\chapter{Introduction}
\mainlabel{introduction}

This thesis presents research works on the perception and interaction with direct hands of everyday objects, visually and tactilely augmented with immersive and wearable augmented reality and haptic devices.

\sectionstartoc{Visual and Tactile Object Augmentations}

\subsectionstartoc{Everyday Interaction with Everyday Objects}

On a daily basis, we look and touch simultaneously the everyday objects that surround us, without even thinking about it.
%
Many these object properties can be perceived complementary by both vision and touch, such as their shapes, sizes or textures.
%
But vision often precedes touch, enabling us to expect the tactile sensations we will feel when touching the object, and even to predict properties that we cannot see, such as weight or temperature.
%
In this way, visual and tactile sensations are often linked and complementary, or even redundant or contradictory.
%
This is why we sometimes want to touch an object to check one of its properties that we have seen, such as its texture, and compare and confront our visual and tactile sensations.
%
We then instinctively construct a unified perception of the object we are exploring and manipulating from these two visual and tactile sensory modalities, as well as with the movement of our hand and fingers on the object.
%
Thus, one important aspect of touch is that is allows not only to perceive the environment, but also to interact with it.
%
Also called the haptic sense, it comprises two sub-modalities: kinesthetic (or proprioception), which are the forces felt by muscles and tendons, and cutaneous (or tactile sensations), which are the pressures, stretches, vibrations and temperatures felt by the skin.
%
This rich and complex diversity of haptic actions and sensations makes it particularly difficult to recreate artificially, for example in virtual or remote operation environments.

%Nous regardons et touchons simultanément les objets de la vie quotidienne qui nous entourent, sans même y penser.
%Beaucoup de propriétés de ces objets peuvent être perçues de façon complémentaire par la vision comme par le toucher, comme la forme, la taille ou la texture.
%Mais la vision précède souvent le toucher, et nous permet de prédire les sensations tactiles que nous allons ressentir en touchant l'objet, voire prédire des propriétés tactiles que nous ne pouvons pas voir, comme le poids ou la température.
%Ainsi, les sensations visuelles et tactiles sont souvent liées et complémentaires, voire redondantes ou contradictoires.
%C'est pourquoi nous voulons parfois toucher un objet pour vérifier une de ses propriété que nous avons vue, comme sa texture, et confronter nos sensations visuelles et tactiles.
%Nous utilisons alors ces deux modalités sensorielles, ainsi que le mouvement de notre main, pour construire une perception unifiée de l'objet que nous explorons et manipulons.
%Le sens du toucher permet ainsi à la fois de percevoir et d'interagir avec notre environnement.
%Également appelé sens haptique, il peut être décomposé en deux sous-modalités: les sensations kinésthétique (ou proprioception), qui sont les forces senties par les muscles et les tendons, et les sensations cutanées (ou tactiles), qui sont les pressions, étirements, vibrations et températures ressenties par la peau.
%Cette riche et complexe diversité de sensations rend particulièrement difficile de le recréer artificiellement, par exemple dans des environnements virtuels ou de téléopération.


\subsectionstartoc{Wearable Haptics and the Augmentation of Touch}

Present what is wearable haptics, how they can be used to augment the sense of touch~\autocite{pacchierotti2017wearable}. Detail then how they have been used with virtual reality, but how little they have been used with augmented reality.


\subsectionstartoc{Augmented Reality is Mostly Visual}

Explain what is augmented reality, and why it is important to use wearable haptics with it.


\sectionstartoc{Research Challenges}

Integrating wearable haptics and immersive augmented reality together to create a plausible and coherent visuo-haptic augmented environment that can be touched and manipulated directly with bare hands raises many perceptive and interaction challenges.
%
Each of these challenges also pose numerous design and technical issues specific to each of the two type of feedback, wearable haptics and augmented reality, as well as multimodal rendering and user experience issues in integrating these two sensorimotor feedbacks into the user's perception.
%
We identify two main research challenges which we address in this thesis:
%
\begin{enumerate*}[label=(\Roman*)]
    \item providing plausible and coherent visuo-haptic augmentations, and
    \item enabling effective interaction with the augmented environment.
\end{enumerate*}
%
These challenges are illustrated the visuo-haptic interaction loops in \figref{xxx}.

\subsectionstartoc{Provide Plausible and Coherent Visuo-Haptic Augmentations}



Le sens visuel nous permet de

\subsectionstartoc{Enable Effective Interaction with the Augmented Environment}


\sectionstartoc{Approach and Contributions}

The objective of this thesis is to understand how immersive visual and wearable haptic feedbacks compare and complement each other in the context of direct hand interaction with augmented and virtual objects.
%
Our approach is to
%
\begin{enumerate*}[label=(\arabic*)]
    \item design immersive and wearable multimodal visuo-haptic renderings that augment both the objects being interacted with and the hand interacting with them, and
    \item evaluate experimentally in user studies how these renderings affect the perception and manipulation of these objects using psychophysical, performance, and user experience methods.
\end{enumerate*}
%
We consider two main axes of research, each addressing one of the two research challenges identified above:
%
\begin{enumerate*}[label=(\Roman*)]
    \item augmenting the visuo-haptic texture perception of tangible surfaces, and
    \item improving virtual object manipulation with visuo-haptic augmentations of the hand.
\end{enumerate*}
%
Our contributions in these two axes are summarized in \figref{xxx}.

% TODO: Add figure with the two axes of research and the contributions

\subsectionstartoc{Augmenting the Visuo-Haptic Texture Perception of Tangible Surfaces}

\subsectionstartoc{Improving Virtual Object Manipulation with Visuo-Haptic Augmentations of the Hand}

% Touch allows to perceive the environment and interact with it, thus it motivates these two axes of research.

% it's a mix of augmented reality, virtual reality, vibrotactile feedback for visuo-tactile augmentation of the real world. Such multimodal rendering raise many questions on how to design, how renderings interact and complete each other, to give one perception

\sectionstartoc{Thesis Overview}

%Present the contributions and structure of the thesis.

This thesis is structured in four parts.
%
\partref{context} describes the context and background of our research, within which this first current \textit{Introduction} chapter presents the research challenges, and the objective, approach, and contributions of this thesis.
%
\chapref{related_work} then provides an overview of related work on the perception of and interaction with visual and haptic augmentations of objects.
%
First, it gives an overview of existing wearable haptic devices and renderings to provide diverse and rich tactile sensations to the user, with a focus on vibrotactile feedback.
%
Second, it presents the principles, current capabilities and limitations of augmented reality, and describes the 3D interaction techniques used in AR and VR environments to interact with virtual and augmented objects with, in particular, the visual rendering of the user's hand.
%
Finally, it shows how multimodal visuo-haptic feedback have been used in AR and VR to alter the perception of tangible objects and to improve the manipulation of virtual objects.
%
Then, we address each of our two research axes in a dedicated part.

\bigskip

\partref{perception} describes our contributions to the first axis of research, augmenting the visuo-haptic texture perception of tangible surfaces.
%
We evaluate how the visual rendering of the hand (real or virtual), the environment (AR or VR) and the textures (displayed or hidden) affect the roughness perception of virtual vibrotactile textures rendered on real surfaces and touched directly with the index finger.

\chapref{xr_perception} first details a system for rendering visuo-haptic virtual textures augmenting tangible surfaces using an immersive AR/VR headset and a wearable vibrotactile device.
%
The haptic textures are rendered as a real-time vibrotactile signal representing a grating texture, and is provided to the middle phalanx of the index finger touching the texture using a voice-coil actuator.
%
The tracking of the real hand and environment is done using marker-based technique, and the visual rendering of their virtual counterparts is done using the immersive AR headset Microsoft HoloLens~2.
%
It then presents a user study that evaluates how different the perception of virtual haptic textures is in AR \vs VR and when touched by a virtual hand \vs one's own hand.
%
We use psychophysical methods to measure the user roughness perception of the virtual textures, and extensive questionnaires to understand how this perception is affected by the visual rendering of the hand and the environment.

\chapref{ar_textures} presents the evaluation in a user study of the perception of visuo-haptic textures augmentations rendered on real tangible surfaces, using the system described in the previous chapter, and touched directly with one's own hand in AR.
%
The textures are paired visual and tactile models of real surfaces~\autocite{culbertson2014one}, and are rendered as visual texture overlays and as a vibrotactile feedback on the touched augmented surfaces, respectively.
%
We investigate the perception and user appreciation of the combination of nine representative visuo-haptic pairs of texture.
%
Our objective is to assess the perceived roughness of the visual and haptic textures and the coherence of their association.

\bigskip

\partref{manipulation} describes our contributions to the second axis of research, improving virtual object manipulation with visuo-haptic augmentations of the hand.
%
We evaluate how the visual and haptic rendering of the hand improve the direct manipulation of virtual objects with bare hands.

\chapref{visual_hand} explores how rendering a virtual visual hand showing how the

\chapref{visuo_haptic_hand} describes

\bigskip

\partref{part:conclusion} finally concludes this thesis and discuss short-term future works and long-term perspectives for each of our contributions and research axes.