the user performance and experience in two representative manipulation tasks.

Our results showed that a visual hand rendering overlaying the real hand improved the performance, perceived effectiveness and confidence of participants compared to no rendering.
A skeleton rendering, which provided a detailed view of the tracked joints and phalanges while not hiding the real hand, was the most performant and effective.
The contour and mesh renderings were found to mask the real hand, while the tips rendering was controversial.
The occlusion rendering had too much tracking latency to be effective.
This is consistent with similar manipulation studies in \VR and in non-immersive \VST-\AR setups.

This study suggests that a \ThreeD visual hand rendering is important in \AR when interacting with a virtual hand technique, particularly when it involves precise finger movements in relation to virtual content, \eg \ThreeD windows, buttons and sliders, or more complex tasks, such as stacking or assembly.
A minimal but detailed rendering of the hand that does not hide the real hand, such as the skeleton rendering we evaluated, seems to be the best compromise between the richness and effectiveness of the feedback.
%Still, users should be able to choose and adapt the visual hand rendering to their preferences and needs.