\chapter{Introduction}
\mainlabel{introduction}

\sectionstartoc{Wearable Haptics and Augmented Reality}

\subsectionstartoc{The Senses of Vision and Touch}

Touch is the only sense that allows not only to perceive the environment, but also to interact with it. Explain how both vision and touch are complementary and important for combined perception and interaction with the environment.


\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.
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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.
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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}

\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 hand interaction with augmented and virtual objects.
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Our approach is to
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\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{Overview}

%Present the contributions and structure of the thesis.

This thesis is structured in four parts.
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\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.
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\chapref{related_work} then provides an overview of related work on the perception of and interaction with visual and haptic augmentations of objects.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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We investigate the perception and user appreciation of the combination of nine representative visuo-haptic pairs of texture.
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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.