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Complete vhar_system conclusion

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\section{Summary}
In this thesis, entitled \enquote{\textbf{\ThesisTitle}}, we showed how wearable haptics, worn on the outside of the hand, can improve direct hand interaction in immersive \AR by augmenting the perception and manipulation of the virtual.
Wearable haptics can provide a rich tactile feedback on \VOs and augment the perception of real objects, both directly touched with the hand, while preserving the freedom of movement and interaction with the \RE.
In this thesis, entitled \enquote{\textbf{\ThesisTitle}}, we have shown how wearable haptics, worn on the outside of the hand, can improve direct hand interaction in immersive \AR by augmenting the perception and manipulation of the virtual.
Wearable haptics can provide a rich tactile feedback on \VOs and augment the perception of real objects, both directly touched by the hand, while preserving the freedom of movement and interaction with the \RE.
However, their integration with \AR is still in its infancy, and presents many design, technical and human challenges.
We structured our research on two axes: \textbf{(I) modifying the texture perception of tangible surfaces}, and \textbf{(II) improving the manipulation of \VOs}.
We have structured our research around two axes: \textbf{(I) modifying the texture perception of tangible surfaces}, and \textbf{(II) improving the manipulation of \VOs}.
\noindentskip In \partref{perception} we focused on modifying the perception of wearable virtual visuo-haptic textures that augments tangible surfaces.
\noindentskip In \partref{perception} we focused on modifying the perception of wearable and immersive virtual visuo-haptic textures that augment tangible surfaces.
Texture is a fundamental property of an object, perceived equally by sight and touch.
It is also one of the most known haptic augmentation, but it had not yet been integrated with \AR or \VR.
%However, haptic texture augmentation had not yet been integrated with \AR or \VR.
%We designed wearable visuo-haptic texture augmentations and evaluated how the degree of virtuality and the rendering of the visuals influenced the perception of the haptic textures.
We \textbf{(1)} proposed a \textbf{wearable visuo-haptic texture augmentation system}, \textbf{(2)} evaluated how the perception of haptic textures is \textbf{affected by the visual virtuality of the hand} and the environment (real, augmented, or virtual), and \textbf{(3)} investigated the \textbf{perception of co-localized visuo-haptic texture augmentations}.
It is also one of the most studied haptic augmentations, but it had not yet been integrated into \AR or \VR.
We \textbf{(1)} proposed a \textbf{wearable visuo-haptic texture augmentation system}, \textbf{(2)} evaluated how the perception of haptic texture augmentations is \textbf{affected by the visual virtuality of the hand} and the environment (real, augmented, or virtual), and \textbf{(3)} investigated the \textbf{perception of co-localized visuo-haptic texture augmentations}.
In \chapref{vhar_system},
In \chapref{vhar_system}, we presented a system for \textbf{augmenting any tangible surface} with virtual \textbf{visuo-haptic roughness textures} using an immersive \AR headset and a wearable vibrotactile device worn on the middle phalanx of the finger.
It allows a \textbf{free visual and touch exploration} of the textures, as if they were real, allowing the user to view them from different angles and touch them with the bare finger without constraints on hand movements.
The user studies in the next two chapters are based on this system.
In \chapref{xr_perception} we explored how the perception of wearable haptic augmented textures is affected by the visual virtuality of the hand and the environment, whether it is real, augmented or virtual.
We augmented the perceived roughness of the tangible surface with virtual vibrotactile patterned textures, and rendered the visual conditions by switching the \OST-\AR headset to a \VR-only view.
@@ -71,31 +71,31 @@ This would allow a complete portable and wearable visuo-haptic system to be used
The main limitation of this user study was the absence of a visual representation of the virtual patterned texture.
This is indeed a source of information as important as haptic sensations for the perception of both real textures \cite{baumgartner2013visual,bergmanntiest2007haptic,vardar2019fingertip} and virtual textures \cite{degraen2019enhancing,gunther2022smooth}, and their interaction in the overall perception is complex.
Specifically, it remains to be investigated how to visually represent the vibrotactile patterned textures in a way that is compelling, as the visuo-haptic coupling of such patterned textures is not trivial \cite{unger2011roughness}.% even with real textures \cite{klatzky2003feeling}.
In particular, it remains to be investigated how the vibrotactile patterned textures can be represented visually in a convincing way, as the visuo-haptic coupling of such patterned textures is not trivial \cite{unger2011roughness}.% even with real textures \cite{klatzky2003feeling}.
\paragraph{Broader Visuo-Haptic Conditions}
Our study was conducted with an \OST-\AR headset, but the results may be different with a \VST-\AR headset, where the \RE is seen through cameras and screens, and the perceived simultaneity between visual and haptic stimuli, real or virtual, is different.
We also focused on the perception of roughness augmentation using wearable vibrotactile haptics and a square wave signal to simulate a patterned texture: Our objective was not to accurately reproduce real textures, but to induce various roughness perception on the same tangible surface with a well controlled parameters.
Yet, more accurate models to simulate interaction with virtual textures should be transposed to wearable haptic augmentations, such as in \textcite{unger2011roughness}.
We also focused on the perception of roughness augmentation using wearable vibrotactile haptics and a square wave signal to simulate a patterned texture: Our objective was not to accurately reproduce real textures, but to induce different percevied roughness on the same tangible surface with a well controlled parameters.
However, more accurate models for simulating interaction with virtual textures should be applied to wearable haptic augmentations, such as in \textcite{unger2011roughness}.
Another limitation that may have affected the perception of the haptic texture augmentations is the lack of compensation for the frequency response of the actuator and amplifier \cite{asano2012vibrotactile,culbertson2014modeling,friesen2024perceived}.
The dynamic response of the finger should also be considered, and could vary among individuals.
The dynamic response of the finger should also be considered, and may vary between individuals.
\subsection*{Perception of Visual and Haptic Texture Augmentations in Augmented Reality}
\paragraph{Assess the Applicability of the Method}
As with the previous chapter, our objective was not to accurately reproduce real textures, but to alter the perception of a tangible surface being touched with simultaneous visual and haptic texture augmentations.
Yet, the results have also some limitations as they addressed a small set of visuo-haptic textures augmenting the perception of smooth and white tangible surfaces.
The visuo-haptic texture augmentation may be difficult on surfaces that already have strong visual or haptic patterns \cite{asano2012vibrotactile}, or on objects with complex shapes.
The role of visuo-haptic texture augmentations should also be evaluated in more complex tasks, such as object recognition and assembly, or in more concrete use cases, such as displaying and touching a museum object or a 3D print before manufacturing it.
As in the previous chapter, our aim was not to accurately reproduce real textures, but to alter the perception of a tangible surface being touched with simultaneous visual and haptic texture augmentations.
However, the results also have some limitations, as they addressed a small set of visuo-haptic textures that augmented the perception of smooth and white tangible surfaces.
Visuo-haptic texture augmentations may be difficult on surfaces that already have strong visual or haptic patterns \cite{asano2012vibrotactile}, or on objects with complex shapes.
The role of visuo-haptic texture augmentation should also be evaluated in more complex tasks, such as object recognition and assembly, or in more concrete use cases, such as displaying and touching a museum object or a 3D print before it is manufactured.
%Finally, the visual textures used were also simple color captures not meant to be used in an immersive \VE.
\paragraph{Adapt to the Specificities of Direct Touch}
The haptic textures used models from the vibrations of a hand-held probe sliding over real surfaces captured.
We generated the vibrotactile textures only from the finger speed \cite{culbertson2015should}, but the perceived roughness of real textures also depends on other factors, such as the force of contact, the angle, the posture or the surface of the contact \cite{schafer2017transfer}, but their respective importance in the perception is not yet fully understood \cite{richardson2022learning}.
The haptic textures used were captures and models of the vibrations of a hand-held probe sliding over real surfaces.
We generated the vibrotactile textures only from the finger speed \cite{culbertson2015should}, but the perceived roughness of real textures also depends on other factors, such as the contact force, the angle, the posture or the surface of the contact \cite{schafer2017transfer}, but their respective importance in the perception is not yet fully understood \cite{richardson2022learning}.
It would be interesting to determine the importance of these factors on the perceived realism of virtual vibrotactile textures.
The virtual texture models should also be adaptable to individual sensitivities \cite{malvezzi2021design,young2020compensating}.