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3-perception/xr-perception/1-introduction.tex

@@ -8,8 +8,8 @@ Most of the haptic augmentations of real surfaces using with wearable haptic dev
 Still, it is known that the visual rendering of an object 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}).
 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 \textbf{role of the visual feedback of the virtual hand and of the environment (real or virtual) on the perception of a real surface whose haptic roughness is augmented} with wearable vibrotactile haptics. %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 real surface being touched. % touched by the finger.% that can be directly touched with the bare finger.
+In this chapter, we investigate the \textbf{role of the visual feedback of the virtual hand and of the environment (real or virtual) on the perception of a real surface whose haptic roughness is augmented} with wearable vibrotactile haptics.
+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 real surface being touched.
 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 real surface was not visually augmented and stayed the same in all conditions.
 

3-perception/xr-perception/3-experiment.tex

@@ -1,9 +1,6 @@
 \section{User Study}
 \label{experiment}
 
-%The visuo-haptic rendering system, described in \secref[vhar_system]{method}, allows free exploration of virtual vibrotactile textures on real 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 real 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.
 

3-perception/xr-perception/4-results.tex

@@ -27,8 +27,8 @@ All pairwise differences were statistically significant.
 ]
 
 \begin{subfigs}{discrimination_accuracy}{Results of the vibrotactile texture roughness discrimination task. }[][
-  \item Estimated \PSE of each visual rendering, defined as the amplitude difference at which both reference and comparison textures are perceived to be equivalent. %, \ie the accuracy in discriminating vibrotactile roughness.
-  \item Estimated \JND of each visual rendering. %, defined as the minimum perceptual amplitude difference, \ie the sensitivity to vibrotactile roughness differences.
+  \item Estimated \PSE of each visual rendering, defined as the amplitude difference at which both reference and comparison textures are perceived to be equivalent.
+  \item Estimated \JND of each visual rendering.
   ]
   \subfig[0.35]{results/trial_pses}
   \subfig[0.35]{results/trial_jnds}
@@ -107,7 +107,6 @@ Participants were mixed between feeling the vibrations on the surface or on the
   {NASA-TLX questions asked to participants after each \factor{Visual Rendering} block of trials.}
   [
     Questions were bipolar 100-points scales (0~=~Very Low and 100~=~Very High, except for Performance where 0~=~Perfect and 100~=~Failure), with increments of 5.
-    %Participants were shown only the labels for all questions.
   ]
   \begin{tabularx}{\linewidth}{l X}
     \toprule

3-perception/xr-perception/5-discussion.tex

@@ -4,9 +4,6 @@
 The results showed a difference in vibrotactile roughness perception between the three visual rendering conditions.
 Given the estimated \PSEs, the textures were on average perceived as \enquote{rougher} in the \level{Real} rendering than in the \level{Virtual} (\percent{-2.8}) and \level{Mixed} (\percent{-6.0}) renderings (\figref{results/trial_pses}).
 A \PSE difference in the same range was found for perceived stiffness, with the \VR perceived as \enquote{stiffer} and the \AR as \enquote{softer} \cite{gaffary2017ar}.
-%
-%However, the difference between the \level{Virtual} and \level{Mixed} conditions was not significant.
-%
 Surprisingly, the \PSE of the \level{Real} rendering was shifted to the right (to be "rougher", \percent{7.9}) compared to the reference texture, whereas the \PSEs of the \level{Virtual} (\percent{5.1}) and \level{Mixed} (\percent{1.9}) renderings were perceived as \enquote{smoother} and closer to the reference texture (\figref{results/trial_predictions}).
 The sensitivity of participants to roughness differences also varied, with the \level{Real} rendering having the best \JND (\percent{26}), followed by the \level{Virtual} (\percent{30}) and \level{Mixed} (\percent{33}) renderings (\figref{results/trial_jnds}).
 These \JND values are in line with and at the upper end of the range of previous studies \cite{choi2013vibrotactile}, which may be due to the location of the actuator on the top of the finger middle phalanx, being less sensitive to vibration than the fingertip.
@@ -23,11 +20,9 @@ The \level{Mixed} rendering had the lowest \PSE and highest perceived latency, t
 
 Our wearable visuo-haptic texture augmentation system, described in \chapref{vhar_system}, aimed to provide a coherent visuo-haptic renderings registered with the \RE.
 Yet, it involves different sensory interaction loops between the user's movements and the visuo-haptic feedback (\figref[vhar_system]{diagram} and \figref[introduction]{interaction-loop}), which may not feel to be in synchronized with each other or with proprioception.
-%When a user runs their finger over a vibrotactile virtual texture, the haptic sensations and eventual display of the virtual hand lag behind the visual displacement and proprioceptive sensations of the real hand.
-%
 Thereby, we hypothesize that the differences in the perception of vibrotactile roughness are less due to the visual rendering of the hand or the environment and their associated differences in exploration behaviour, but rather to the difference in the \emph{perceived} latency between one's own hand (visual and proprioception) and the virtual hand (visual and haptic).
 The perceived delay was the most important in \AR, where the virtual hand visually lags significantly behind the real one, but less so in \VR, where only the proprioceptive sense can help detect the lag.
 This delay was not perceived when touching the virtual haptic textures without visual augmentation, because only the finger velocity was used to render them, and, despite the varied finger movements and velocities while exploring the textures, the participants did not perceive any latency in the vibrotactile rendering (\secref{results_questions}).
 \textcite{diluca2011effects} demonstrated similarly, in a \VST-\AR setup, how visual latency relative to proprioception increased the perception of stiffness of a virtual piston, while haptic latency decreased it (\secref[related_work]{ar_vr_haptic}).
 Another complementary explanation could be a pseudo-haptic effect (\secref[related_work]{visual_haptic_influence}) of the displacement of the virtual hand, as already observed with this vibrotactile texture rendering, but seen on a screen \cite{ujitoko2019modulating}.
-Such hypotheses could be tested by manipulating the latency and pose estimation accuracy of the virtual hand or the vibrotactile feedback. % to observe their effects on the roughness perception of the virtual textures.
+Such hypotheses could be tested by manipulating the latency and pose estimation accuracy of the virtual hand or the vibrotactile feedback.

3-perception/xr-perception/6-conclusion.tex

@@ -3,7 +3,6 @@
 
 In this chapter, we studied how the perception of wearable haptic augmented textures is affected by the visual feedback of the virtual hand and the environment, being either real, augmented or virtual.
 Using the wearable visuo-haptic augmentation system presented in \chapref{vhar_system}, we augmented the perceived roughness of real surfaces with virtual vibrotactile textures rendered on the finger.
-%we rendered virtual vibrotactile patterned textures on the voice-coil worn on the middle-phalanx of the finger to augment the roughness perception of the real surface being touched.
 With an \OST-\AR headset, that could be switched to a \VR only view, we considered three visual rendering conditions: (1) without visual augmentation, (2) with a realistic virtual hand rendering in \AR, and (3) with the same virtual hand in \VR.
 We then evaluated the perceived roughness augmentation in these three visual conditions with a psychophysical user study involving 20 participants and extensive questionnaires.
 
@@ -13,13 +12,10 @@ Similarly, the sensitivity to differences in roughness was better with the real
 Exploration behaviour was also slower in \VR than with real hand alone, although subjective evaluation of the texture was not affected.
 We hypothesized that this difference in perception was due to the \emph{perceived latency} between the finger movements and the different visual, haptic and proprioceptive feedbacks, which were the same in all visual renderings, but were more noticeable in \AR and \VR than without visual augmentation.
 
-%We can outline recommendations for future \AR/\VR studies or applications using wearable haptics.
 This study suggests that attention should be paid to the respective latencies of the visual and haptic sensory feedbacks inherent in such systems and, more importantly, to \emph{the perception of their possible asynchrony}.
 Latencies should be measured \cite{friston2014measuring}, minimized to an acceptable level for users and kept synchronized with each other \cite{diluca2019perceptual}.
 It seems also that the visual aspect of the hand or the environment on itself has little effect on the perception of haptic feedback, but the degree of visual virtuality can affect the asynchrony perception of the latencies, even though the latencies remain identical.
 When designing for wearable haptics or integrating it into \AR/\VR, it seems important to test its perception in real (\RE), augmented (\AE) and virtual (\VE) environments.
-%With a better understanding of how visual factors influence the perception of haptically augmented real objects, the many wearable haptic systems that already exist but have not yet been fully explored with \AR can be better applied and new visuo-haptic renderings adapted to \AR can be designed.
-%Finally, a visual hand representation in OST-\AR together with wearable haptics should be avoided until acceptable tracking latencies \are achieved, as was also observed for virtual object interaction with the bare hand \cite{normand2024visuohaptic}.
 
 In the next chapter we present a second user study where we investigate the perception of simultaneous and co-localised visual and haptic texture augmentation.
 We will use the same system presented in \chapref{vhar_system} and a visual rendering condition similar to the \level{Real} condition of this study, in \AR without the virtual hand overlay.