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2-perception/xr-perception/1-introduction.tex
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% Delivers the motivation for your paper. It explains why you did the work you did.
Most of the haptic augmentations of tangible surfaces using with wearable haptic devices, including roughness textures (\secref[related_work]{texture_rendering}), have been studied without a visual feedback, and none have considered the influence of the visual rendering on their perception or integrated them in \AR and \VR (\secref[related_work]{texture_rendering}).
\noindent Most of the haptic augmentations of tangible surfaces using with wearable haptic devices, including roughness textures (\secref[related_work]{texture_rendering}), have been studied without a visual feedback, and none have considered the influence of the visual rendering on their perception or integrated them in \AR and \VR (\secref[related_work]{texture_rendering}).
Still, it is known that the visual rendering of a tangible can influence the perception of its haptic properties (\secref[related_work]{visual_haptic_influence}), and that the perception of same haptic force-feedback or vibrotactile rendering can differ between \AR and \VR, probably due to difference in perceived simultaneity between visual and haptic stimuli (\secref[related_work]{ar_vr_haptic}).
Indeed, while in \AR, the user can see their own hand touching, the haptic device worn and the \RE, in \VR they are hidden by the \VE while.
Indeed, in \AR, the user can see their own hand touching, the haptic device worn and the \RE, while in \VR they are hidden by the \VE.
In this chapter, we investigate the role of the visual virtuality of the hand (real or virtual) and its environment (\AR or \VR) on the perception of a \textbf{tangible surface whose haptic roughness is augmented with a wearable vibrotactile} device worn on the finger.
In this chapter, we investigate the \textbf{role of the visual virtuality} of the hand (real or virtual) and its environment (\AR or \VR) on the perception of a \textbf{tangible surface whose haptic roughness is augmented} with a wearable voice-coil device worn on the finger.
To do so, we used the visuo-haptic system presented in \chapref{vhar_system} to render virtual vibrotactile patterned textures (\secref[related_work]{texture_rendering}) to augment the tangible surface being touched.% touched by the finger.% that can be directly touched with the bare finger.
We evaluated, in \textbf{user study with psychophysical methods and extensive questionnaire}, the perceived roughness augmentation in three visual rendering conditions: \textbf{(1) without visual augmentation}, in \textbf{(2) \OST-\AR with a realistic virtual hand} rendering, and in \textbf{(3) \VR with the same virtual hand}.
To control for the influence of the visual rendering, the tangible surface was not visually augmented.
To control for the influence of the visual rendering, the tangible surface was not visually augmented and stayed the same in all conditions.
\noindentskip The contributions of this chapter is: A psychophysical user study with 20 participants to evaluate the effect of visual hand rendering in \OST-\AR or \VR on the perception of haptic roughness texture augmentations, using wearable vibrotactile haptics.
\noindentskip The contributions of this chapter are:
\begin{itemize}
\item A psychophysical user study with 20 participants to evaluate the effect of visual hand rendering in \OST-\AR or \VR on the perception of haptic roughness texture augmentations, using wearable vibrotactile haptics.
\item A discussion and recommendations on the integration of wearable haptic augmentations in direct touch context with \AR and \VR.
\end{itemize}
\noindentskip In the remainder of this chapter, we first describe the experimental design and apparatus of the user study.
We then present the results obtained and discuss them before concluding.
We then present the results obtained, discuss them, and outline recommendations for future \AR/\VR works using wearable haptic augmentations.
%First, we present a system for rendering virtual vibrotactile textures in real time without constraints on hand movements and integrated with an immersive visual \AR/\VR headset to provide a coherent multimodal visuo-haptic augmentation of the \RE.
%An experimental setup is then presented to compare haptic roughness augmentation with an optical \AR headset (Microsoft HoloLens~2) that can be transformed into a \VR headset using a cardboard mask.

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2-perception/xr-perception/3-experiment.tex
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%The visuo-haptic rendering system, described in \secref[vhar_system]{method}, allows free exploration of virtual vibrotactile textures on tangible surfaces directly touched with the bare finger to simulate roughness augmentation, while the visual rendering of the hand and environment can be controlled to be in \AR or \VR.
%
The user study aimed to investigate the effect of visual hand rendering in \AR or \VR on the perception of roughness texture augmentation of a touched tangible surface.
%
In a \TIFC task (\secref[related_work]{sensations_perception}), participants compared the roughness of different tactile texture augmentations in three visual rendering conditions: without any visual augmentation (\level{Real}, \figref{renderings}), in \AR with a realistic virtual hand superimposed on the real hand (\level{Mixed}, \figref{renderings}), and in \VR with the same virtual hand as an avatar (\level{Virtual}, \figref{renderings}).
%
%The user study aimed to investigate the effect of visual hand rendering in \AR or \VR on the perception of roughness texture augmentation of a touched tangible surface.
In a \TIFC task (\secref[related_work]{sensations_perception}), participants compared the roughness of different tactile texture augmentations in three visual rendering conditions: without any visual augmentation (\level{Real}, \figref{experiment/real}), in \AR with a realistic virtual hand superimposed on the real hand (\level{Mixed}, \figref{experiment/mixed}), and in \VR with the same virtual hand as an avatar (\level{Virtual}, \figref{experiment/virtual}).
In order not to influence the perception, as vision is an important source of information and influence for the perception of texture \cite{bergmanntiest2007haptic,yanagisawa2015effects,vardar2019fingertip}, the touched surface was visually a uniform white; thus only the visual aspect of the hand and the surrounding environment is changed.
\begin{subfigs}{renderings}{
@@ -46,12 +44,12 @@ In the \level{Mixed} and \level{Real} conditions, the mask had two additional ho
\figref{renderings} shows the resulting views in the three considered \factor{Visual Rendering} conditions.
Participants sat comfortably in front of the box at a distance of \qty{30}{\cm}, wearing the HoloLens~2 with a cardboard mask attached, so that only the inside of the box was visible, as shown in \figref{experiment/apparatus}.
The vibrotactile voice-coil actuator (HapCoil-One, Actronika) was firmly attached to the middle phalanx of the right index finger of the participants using a Velcro strap.
The vibrotactile voice-coil actuator (HapCoil-One, Actronika) was firmly attached to the middle phalanx of the right index finger of the participants using a Velcro strap, similarly to previous studies \cite{asano2015vibrotactile,friesen2024perceived}.
The generation of the virtual texture is described in \secref[vhar_system]{texture_generation}.
They also wore headphones with a brown noise masking the sound of the voice-coil.
The user study was held in a quiet room with no windows, and took on average one hour to complete.
The user study was held in a quiet room with no windows.
\begin{subfigs}{setup}{Visuo-haptic texture rendering system setup. }[][
\begin{subfigs}{setup}{Visuo-haptic textures rendering setup. }[][
\item HoloLens~2 \OST-\AR headset, the two cardboard masks to switch the real or virtual environments with the same field of view, and the \ThreeD-printed piece for attaching the masks to the headset.
\item User exploring a virtual vibrotactile texture on a tangible sheet of paper.
]
@@ -82,6 +80,7 @@ All textures were rendered as described in \secref[vhar_system]{texture_generati
Preliminary studies allowed us to determine a range of amplitudes that could be felt by the participants and were not too uncomfortable.
The reference texture was chosen to be the one with the middle amplitude to compare it with lower and higher roughness levels and to determine key perceptual variables such as the \PSE and the \JND of each \factor{Visual Rendering} condition.
The chosen \TIFC task is a common psychophysical method used in haptics to determine \PSE and \JND by testing comparison stimuli against a fixed reference stimulus and by fitting a psychometric function to the participant's responses (\secref[related_work]{sensations_perception}).
The user study took on average one hour to complete.
\subsection{Experimental Design}
\label{experimental_design}