\section{Conclusion}
\label{conclusion}

In this chapter, we studied how the perception of wearable haptic augmented textures is affected by the visual virtuality of the hand and the environment.
Using the visuo-haptic augmentation system presented in \chapref{vhar_system}, we rendered virtual vibrotactile patterned textures

investigated virtual textures that modify the roughness perception of real, tangible surfaces, using a wearable vibrotactile device worn on the finger.

evaluated the perception of haptic textures on a tangible surface augmented with a wearable vibrotactile device worn on the finger.

different such wearable haptic augmented textures are perceived when touched with a virtual hand instead of one's own hand, and when the hand and its environment are visually rendered in AR or VR.

We investigated virtual textures that modify the roughness perception of real, tangible surfaces, using a wearable vibrotactile device worn on the finger.
%
%We studied how different such wearable haptic augmented textures are perceived when touched with a virtual hand instead of one's own hand, and when the hand and its environment are visually rendered in AR or VR.
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To this end, we first designed and implemented a visuo-haptic texture rendering system that allows free exploration of the augmented surface using a visual AR/VR headset.
%to render virtual vibrotactile textures on any tangible surface, allowing free exploration of the surface, and integrated them with an immersive visual OST-AR headset, that could be switched to a VR view.
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%This provided a coherent and synchronised multimodal visuo-haptic augmentation of the \RE, which could also be switched between an AR and a VR view.
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We then conducted a psychophysical user study with 20 participants to assess the roughness perception of these virtual texture augmentations directly touched with the finger (1) without visual augmentation, (2) with a realistic virtual hand rendering in AR, and (3) with the same virtual hand in VR.
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%The results showed that the visual rendering of the hand and environment had a significant effect on the perception of haptic textures and the exploration behaviour of the participants.
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The textures were on average perceived as \enquote{rougher} and with a higher sensitivity when touched with the real hand alone than with a virtual hand either in AR or VR.
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We hypothesised 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.
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With a better understanding of how visual factors influence the perception of haptically augmented tangible 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.

We can outline recommendations for future \AR/\VR studies or applications using wearable haptics.
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}.
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%This is in line with embodiment studies in \VR that compared realism, latency and control \cite{waltemate2016impact,fribourg2020avatar}.
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Latencies should be measured \cite{friston2014measuring}, minimised to an acceptable level for users and kept synchronised with each other \cite{diluca2019perceptual}.
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It seems 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 reality-virtuality can affect the asynchrony sensation of the latencies, even though they remain identical.
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%As we have shown, the visual representation of the hand or the environment can affect the experience of the unchanged latencies and thus the perception of haptic feedback.
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Therefore, when designing for wearable haptics or integrating it into \AR/\VR, it seems important to test its perception in real, augmented and virtual environments.
%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 \VO interaction with the bare hand \cite{normand2024visuohaptic}.

