\section{Hand-Object Interactions in Visuo-Haptic Augmented Reality}
\label{visuo_haptic_ar}

% Answer the following four questions: “Who else has done work with relevance to this work of yours? What did they do? What did they find? And how is your work here different?”

\subsection{Altering the Perceptions}
\label{vhar_perception}

\subsubsection{Influence of Visual Rendering on Haptic Perception}
\label{vhar_influences}

When the same object property is sensed simultaneously by vision and touch, the two modalities are integrated into a single perception.
%
The phychophysical model of \textcite{ernst2002humans} established that the sense with the least variability dominates perception.


\subsubsection{Contact \& Hardness Augmentations}
\label{vhar_hardness}


\subsubsection{Texture Augmentations}
\label{vhar_texture}

Particularly for real textures, it is known that both touch and sight individually perceive textures equally well and similarly~\cite{bergmanntiest2007haptic,baumgartner2013visual,vardar2019fingertip}.
%
Thus, the overall perception can be modified by changing one of the modalities, as shown by \textcite{yanagisawa2015effects}, who altered the perception of roughness, stiffness and friction of some real tactile textures touched by the finger by superimposing different real visual textures using a half-mirror.

In 2010, they were research interest on building haptics (dynamic tactile feedback) for touch-based systems. [@Bau2010Teslatouch] created a touch-based surface rendering textures using electrovibration and friction feedback between the surface and the user's finger.
They extended this prototype to in [@Bau2012REVEL] to alter the texture of touched real objects using reverse electrovibration. They call this kind of haptic devices that can alter the touch perception of any object without any setup as *intrinsic haptic displays*. They said [@Azuma1997Survey] as envisioned this kind of AR experience.

Similarly but in VR, \textcite{degraen2019enhancing} combined visual textures with different passive haptic hair-like structure that were touched with the finger to induce a larger set of visuo-haptic materials perception.
\textcite{gunther2022smooth} studied in a complementary way how the visual rendering of a virtual object touching the arm with a tangible object influenced the perception of roughness.
Likewise, visual textures were combined in VR with various tangible objects to induce a larger set of visuo-haptic material perceptions, in both active touch~\cite{degraen2019enhancing} and passive touch~\cite{gunther2022smooth} contexts.
A common finding of these studies is that haptic sensations seem to dominate the perception of roughness, suggesting that a smaller set of haptic textures can support a larger set of visual textures.


\subsection{Improving the Interactions}
\label{vhar_interaction}

Conversely, virtual hand rendering is also known to influence how an object is grasped in VR~\cite{prachyabrued2014visual,blaga2020too} and AR, or even how real bumps and holes are perceived in VR~\cite{schwind2018touch}, but its effect on the perception of a haptic texture augmentation has not yet been investigated.

\subsubsection{Virtual Hands in Augmented Reality}
\label{vhar_hands}


\subsubsection{Wearable Haptics for Augmented Reality}
\label{vhar_haptics}
