\section{Conclusion}
\label{conclusion}

Haptic perception and manipulation of objects with the hand involves exploratory movements or grasp types, respectively, with simultaneous sensory feedback from multiple cutaneous and kinaesthetic receptors embedded beneath the skin.
These receptors provide sensory cues about the physical properties of objects, such as roughness and hardness, which are then integrated to form a perception of the property being explored.
Perceptual constancy is possible in the absence of one cue by compensating with others.

Haptic systems aim to provide virtual interactions and sensations similar to those with real objects.
Only a few can be considered wearable due to their compactness and portability, but they are limited to cutaneous feedback.
If their haptic rendering is timely associated with the user's touch actions on a real object, the perceived haptic properties of the object, such as its roughness and hardness, can be modified.

\AR headsets integrate virtual content into the user's perception as if it were part of the \RE, with real-time tracking of the head and hands.
However, they lack direct hand interaction and manipulation of \VOs, which could be improved by visual rendering of the hand.
Tangibles are also used as proxies for manipulating \VOs, but can be inconsistent with the visual rendering, being haptically passives.
Wearable haptics on the hand is a promising solution for improving direct hand manipulation of \VOs and for coherent visuo-haptic augmentation of tangibles.

% the type of rendered object (real or virtual), the rendered haptic property (contact, hardness, texture, see \secref{tactile_rendering}), and .
%In this context of integrating \WHs with \AR to create a \vh-\AE (\chapref{introduction}), the definition of \textcite{pacchierotti2017wearable} can be extended to an additional criterion: The wearable haptic interface should not impair the interaction with the \RE, \ie the user should be able to touch and manipulate objects in the real world while wearing the haptic device.
% The haptic feedback is thus rendered de-localized from the point of contact of the finger on the rendered object.
